JP2007142712A - High frequency apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high frequency apparatus capable of cutting off an unnecessary signal for saturating two reception circuits so as to attain downsizing by decreasing the number of chip inductors and excluding mutual effects in terms of high frequencies even when the two reception circuits are provided. <P>SOLUTION: The high frequency apparatus includes: a transmission circuit 101 for a mobile phone; and a digital broadcast reception circuit 103, and the digital broadcast reception circuit 103 includes the reception circuits for UHF and VHF. A notch filter 11 is provided to the input stage of the UHF reception circuit, and a low noise amplifier 12 is provided to the output stage of the notch filter 11. The ground terminal of the low noise amplifier 12 is connected to ground via collector-emitter of a transistor 15. Further, the other terminal of a first inductor 22 whose one terminal is connected to the input terminal of the notch filter 11 is connected to the input stage of the VHF reception circuit and the collector of the transistor 15. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a high-frequency device in which a digital broadcast reception signal is distributed and input to two reception circuits and a notch filter is provided at the input stage of one reception circuit.

  There has been proposed a mobile phone in which a digital broadcast receiving circuit is mounted in addition to a transmitting / receiving circuit for a mobile phone so that the digital broadcast can be received (see, for example, Patent Document 1). As shown in FIG. 4, a transmitting circuit 101 and a receiving circuit 102 for a mobile phone are mounted in the same casing 100 of the mobile phone, and a digital broadcast receiving circuit 103 is mounted. A transmitting circuit 101 and a receiving circuit 102 for a cellular phone are connected to an antenna 105 via an antenna switch 104, and a digital broadcast receiving circuit 103 is connected to another dedicated antenna 106.

  FIG. 5 is a circuit configuration diagram of a high-frequency device in which the mobile phone and the mobile TV described in Patent Document 1 are mounted in the same casing. The configuration on the mobile phone side will be described. In the reception circuit 102 for a cellular phone, a SAW (surface acoustic wave) filter 111 is connected to one terminal of an antenna switch 104, and an output of the SAW filter 111 is connected to a low noise amplifier 112. The output of the low noise amplifier 112 is connected to one input of the mixer 113. The output of the local oscillator 114 is connected to the other input of the mixer 113. The output of the mixer 113 is connected to a demodulator 115, and the output of the demodulator 115 is connected to an audio output device (speaker or receiver) 116. In the transmission circuit 101 for a mobile phone, the output of a sound input device (microphone) 117 that converts sound into an electric signal is connected to the modulator 118, and the output of the modulator 118 is connected to one input of the mixer 119. Connected. The other input of the mixer 119 is connected to the output of the local oscillator 114, and the output of the mixer 114 is connected to the power amplifier 120. The output of the power amplifier 120 is connected to the terminal of the antenna switch 104 through the low pass filter 121. A PLL circuit 122 is loop-connected to the local oscillator 114, and a data generator 123 is connected to the PLL circuit 122. The data generator 123 is connected to the PLL circuit 122 to change the reception and transmission frequency of the mobile phone.

  On the other hand, the configuration of the digital broadcast receiving circuit 103 is as follows. A high frequency amplifier 131 is connected to an antenna 106 to which a digital broadcast signal is input. The output of the high frequency amplifier 131 is connected to one input of the mixer 132. The other input of the mixer 132 is connected to the output of the local oscillator 133. The output of the mixer 132 is connected to the band pass filter 134, and the output of the band pass filter 134 is connected to one input of the mixer 135. The other input of the mixer 135 is connected to the output of the local oscillator 136. The output of the mixer 135 is connected to the band pass filter 137, and the output of the band pass filter 137 is connected to the demodulator 138. An image display (such as a liquid crystal display or a cathode ray tube) 139 is connected to the image output terminal of the demodulator 138, and an audio output device 140 is connected to the audio output terminal of the demodulator 138. A PLL circuit 141 is loop-connected to the local oscillator 133, and a PLL circuit 142 is loop-connected to the local oscillator 136. A data generator 143 is connected to the PLL circuits 141 and 142. The data generator 143 is connected to the PLL circuit 141 and the PLL circuit 142 to change the reception frequency (reception channel) of the portable television.

  The data generators 123 and 143 are connected to a data comparator 145 to compare data contents. The output is connected to the control unit 146, and based on the contents of the data comparator 145, data is output to the data generator 123 and the data generator 143 so that the mobile phone and the mobile TV do not interfere with each other. To. That is, both or one of the oscillation frequencies of the local oscillator 114 or the local oscillator 133 is changed by a minute amount.

  In the circuit configuration as described above, when the power output from the transmission circuit 101 for the mobile phone is +20 dBm or more and the isolation from the antenna 106 for receiving the digital broadcast signal is 10 dBm, the digital broadcast reception circuit The power of +10 dBm is input to 103. However, the input level of the digital broadcast signal input to the digital broadcast receiving circuit 103 is about −20 dBm at