JP2006304367A - Modulation circuit and transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simply and readily integrate circuit with other circuit blocks, and to efficiently operate by applying to an IC card that inputs/outputs various data in a contactless manner and to a reader/writer that communicates with the IC card, e.g., in a modulation circuit and a transmitter. <P>SOLUTION: On the output side of a power amplifier circuit, the result of power amplification is attenuated, corresponding to the input data to generate an amplitude modulated signal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a modulation circuit and a transmission device, and can be applied to, for example, an IC card that inputs and outputs various data without contact and a reader / writer that performs data communication with the IC card. The present invention, on the output side of the power amplifier circuit, attenuates the power amplification result according to the input data and generates an amplitude modulation signal, so that it can be easily and easily integrated with other circuit blocks. Further, it is possible to operate efficiently.

  Conventionally, an IC card system using an IC card is applied to a ticket gate system for transportation, a room entrance / exit management system, and the like. Such an IC card system is composed of an IC card carried by the user and a reader / writer that transmits / receives various data to / from these IC cards. It has been proposed to send and receive.

  That is, in this type of IC card system, the reader / writer modulates a carrier wave having a predetermined frequency with a desired data string to generate a transmission signal, and sends the transmission signal to the IC card.

  The IC card receives this transmission signal via the antenna, and demodulates data transmitted from the reader / writer based on this transmission signal. Further, the IC card modulates data such as personal information held in the IC card with a predetermined carrier according to the received data and sends it to the reader / writer.

  The reader / writer receives data sent from the IC card, and opens / closes the door of the ticket gate and permits entry / exit of the room based on the received data.

  In such an IC card system, for example, these data are transmitted and received between the IC card and the reader / writer by ASK (Amplitude Shift Keying) modulation. Conventionally, as such ASK modulation means, variable gain amplification is used. A modulation circuit using a circuit and a multiplication circuit is used, and as a means for demodulating an ASK modulation signal, an envelope detection circuit using a diode or the like and a demodulation circuit using a synchronous detection circuit are used.

  FIG. 33 is a block diagram showing a modulation circuit using this variable gain amplifier circuit. In this modulation circuit 1, the gain of the variable gain amplifier circuit 2 is switched according to the logic level of the data string D to be transmitted, and this variable The gain amplifier circuit 2 amplifies the carrier signal SC. As a result, the modulation circuit 1 modulates the amplitude of the carrier signal SC output from the variable gain amplification circuit 2 in accordance with the logic level of the data string D, and generates an ASK modulation signal SM.

  FIG. 34 is a block diagram showing a modulation circuit having a balanced modulation circuit configuration using a multiplication circuit. In this modulation circuit 3, the multiplication circuit 4 multiplies the carrier signal SC and the data string D, whereby data The ASK modulation signal SM is generated by changing the amplitude of the carrier signal SC according to the logic level of the column D.

  On the other hand, FIG. 35 is a block diagram showing a demodulation circuit having a configuration of a envelope detection circuit using a diode. In the demodulation circuit 6, the ASK modulation signal SM is rectified using the diode D. Further, the rectified ASK modulation signal SM is input to a smoothing circuit having a predetermined time constant by a resistor R and a capacitor C, and thereby, the envelope detection output of the ASK modulation signal SM is output as a demodulated signal SD.

  FIG. 36 is a block diagram showing a demodulating circuit having a synchronous detection circuit configuration. In this demodulating circuit 8, for example, a carrier signal component SCC from an ASK modulated signal SM by a phase synchronization system circuit 9 having a filter circuit configuration and a PLL circuit configuration. Is extracted, and the carrier signal component SCC and the ASK modulation signal SM are multiplied by the multiplication circuit 10. In the demodulation circuit 8, a baseband component is extracted from the multiplication result of the multiplication circuit 10 by a low-pass filter (LPF) 12 and output as a demodulated signal SD.

  By the way, in an IC card system, it is required that these modulation circuit and demodulation circuit can be integrated with other circuit blocks easily and easily and operate more efficiently.

  However, the conventional modulation circuit and demodulation circuit as described above have a problem that they do not sufficiently satisfy the requirements for these IC card systems.

  That is, the modulation circuit using the variable gain amplifier circuit has a drawback that the power efficiency is poor because the voltage range in which the variable gain amplifier circuit can be effectively used is limited. Further, a modulation circuit using a multiplication circuit has a disadvantage that it has a complicated circuit configuration and is difficult to easily and easily be integrated.

  Incidentally, even in the power amplification circuit of an ASK modulation signal that is required to be integrated with such a modulation circuit, it is necessary to preserve and amplify the change in amplitude in the ASK modulation signal. The power amplifier circuit must operate in a region, and the power amplifier circuit has a disadvantage that power efficiency is deteriorated. In addition, the power amplifier circuit has a drawback that an active element that satisfies required allowable current, allowable loss, and the like must be used instead of a general-purpose component that can be easily obtained in order to transmit sufficient power. .

  On the other hand, the demodulation circuit having the configuration of the envelope detection circuit using the diode has a drawback that leakage current is generated in the diode due to the integration of the integrated circuit, thereby significantly reducing the detection efficiency of the ASK modulation signal. That is, as shown in FIG. 37, when the envelope detection circuit using a diode is integrated, a parasitic transistor is always generated in the diode D because both polarities need to be set to a floating potential. As a result, a leak current is generated as shown in FIG.

On the other hand, the demodulation circuit having the synchronous detection circuit configuration has a drawback that the configuration of the phase synchronization system circuit 9 itself is complicated.
JP-A-10-203066

  The present invention has been made in consideration of the above points. A modulation circuit that can be easily and easily integrated with other circuit blocks and can operate more efficiently, and transmission using this modulation circuit. The device is to be proposed.

  In order to solve the above problems, the invention of claim 1 is applied to a modulation circuit, and has a variable attenuator that attenuates the power amplification result of the power amplification circuit in accordance with an input signal at the output terminal of the power amplification circuit. Then, the output signal of the power amplifier circuit is modulated to an amplitude modulation signal corresponding to the input signal.

  The invention according to claim 7 is applied to a transmission apparatus having a modulation circuit based on amplitude modulation, and the modulation circuit attenuates the power amplification result of the power amplification circuit in accordance with an input signal at an output terminal of the power amplification circuit. And a variable attenuator for modulating the output signal of the power amplifier circuit into an amplitude modulation signal corresponding to the input signal.

  Further, the invention of claim 8 is applied to a transmission device that modulates an input signal to transmit an amplitude-modulated signal, and generates a first amplitude-modulated signal according to the input signal; A second modulation circuit for generating a second amplitude modulation signal in which a phase of a carrier wave is inverted with respect to the first amplitude modulation signal in accordance with the input signal; and the first and second amplitude modulations Arithmetic means for adding or subtracting signals to generate the amplitude modulation signal, and the first modulation circuit outputs the power according to the input signal at an output terminal of a power amplification circuit for amplifying a carrier wave; A variable attenuator for attenuating the power amplification result of the amplifier circuit; and modulating the output signal of the power amplifier circuit into the first amplitude modulation signal corresponding to the input signal; and At the output terminal of the power amplifier circuit that inverts and amplifies the carrier wave And a variable attenuator for attenuating the power amplification result of the power amplifier circuit according to the input signal, and modulating the output signal of the power amplifier circuit to the second amplitude modulation signal according to the input signal Like that.

  According to the configuration of claim 1, claim 7, or claim 8, the power amplifier circuit can amplify the carrier wave signal without generating the amplitude component and generate the amplitude modulation signal. As a result, the power efficiency can be improved as compared with the prior art, and it can be configured by easily available general-purpose components, and can be easily and easily integrated with other circuit blocks.

  According to the present invention, an integrated circuit can be easily and easily integrated with other circuit blocks, and can operate more efficiently.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

(1) Configuration of Embodiment 1 FIG. 2 is a block diagram showing an IC card system according to Embodiment 1 of the present invention. This IC card system 21 is applied to a ticket gate system for transportation, for example, and exchanges data between the IC card 22 and the reader / writer 23. In addition, this Example 1 is not contained in this application, and is a reference example of this application to the last.

  Here, the IC card 22 is formed in a card shape by laminating a substrate on which an integrated circuit is mounted and a protective sheet. The IC card 22 has a loop antenna 24 formed by a wiring pattern on the substrate. Further, the modulation / demodulation circuit 25 and the signal processing circuit 26 are formed by an integrated circuit mounted on the substrate.

  Here, the loop antenna 24 is coupled to the loop antenna 28 of the reader / writer 23 to receive the transmission signal transmitted from the loop antenna 28 and radiate the response signal generated by the modem circuit 25.

  The modem circuit 25 generates power, a clock, and the like necessary for the operation of the IC card 22 from the transmission signal received by the loop antenna 24. Further, the modem circuit 25 operates with the power and the clock, demodulates the data string (hereinafter referred to as a transmission data string) D (R → C) sent from the reader / writer 23, and outputs it to the signal processing circuit 26. A transmission signal is generated by the transmission data string D (R → C) and a response signal based on an ASK modulation signal is generated from a data string (hereinafter referred to as a response data string) D (C → R) input from the signal processing circuit 26. Then, the response signal is radiated by driving the loop antenna 24 by the response signal.

  The signal processing circuit 26 operates with the power and clock generated by the modulation / demodulation circuit 25, analyzes the transmission data string D (R → C), and, if necessary, the response data string D (held in the built-in nonvolatile memory). C → R) is output to the modem circuit 25.

  In the reader / writer 23, the modulation / demodulation circuit 29 generates a transmission signal based on the ASK modulation signal from the transmission data string D (R → C) input from the SPU (signal processing unit) 30, and drives the loop antenna 28 by this transmission signal. To do. The modulation / demodulation circuit 29 performs signal processing on the response signal received by the loop antenna 28, demodulates the response data sequence D (C → R) sent from the IC card 22, and the response data sequence D (C → R) is output to the SPU 30.

  The SPU 30 is composed of an arithmetic processing unit that executes a relatively simple processing procedure. The SPU 30 sends a transmission data string D (R → C) to be transmitted to the IC card 22 to the modulation / demodulation circuit 29 and is input from the modulation / demodulation circuit 29. The response data string D (C → R) is processed. In this process, the SPU 30 displays the process progress and the process result on the display unit 31 as necessary. Further, the operation is switched by a command from the input unit 32, and data such as a processing procedure is input / output to / from the external device 33 as necessary.

  FIG. 3 is a block diagram showing a partial configuration of the modulation / demodulation circuit 29 of the reader / writer 23. The modem circuit 29 includes a transmission side block 45 and a reception side block 46.

  Here, the transmission side block 45 modulates the transmission data string D (R → C) output from the SPU 30 according to the control signal RFoff output from the SPU 30 and transmits it from the loop antenna 28. Therefore, the transmission side block 45 generates a carrier signal SC having a frequency of 13.56 [MHz] by a built-in oscillation circuit, and also decodes the transmission data string D (R → C) and converts it into a transmission data string by Manchester code. To do.

  In the ASK modulation circuit 47, the transmission block 45 ASK modulates the carrier signal SC with the transmission data string TX (D (R → C)) encoded in this way, and generates an ASK modulation signal SM. Further, the power amplification circuit 48 amplifies the ASK modulation signal SM and drives the loop antenna 28.

  The receiving side block 46 processes the response signal SM obtained via the loop antenna 28 and demodulates the response data string D (C → R). That is, the receiving block 46 detects the response signal SM obtained via the loop antenna 28 in the ASK detection circuit 49, and the detection signal whose signal level changes according to the logic level of the response data string D (C → R). SD is generated. The reception side block 46 band-limits the detection signal SD by the subsequent low-pass filter (LPF) 50, and then amplifies the detection signal SD with a predetermined gain by the amplifier circuit 51 and binarizes it. Further, the reproduction data obtained by the binarization is decoded, thereby reproducing and outputting the response data string D (C → R).

  FIG. 1 is a block diagram illustrating the configuration principle of an ASK modulation circuit 47 and a power amplification circuit 48 (hereinafter referred to as a transmission circuit). The transmission circuit 55 includes two systems of processing circuits 55A and 55B each having a power amplification circuit.

  Here, the first processing circuit 55A receives the carrier signal SC through the buffer amplifier circuit 56, and outputs the output signal of the buffer amplifier circuit 56 having the same phase as the carrier signal SC to the second selection input terminal of the selection circuit 57. input. Here, the selection circuit 57 inputs a signal having an opposite phase to the carrier signal SC to the first selection input terminal from the second processing circuit 55B, and grounds the remaining third selection input terminal. The selection circuit 57 switches contacts under the control of the control circuit 58, and the subsequent power amplification circuit 59 amplifies and outputs the output signal of the selection circuit 57.

  Accordingly, the first processing circuit 55A is configured to switch the contact of the selection circuit 57 between the first and third contacts and to gate a signal having an opposite phase to the carrier signal SC. Similarly, the contact of the selection circuit 57 is switched between the second and third contacts so that a signal having the same phase as the carrier signal SC can be gated.

  On the other hand, the second processing circuit 55B has the same amplification factor as that of the buffer amplifier circuit 56 and inputs the carrier wave signal SC to the buffer amplifier circuit 60 having an inverting amplifier circuit configuration. Accordingly, the second processing circuit 55B generates a signal having an opposite phase to the carrier signal SC, and inputs the signal having the opposite phase to the first selection input terminal of the selection circuit 61. Here, the selection circuit 61 inputs a signal having the same phase as the carrier wave signal SC from the first processing circuit 55B to the second selection input terminal, and grounds the remaining third selection input terminal. The selection circuit 61 switches contacts under the control of the control circuit 58, and the subsequent power amplification circuit 62 amplifies and outputs the output signal of the selection circuit 61.

  As a result, the second processing circuit 55B is also configured to switch the contact of the selection circuit 61 between the first and third contacts and to gate a signal having an opposite phase to the carrier signal SC. Similarly, the contact of the selection circuit 61 is switched between the second and third contacts so that a signal having the same phase as the carrier signal SC can be gated.

  The transmission circuit 55 connects the outputs of the processing circuits 55A and 55B by wiring and outputs them to the antenna. Thus, as shown in FIG. 4, in the transmission circuit 55, when the power outputs of the power amplification circuits 59 and 62 are P1 and P2, respectively, the contact of the selection circuit 57 or 61 is held on the ground side (see FIG. 4). When the contact of the selection circuit 61 or 57 is switched, the transmission output by the powers P1 and P2 can be obtained with the same phase and the opposite phase, respectively.

  When the contact of the selection circuit 57 or 61 is set to the same phase side or the opposite phase side and the remaining contact of the selection circuit 61 or 57 is switched and the input signal of the power amplification circuit 62 or 59 is gated, the power amplification circuit 59 And 62, the transmission power output from the antenna can be switched. As a result, the transmission circuit 55 can obtain an ASK modulated signal SM that has been subjected to power amplification at the output terminals of the power amplification circuits 59 and 62.

  The control circuit 58 generates an ASK modulation signal SM from the transmission data string TX by switching the contacts of the selection circuits 57 and 61 according to the transmission data string TX. That is, as shown in FIG. 5, the control circuit 58 is set to always select the output on the buffer amplifier circuit 56 side on the selection circuit 61 side (FIG. 5C), and the logical level of the transmission data string TX is set. In response to this, the contacts of the selection circuit 57 are switched to gate the input signal (FIGS. 5A and 5B), thereby generating an ASK modulation signal SM that is amplified in power (FIG. 5D). Although FIG. 5 shows the case where the contact of the selection circuit 57 is switched between the output on the buffer amplifier circuit 56 side and the ground, the ASK modulation signal can be generated in the same manner even when switching other than these combinations. Even if the operations of the selection circuits 57 and 61 are switched, and the contacts of the selection circuits 57 and 61 are simultaneously switched, the ASK modulation signal can be similarly generated.

  FIG. 6 is a block diagram showing a specific ASK modulation circuit 47 and power amplification circuit 48 according to this embodiment. This transmission circuit 65 has two systems of transmission circuits 65A and 65B that drive both ends of the loop antenna 28, respectively, and the above-described two systems of processing circuits 55A and 55B are equalized to each of the transmission circuits 65A and 65B. Composed.

  That is, the transmission circuit 65A inputs the carrier signal SC with the same phase via the buffer amplifier circuit 66, and inputs this carrier signal SC to the power amplifier circuits 67 and 68. Here, as shown in FIG. 7, the power amplifier circuits 67 and 68 include a P-channel MOS field effect transistor T1, an N-channel MOS field effect transistor T2, and a control logic 70.

  Among these, the P-channel MOS field effect transistor T1 and the N-channel MOS field effect transistor T2 are connected in series and arranged between the power source and the ground, and are connected according to the gate voltage set by the control logic 70. A switching circuit for switching the potential of the output terminal consisting of dots is configured.

  As shown in the truth table in FIG. 8, when the control terminal input OEI is set to H level, the control logic 70 sets the gate terminals of the field effect transistors T1 and T2 to H level and L level, respectively. Here, the control logic 70 sets the gate end logic level by changing the voltage at the gate end more than the drain-source voltage of the field effect transistors T1 and T2. As a result, the control logic 70 stops the power amplification process, and at this time, the output terminal is held at high impedance.

  Further, when the control terminal input OEI is set to the L level, the control logic 70 switches the gate terminals of the field effect transistors T1 and T2 according to the logic level of the input terminal in, and thereby, according to the logic level of the input terminal in. The power amplification process is stopped and controlled so that the output signal of the power amplification circuit can be gated according to the logic level of the input terminal in.

  The power amplifying circuit 67 receives the control signal RFoff from the control terminal input OEI of the control logic 70, so that the control signal RFoff can be switched as necessary to stop the power amplifying process. Can be reduced.

  The power amplifier circuit 68 inputs the logical sum output of the control signal RFoff obtained through the OR gate 75 and the transmission data string TX to the control terminal input OEI of the control logic 70, so that the operation can be stopped together with the power amplifier circuit 67. Has been made. When the power amplification circuit 67 is executing power amplification processing, the power amplification processing is stopped according to the logic level of the transmission data string TX, and the power amplification output in phase with the power amplification output of the power amplification circuit 67 Has been made to gate. Further, when the power amplification process is stopped according to the logic level of the transmission data string TX, the output terminals of the field effect transistors T1 and T2 are held at high impedance so as not to become a load on the power amplification circuit 67. Has been made.

  As a result, the power amplifier circuits 67 and 68 each constitute a tri-state buffer circuit.

  The transmission circuit 65A supplies the power amplification output of the power amplification circuit 68 to one end of the loop antenna 28, and supplies the power amplification output of the power amplification circuit 67 to one end of the loop antenna 28 via the resistor 69. Thus, the power amplification outputs of these power amplification circuits 67 and 68 are added via a resistor 69 to generate an ASK modulation signal SMA. The transmission circuit 65A is configured such that a monitoring terminal TMA is disposed at the output end on the power amplification circuit 67 side.

  On the other hand, in the second transmission circuit 65B, a buffer amplification circuit 71 having an inverting amplification circuit configuration is arranged in place of the buffer amplification circuit 66 in the first transmission circuit 65A, and power amplification is performed at the other end of the loop antenna 28. The configuration is the same as that of the first transmission circuit 65A except that an output is supplied. As a result, the second transmission circuit 65B generates an ASK modulation signal SMB having an inverted phase in conjunction with the first transmission circuit 65A, and drives the loop antenna 28 with the ASK modulation signal SMB.

(2) Operation of Embodiment 1 In the above configuration, the IC card system 21 (FIGS. 2 and 3) is configured such that the transmission data string D (R → C) transmitted from the reader / writer 23 to the IC card 22 is the modulation / demodulation circuit 29. ASK modulated and transmitted from the loop antenna 28.

  As a result, when the IC card 22 approaches the reader / writer 23, a transmission signal SM based on the ASK modulation signal is induced in the loop antenna 24 of the IC card 22. A part of the induced transmission signal SM is converted into the power of the IC card 22, and the modulation / demodulation circuit 25 and the signal processing circuit 26 of the IC card 22 are driven by this power.

  Further, the transmission signal SM obtained from the loop antenna 24 is demodulated by the modulation / demodulation circuit 25, and the transmission data string D (R → C) is analyzed by the signal processing circuit 26. A response data string D (C → R) to be sent to the reader / writer 23 is generated. In the IC card 22, this response data string D (C → R) is ASK modulated by the modulation / demodulation circuit 25, and the ASK modulation signal SM obtained as a result is sent out from the loop antenna 24 as a response signal.

  As a result, the response data string D (C → R) is transmitted from the IC card 22 to the reader / writer 23. The response signal SM transmitted in this way is received by the reader / writer 23 by the loop antenna 28 coupled to the loop antenna 24, and the response data string D (C → R) is demodulated by the modem circuit 29.

  The transmission data string D (R → C) transmitted and received in this way (FIGS. 3 to 5) is ASK modulated by the ASK modulation circuit 47, further amplified by the power amplification circuit 48, and transmitted from the loop antenna 28. The

  In this embodiment, when the ASK modulation circuit 47 performs ASK modulation and the power amplification circuit 48 amplifies the power (FIG. 1), the power amplification output of the power amplification circuit 59 that amplifies the carrier signal SC by a predetermined phase On the other hand, the power amplification output of the power amplification circuit 62 that similarly amplifies the carrier wave signal SC with a predetermined phase is gated and added according to the logic level of the transmission data string D (R → C), thereby adding power. An amplified ASK modulation signal is generated.

  As a result, each of the power amplifier circuits 59 and 62 can be designed mainly considering power efficiency without much consideration of linearity, and the power efficiency can be improved as compared with the conventional one. Further, it can be configured by easily available general-purpose parts.

  On the other hand, in ASK modulation, an ASK modulation signal can be generated by simply gating the output signal in the amplification circuits 59 and 62, so that ASK modulation can be performed with a simple configuration suitable for integration, and power efficiency can be improved. It becomes possible to improve.

  More specifically, in the power amplifying circuits 67 and 68 having a tri-state buffer circuit configuration that amplifies the carrier signal SC with the same phase (FIG. 6), in one power amplifying circuit 67, the transmission data string D (R → C ) Always amplifies the power of the carrier signal SC. On the other hand, in the other power amplifier circuit 68, the carrier signal SC is power-amplified in accordance with the logic level of the transmission data string D (R → C), thereby the logic level of the transmission data string D (R → C). Accordingly, the power amplification result is gated, and the power amplification results of the power amplification circuits 67 and 68 are added through the resistor 69 to drive the loop antenna 28. As a result, at both ends of the loop antenna 28, the amplitude of the carrier signal SC obtained by power amplification changes in accordance with the logic level of the transmission data string D (R → C), and the loop antenna 28 is activated by the ASK modulation signals SMA and SMB. Will be driven.

  As a result, the power amplifier circuits 67 and 68 can be designed mainly considering the power efficiency without much consideration of linearity, and the power efficiency can be improved as compared with the related art. Further, it can be configured by easily available general-purpose parts.

  In the ASK modulation, the ASK modulation signal can be generated simply by intermittently stopping the power amplification process in the amplifier circuit 68 and gating the output signal, and the ASK with a simple configuration suitable for the integrated circuit. Modulation is possible and power efficiency can be improved.

  The power amplifying circuits 67 and 68 that amplify the power in this way are formed by connecting a P-channel field effect transistor T1 and an N-channel field effect transistor T2 in series (FIG. 7), and these field effect transistors. The power amplification processing is stopped and controlled by changing the gate voltages of T1 and T2 to be higher than the voltages between the drain and the source and holding the gate voltages at the H level and the L level, respectively.

  As a result, when transmitting the transmission data string D (R → C), the power amplification circuit 67 that always amplifies the power of the carrier signal SC is intermittently transmitted according to the logic level of the transmission data string D (R → C). In the power amplifying circuit 68 that amplifies the power, the output terminal is held in a high impedance state during the period in which the power amplifying process is stopped. It keeps the output from being consumed. This also improves power efficiency. Further, since the source current itself of the field effect transistors T1 and T2 hardly flows, this also improves the power efficiency.

(3) Effects of Embodiment 1 According to the above configuration, the power for amplifying the carrier signal SC with the predetermined phase is similarly applied to the power amplification output of the power amplification circuit 59 for amplifying the carrier signal SC with the predetermined phase. The power amplification output of the amplifying circuit 59 is designed by mainly considering power efficiency without much consideration of linearity by gating and adding according to the logic level of the transmission data string D (R → C). An ASK modulation signal can be generated using a power amplifier circuit. As a result, the power efficiency can be improved as compared with the prior art, and it can be constituted by easily available general-purpose parts. In addition, a modulation circuit and a power amplification circuit that can be easily and easily integrated with other circuit blocks and can operate more efficiently can be obtained.

  In addition, by configuring the power amplifier circuit using an amplifier circuit with a tri-state buffer circuit configuration that switches the output terminal to high impedance when operation is stopped, power efficiency can be improved by simple control, and so on. A power amplifier circuit that can be easily and easily integrated with the circuit block and that can operate efficiently can be obtained.

  FIG. 9 shown in comparison with FIG. 1 is a block diagram showing the configuration principle of an ASK modulation circuit applied to the second embodiment of the present invention. In this ASK modulation circuit 79, the power amplification results of the power amplification circuits 59 and 62 are supplied to the two antennas 28A and 28B, respectively, and the two power amplification results are added in the electromagnetic field transmitted from the antennas 28A and 28B. To do. In addition, this Example 2 is not contained in this application, and is a reference example of this application to the last.

  As shown in FIG. 9, the same effect as in the first embodiment can be obtained even if the two power amplification results are added in the electromagnetic field.

  FIG. 10 is a block diagram showing the configuration principle of the ASK modulation circuit applied to the third embodiment of the present invention. In this embodiment, the ASK modulation circuit 80 is applied in place of the ASK modulation circuit 47 and the power amplification circuit 48 (FIG. 3) of the reader / writer 23.

  That is, in the ASK modulation circuit 80, the carrier wave signal SC is amplified by the power amplification circuit 81 and then output through the variable attenuator 82. Here, the variable attenuator 82 attenuates and outputs the carrier signal in accordance with the transmission data string TX (D (R → C)), and thereby in accordance with the transmission data string TX (D (R → C)). An ASK modulation signal SM having a changed amplitude is output.

  Incidentally, as this type of variable attenuator 82, as shown in FIG. 11, the transmission line is terminated, as shown in FIG. 12, the transmission line is inserted in series, and as shown in FIG. Thus, the thing of the format which concerns on these combinations is applied.

  Specifically, the configuration shown in FIG. 14 is applied to the ASK modulation circuit according to this embodiment. That is, in the ASK modulation circuit 90, the carrier wave signal SC is input to the buffer amplifier circuit 91, and the output signal of the buffer amplifier circuit 91 is amplified by the power amplifier circuit 92. The power amplifier circuit 92 supplies the power amplification result to one end of the loop antenna 28 via the resistor 93, and one end of the loop antenna 28 is grounded via the resistor 94 and the field effect transistor T3. As a result, the ASK modulation circuit 90 constitutes a variable attenuator whose attenuation is switched by controlling the on / off of the field effect transistor T3, and the power amplifying result output from the power amplifying circuit 92 by the variable attenuator is converted into the ASK. Modulate.

  In the ASK modulation circuit 90, the carrier wave signal SC is input to the buffer amplifier circuit 95 having an inverting amplifier circuit configuration, and the output signal of the buffer amplifier circuit 95 is amplified by the power amplifier circuit 96. The power amplifier circuit 96 supplies the power amplification result to the other end of the loop antenna 28 via the resistor 97, and the other end of the loop antenna 28 is grounded via the resistor 98 and the field effect transistor T4. As a result, the ASK modulation circuit 90 constitutes a variable attenuator whose attenuation is switched by controlling the on / off of the field effect transistor T4, and the power amplifying result output from the power amplifying circuit 96 by this variable attenuator is converted into the ASK. Modulate.

  According to the configuration according to the third embodiment, on the output side of the power amplifier circuit, the power amplification result is attenuated according to the transmission data string TX to generate the ASK modulation signal SM. An ASK modulated signal can be generated by amplifying the carrier signal without preserving the components. As a result, the power amplifier circuit can be operated in a saturation region. For example, the power amplifier circuit can be configured by a logic IC having high versatility such as a CMOS standard logic IC or a TTL circuit. Therefore, the power efficiency can be improved as compared with the conventional one, and it can be constituted by a readily available general-purpose component, and can be easily and easily integrated with other circuit blocks, and further efficient. Can work well.

  FIG. 15 shown in comparison with FIG. 10 is a block diagram showing the configuration principle of the ASK modulation circuit applied to the fourth embodiment of the present invention. In the ASK modulation circuit 100, the power amplification result of the power amplification circuit 81 is supplied to the first antenna 28A, and the variable attenuator 82 is connected to the second antenna that is electromagnetically coupled to the first antenna 28A. . Thereby, in the ASK modulation circuit 100, the electromagnetic field radiated from the first antenna 28A changes according to the transmission data string TX via the second antenna, and as a result, the ASK modulation signal is directed to the IC card. It is supposed to be emitted.

  According to the configuration shown in FIG. 15, even when the ASK modulation signal SM is generated by attenuating the power amplification result in the electromagnetic field on the output end side of the power amplifier circuit, the same effect as in the third embodiment can be obtained. it can.

  FIG. 16 is a block diagram showing the configuration principle of an ASK demodulation circuit applied to the fifth embodiment of the present invention. This ASK demodulation circuit 110 is applied in place of the ASK detection circuit 49 and the low-pass filter 50 of FIG. In addition, this Example 5 is not contained in this application, and is a reference example of this application to the last.

  The ASK demodulation circuit 110 receives the output signal SM of the loop antenna 28 via the coupling capacitor 111, and biases the output signal SM by a predetermined voltage VB from the resistor 112 and the DC power source 113. Here, as shown in FIG. 17, the bias value VB is set to such an extent that it is difficult to amplify the input signal by a half wave in the subsequent amplifier circuit 114. As a result, the ASK demodulation circuit 110 performs half-wave rectification on the response signal SM obtained via the loop antenna 28 by the amplifier circuit 114, and the ASK modulation signal, which is the response signal, is multiplied by the carrier wave and the side wave body. A baseband transform component of a wave body is generated. Thus, the baseband conversion component becomes the demodulated signal SD of the ASK modulated signal.

  On the other hand, if a limiter is arranged on the output side of the amplifier circuit 114 as shown in FIG. 18 and only a half wave of the response signal SM is amplified as shown in FIG. Components can be generated.

  The carrier removal circuit 118 removes the ASK modulation signal component from the output signal of the amplification circuit 114 formed by mixing the demodulated signal SD generated in this way, and outputs the result. In the configuration shown in FIG. 18, the ASK modulation signal component is removed from the output of the limiter 116.

  As this type of amplifier circuit 114, a transistor, an amplifier circuit using a field effect transistor, a differential amplifier circuit, or the like is applied. The carrier removal circuit 118 is applied with a low-pass filter, a band-pass filter, a trap filter, or the like according to the band of the demodulated signal SD.

  Specifically, the configuration shown in FIG. 20 is applied to the ASK demodulation circuit according to this embodiment. That is, in the ASK demodulation circuit 120, the output signal SM of the loop antenna 28 is input to the field effect transistor T5 via the coupling capacitor 121.

  Here, the field effect transistor T5 constitutes a common-source amplifier circuit having a drain resistance 124 with a gate voltage biased by a diode-connected field effect transistor T6 and resistors 122 and 123. As a result, the ASK modulation signal SM input to the gate of the field effect transistor T5 is biased by a predetermined voltage and amplifies only the positive direction of the input waveform.

  In the fifth embodiment, the ASK modulation signal can be demodulated with a simple configuration by amplifying the input signal by half a wave by setting the bias and removing the carrier component. As a result, it is possible to obtain a demodulation circuit that can be easily and easily integrated with other circuit blocks and can operate more efficiently.

  FIG. 21 in comparison with FIG. 20 is a block diagram showing an ASK demodulation circuit applied to the sixth embodiment of the present invention. In this ASK demodulator circuit 130, transistors T7 and T8 are used instead of the field effect transistors T5 and T6. The sixth embodiment is not included in the present application and is merely a reference example of the present application.

  According to the configuration shown in FIG. 21, even if transistors T7 and T8 are used instead of field effect transistors T5 and T6, the same effect as in the fifth embodiment can be obtained.

  FIG. 22 shown in comparison with FIG. 20 is a block diagram showing an ASK demodulation circuit applied to the seventh embodiment of the present invention. In the ASK demodulating circuit 140, the ASK modulation signal SM input via the coupling capacitor 121 is amplified by the grounded emitter type amplifier circuit including the resistors 131 to 133 and the transistor T9, and then input to the carrier removal circuit 118. In addition, this Example 7 is not contained in this application, and is a reference example of this application to the last.

  Further, the output signal of the grounded-emitter amplifier circuit is limited by a diode 134 disposed at the input terminal of the carrier removal circuit 118 and a limiter by the constant voltage power supply 135, so that the carrier removal circuit 118 receives only a half-wave amplification result. Input to convert sideband component to baseband component.

  According to the configuration shown in FIG. 22, even if the amplitude of the modulation signal is limited by a half wave on the output side of the amplifier circuit, the same effect as in the fifth embodiment can be obtained.

  FIG. 23 is a block diagram showing the configuration principle of an ASK demodulation circuit applied to the eighth embodiment of the present invention. The ASK demodulation circuit 150 is applied in place of the ASK detection circuit 49 and the low-pass filter 50 shown in FIG. The eighth embodiment is not included in the present application and is merely a reference example of the present application.

  The ASK demodulation circuit 150 receives the output signal SM of the loop antenna 28 via the coupling capacitor 121 and inputs this output signal SM to the clamp circuit 151. Here, the clamp circuit 151 clamps the input ASK modulation signal SM and gives waveform distortion to the ASK modulation signal SM. Thereby, the ASK demodulation circuit 150 converts the side wave component of the ASK modulation signal SM into a baseband component.

  Specifically, the configuration shown in FIG. 24 is applied to the ASK demodulation circuit according to this embodiment. That is, in the ASK demodulator circuit 150, the output terminal of the coupling capacitor 121 is grounded by the diode D having the reverse polarity, and the ASK modulation signal SM is clamped.

  According to the eighth embodiment, by limiting the amplitude of the ASK modulation signal, this amplitude limiting means can be created with a configuration suitable for integration into an integrated circuit by using a grounded type diode or the like. In addition, it is possible to obtain a demodulation circuit that can be simply and easily integrated and can operate more efficiently.

  FIG. 25 is a block diagram showing the configuration principle of an ASK demodulation circuit applied to the ninth embodiment of the present invention. The ASK demodulation circuit 160 is applied in place of the ASK detection circuit 49 and the low-pass filter 50 shown in FIG. The ninth embodiment is not included in the present application and is merely a reference example of the present application.

  In the ASK demodulation circuit 160, the ASK modulation signal SM is input to the amplification circuit 161, and ASK modulation signals SMA and SMB having the same phase and opposite phase are generated here. The ASK demodulating circuit 160 inputs these ASK modulated signals SMA and SMB to the clamp circuit 162 via the coupling capacitor 121, respectively, and clamps the ASK modulated signals SMA and SMB with substantially the same signal level, and these ASK modulated signals SMA. In addition, the same waveform distortion is given to SMB.

  The ASK demodulating circuit 160 inputs the ASK modulated SMA and SMB including the demodulated signal SD by applying waveform distortion in this way to the carrier removing circuit 118, where the signal components of the ASK modulated signals SMA and SMB are removed. To do. After that, the ASK demodulation circuit 160 inputs the output signal of the carrier removal circuit 118 to the addition circuit 163, and performs addition processing here, thereby adding the waveform distortion to the intermodulation component and the like that are included in the demodulation signal SD. Counter and remove. Note that the demodulated signal can be extracted efficiently by averaging instead of addition processing.

  Specifically, the configuration shown in FIG. 26 is applied to the ASK demodulation circuit 160 according to this embodiment. That is, in the ASK demodulation circuit 160, the ASK modulation signals SMA and SMB having the same phase and the opposite phase are clamped by the diode D, respectively.

  Further, the ASK demodulating circuit 160 adds the ASK modulation signals SMA and SMB whose amplitudes are limited in this way by an adding circuit having a non-inverting amplifier circuit configuration including resistors 164 to 166, a bias power source 167, and an operational amplifier circuit 168. The intermodulation component is canceled together with the ASK modulation signal component, and the demodulated signal component that is commonly included in the ASK modulation signals SMA and SMB is extracted by applying waveform distortion. Thereafter, the ASK demodulating circuit 160 limits the band by the carrier removing circuit 118 and outputs the demodulated signal SD.

  According to the ninth embodiment, an ASK modulated signal can be demodulated with a simple configuration by clamping an anti-phase ASK modulated signal to give waveform distortion and then adding and canceling out an undesired signal component. it can. As a result, it is possible to obtain a demodulation circuit that can be easily and easily integrated with other circuit blocks and can operate more efficiently.

  FIG. 27 is a block diagram of an ASK demodulation circuit applied to the tenth embodiment of the present invention. The ASK demodulation circuit 170 is applied in place of the ASK detection circuit 49 and the low-pass filter 50 shown in FIG. The tenth embodiment is not included in the present application and is merely a reference example of the present application.

  The ASK demodulator circuit 170 outputs the ASK modulation signal detected by the loop antenna 28 via a balanced transformer 171 in a balanced manner, so that the ASK modulation signal having the opposite phase can be obtained without using the amplifier circuit 161 described above with reference to FIG. Signals SMA and SMB can be generated.

  The ASK demodulating circuit 170 clamps one ASK modulation signal SMA by a clamp circuit using a diode D with the clamp potential set to the positive side and the negative side, respectively, and similarly clamps the clamp potential to the positive side and the negative side, respectively. The other ASK modulation signal SMB is clamped by a clamp circuit including a diode D set on the side.

  Further, the ASK demodulating circuit 170 adds the resistances of the ASK modulation signals SMA and SMB clamped by the positive-side clamp potential in a low-pass filter circuit including resistors 172 and 173 and a capacitor 174, and outputs the added output of the differential amplifier circuit 175. Input to the non-inverting input terminal. Similarly, in a low-pass filter circuit including resistors 176 and 177 and a capacitor 178, the ASK modulation signals SMA and SMB clamped with a negative-side clamp potential are resistance-added, and the addition output is the inverting input terminal of the differential amplifier circuit 175. To enter.

  As a result, the ASK demodulation circuit 170 cancels the ASK modulated signal component and extracts the demodulated signal component generated by clamping.

  The ASK demodulating circuit 170 band-limits the non-inverted output and the inverted output of the differential amplifier circuit 175 by the filters 179 and 180, respectively, thereby further removing the ASK modulation signal component, and then adding by the differential amplifier circuit 181. Output.

  According to the tenth embodiment, a balanced output is obtained from the antenna, and the ASK modulated signal is demodulated by clamping the balanced output and demodulating the ASK modulated signal, compared with the ninth embodiment. be able to.

  In addition, the ASK modulation signal can be processed more efficiently than in the ninth embodiment by clamping and processing each balanced output by a clamp circuit in which the clamp potential is set to the positive polarity side and the negative polarity side, respectively. In addition, the S / N ratio of the demodulation result can be improved.

  FIG. 28 is a block diagram showing the configuration principle of the ASK demodulation circuit applied to the eleventh embodiment of the present invention. The ASK demodulation circuit 190 is applied in place of the ASK detection circuit 49 and the low-pass filter 50 shown in FIG. The eleventh embodiment is not included in the present application and is merely a reference example of the present application.

  The demodulation circuit 190 determines the polarity of the ASK modulation signal SM in the polarity determination circuit 191, and multiplies the ASK modulation signal SM by the multiplication circuit 192 by multiplying the determination result by the ASK modulation signal SM. The same processing is executed. As a result, the demodulation circuit 190 demodulates the ASK modulation signal SM and outputs a demodulation signal SD.

  Specifically, the configuration shown in FIG. 29 is applied to ASK demodulation circuit 190 according to this embodiment. That is, in the ASK demodulating circuit 190, the ASK modulation signal SM is input to the inverting amplifier circuit 194 through the coupling capacitor 121. Here, the inverting amplifier circuit 194 outputs a polarity signal whose input level is switched to the positive side and the negative side according to the polarity of the ASK modulation signal SM by connecting the input terminal to the ground and the power supply line by the diode D. Thus, the polarity determination circuit 191 is configured by a limiter that limits the amplitude of the ASK modulation signal SM on the positive side and the negative side.

  The ASK demodulation circuit 190 multiplies the polarity signal by the ASK modulation signal SM in the multiplication circuit 192, and band-limits the multiplication result by the carrier removal circuit 118 to output the demodulation signal SD. Here, the multiplication circuit 192 is constituted by a double balanced mixer using a Gilbert multiplier.

  According to the eleventh embodiment, the polarity determination circuit determines the polarity of the ASK modulation signal, and multiplies the determination result by the ASK modulation signal, whereby the polarity determination circuit can be simply configured to demodulate the ASK modulation signal. be able to. As a result, it is possible to obtain a demodulation circuit that can be easily and easily integrated with other circuit blocks and can operate more efficiently.

  FIG. 30 is a block diagram showing the configuration principle of an ASK demodulation circuit applied to the twelfth embodiment of the present invention. The ASK demodulation circuit 200 is applied in place of the ASK detection circuit 49 and the low-pass filter 50 shown in FIG. This Example 12 is not included in the present application, and is merely a reference example of the present application.

  This demodulator circuit 200 determines the polarity of the ASK modulation signal SM in the polarity determination circuit 191 and selectively outputs the ASK modulation signal SM based on the determination result, thereby performing the full-wave rectification on the ASK modulation signal SM. The demodulation result is output.

  That is, the demodulation circuit 200 generates an ASK modulation signal SMA having the same phase as the ASK modulation signal SM and an ASK modulation signal SMB having an opposite phase to the ASK modulation signal SM in the amplification circuit 201. The demodulating circuit 200 intermittently outputs the ASK modulated signal SMB having the opposite phase based on the determination result of the polarity determining circuit 191 via the switch circuit 203. Further, based on the reverse polarity signal of the determination result obtained via the inverting amplifier circuit 204, the ASK modulation signal SMA having the same phase is intermittently output via the switch circuit 202, thereby depending on the polarity determination result, The ASK modulation signals SM and SMB are alternately output to full-wave rectify the ASK modulation signal SM.

  Specifically, in the ASK demodulating circuit 200 according to this embodiment, as shown in FIG. 31, a demodulated signal SD is output by generating a polarity signal by the same polarity determining circuit as described above with reference to FIG. .

  In this type of switch circuits 202 and 203, as shown in FIG. 32, a P-channel field effect transistor T10 and an N-channel field effect transistor T11 are connected in parallel, and the gate voltages of these transistors T10 and T11 are set. This can be realized by making complementary changes by the inverting amplifier circuit 206.

  According to the twelfth embodiment, the polarity determination circuit determines the polarity of the ASK modulation signal, and selectively outputs the ASK modulation signal based on the determination result, whereby the polarity determination circuit can be simply configured to perform ASK modulation. The signal can be demodulated. As a result, it is possible to obtain a demodulation circuit that can be easily and easily integrated with other circuit blocks and can operate more efficiently.

  In the above-described embodiment, the case where a modulated signal is generated using a carrier signal with a single frequency has been described. However, the present invention is not limited to this, and a rectangular wave signal with a single frequency is used instead of the carrier signal. Alternatively, a modulation signal may be generated by so-called double modulation using a phase modulation signal and a frequency modulation signal. When generating a modulation signal using a rectangular wave signal in this way, for example, the inverting amplification circuits 60 and 71 described in the first embodiment can be configured by an inverter.

  Furthermore, as a specific configuration in the above-described embodiment, the case where the output stage of the power amplifier circuit is configured by a field effect transistor has been described. However, the present invention is not limited to this, and may be configured by a bipolar transistor.

  In the above-described embodiments, the case where the variable attenuator is arranged on the output side of the power amplifier circuit has been described. However, the present invention is not limited to this, and the configuration of the power supply circuit is not limited thereto. The attenuator may be configured by switching the load on the output side of the power amplifier circuit in an equivalent manner by switching the impedance.

  Further, in the specific configuration in the above-described embodiment, the case where the power amplification result is attenuated by using the field effect transistor as the switching element has been described. However, the present invention is not limited to this, and the bipolar transistor and the PIN diode are used. These elements may be configured by, for example.

  Furthermore, in the above-described embodiment, the case where the IC card is operated by the power of the transmission signal has been described, but the present invention is not limited to this and can be widely applied to the case where the IC card is operated.

  Further, in the above-described embodiment, the case of modulating / demodulating transmission data by Manchester code has been described. However, the present invention is not limited to this, and when modulating / demodulating response data, and also for modulating / demodulating various codes other than Manchester code Furthermore, the present invention can be widely applied to amplitude modulation and demodulation of a multi-value data string, and further to amplitude modulation and demodulation of an analog signal such as an audio signal.

  In the above-described embodiment, the case where the present invention is applied to an IC card and a reader / writer is described. However, the present invention is not limited to this, and can be widely applied to various transmission apparatuses and reception apparatuses.

  The present invention can be applied to, for example, an IC card that inputs and outputs various data without contact and a reader / writer that performs data communication with the IC card.

It is a block diagram which shows the basic composition of the modulation circuit applied to the read / dryer based on Example 1 of this invention. It is a block diagram which shows the whole structure of an IC card system. FIG. 3 is a block diagram showing a modulation / demodulation circuit of the IC card system of FIG. 2. 2 is a chart for explaining the operation of the modulation circuit of FIG. 1. 2 is a time chart for explaining the operation of the modulation circuit of FIG. 1. FIG. 2 is a block diagram showing a specific configuration of the modulation circuit of FIG. 1. FIG. 7 is a connection diagram illustrating the power amplifier circuit of FIG. 6. 7 is a chart for explaining an operation of a control logic of the power amplifier circuit of FIG. 6. FIG. 4 is a block diagram showing a modulation circuit applied to a read / dryer according to a second embodiment of the present invention in comparison with FIG. 1. It is a block diagram which shows the basic composition of the modulation circuit applied to the reader / writer according to Example 3 of the present invention. It is a connection diagram with which it uses for description of the variable attenuator of FIG. FIG. 11 is a connection diagram for explaining a grounding type of the variable attenuator of FIG. 10. FIG. 13 is a connection diagram for explanation when the configuration shown in FIG. 11 and the configuration shown in FIG. 12 are combined in the variable attenuator of FIG. It is a block diagram which shows the specific structure of the modulation circuit of FIG. FIG. 11 is a block diagram illustrating a modulation circuit applied to a read / dryer according to a fourth embodiment of the present invention in comparison with FIG. 10. It is a block diagram which shows the basic composition of the demodulation circuit applied to the read driator concerning Example 5 of this invention. It is a characteristic curve figure with which it uses for description of the bias of the modulation signal in FIG. FIG. 17 is a block diagram showing a configuration in which a limiter is arranged instead of the bias in the configuration shown in FIG. 16. It is a characteristic curve figure with which it uses for description of the amplitude restriction | limiting in FIG. FIG. 17 is a block diagram showing a specific configuration of the demodulation circuit of FIG. 16. It is a block diagram which shows the demodulator circuit applied to the reader / writer based on Example 6 of this invention. It is a block diagram which shows the demodulator circuit applied to the reader / writer based on Example 7 of this invention. It is a block diagram which shows the basic composition of the demodulator circuit applied to the read / dryer based on Example 8 of this invention. FIG. 24 is a block diagram showing a specific configuration of the demodulation circuit in FIG. 23. It is a block diagram which shows the demodulation circuit applied to the reader / writer based on Example 9 of this invention. FIG. 26 is a block diagram illustrating a specific configuration of the demodulation circuit in FIG. 25. It is a block diagram which shows the demodulator circuit applied to the reader / writer based on Example 10 of this invention. It is a block diagram which shows the basic composition of the demodulation circuit applied to the reader / writer according to Example 11 of the present invention. FIG. 29 is a block diagram illustrating a specific configuration of the demodulation circuit of FIG. 28. It is a block diagram which shows the basic composition of the demodulator circuit applied to the reader / writer according to Embodiment 12 of the present invention. FIG. 31 is a block diagram showing a specific configuration of the demodulation circuit of FIG. 30. FIG. 32 is a connection diagram illustrating the switch circuit of FIG. 31. It is a block diagram which shows the modulation circuit using a variable gain amplifier circuit. It is a block diagram which shows the modulation circuit using a multiplication circuit. It is a block diagram which shows the demodulation circuit by the envelope detection using a diode. It is a block diagram which shows the demodulation circuit by phase synchronous detection. FIG. 36 is a schematic diagram illustrating a configuration in which the demodulation circuit of FIG. 35 is integrated. FIG. 38 is a connection diagram showing an equalization circuit having the integrated circuit configuration of FIG. 37.

Explanation of symbols

1, 3, 47, 55, 65, 80, 90 ... modulation circuit, 4, 10 ... multiplication circuit, 6, 8, 110, 120, 130, 140, 150, 160, 170, 190, 200 ... demodulation Circuit, D ... Diode, 21 ... IC card system, 22 ... IC card, 23 ... Leader, 28 ... Loop antenna, 48, 67, 68, 81, 92, 96 ... Power amplification circuit

Claims (8)

A variable attenuator for attenuating the power amplification result of the power amplification circuit according to an input signal at an output end of the power amplification circuit;
A modulation circuit that modulates an output signal of the power amplification circuit into an amplitude modulation signal corresponding to the input signal. The signal amplified by the power amplifier circuit is
The modulation circuit according to claim 1, wherein the modulation circuit is a single-frequency sine wave signal. The signal amplified by the power amplifier circuit is
The modulation circuit according to claim 1, wherein the modulation circuit is a single-frequency rectangular wave signal. The variable attenuator is
A first variable resistance means whose one end is held at a first potential and whose resistance value changes in response to a first control signal;
One end is connected to the other end of the first variable resistance means, the other end is held at a second potential different from the first potential, and a resistance value changes according to a second control signal. Variable resistance means;
The signal levels of the first and second control signals are switched according to the input signal and the control signal, and the potential at the connection midpoint of the first and second variable resistance means is changed to the first and second control signals. Switching to a potential corresponding to the potential, and control means for switching the impedance at the connection midpoint to a high impedance,
The modulation circuit according to claim 1, wherein the midpoint of connection is connected to an output terminal of the power amplifier circuit. 5. The modulation circuit according to claim 4, wherein the first and second variable resistance means are field effect transistors. The control means includes
6. The amplifier circuit according to claim 5, wherein signal levels of the first and second control signals are switched over to a voltage between a drain and a source of the field-effect transistor. In a transmitter having a modulation circuit based on amplitude modulation,
The modulation circuit is
A variable attenuator for attenuating the power amplification result of the power amplification circuit according to an input signal at the output end of the power amplification circuit;
A transmission apparatus that modulates an output signal of the power amplifier circuit into an amplitude-modulated signal corresponding to the input signal. In a transmission device that amplitude-modulates an input signal and transmits an amplitude-modulated signal,
A first modulation circuit for generating a first amplitude modulation signal in response to the input signal;
A second modulation circuit that generates a second amplitude modulation signal in which a phase of a carrier wave is inverted with respect to the first amplitude modulation signal in accordance with the input signal;
Arithmetic means for adding or subtracting the first and second amplitude modulation signals to generate the amplitude modulation signal;
The first modulation circuit comprises:
A variable attenuator for attenuating a power amplification result of the power amplification circuit according to the input signal at an output end of a power amplification circuit for amplifying a carrier;
Modulating the output signal of the power amplifier circuit into the first amplitude modulation signal corresponding to the input signal;
The second modulation circuit comprises:
A variable attenuator for attenuating a power amplification result of the power amplification circuit according to the input signal at an output terminal of a power amplification circuit for inverting and amplifying the carrier;
The transmission apparatus characterized by modulating the output signal of the power device circuit into the second amplitude modulation signal corresponding to the input signal.

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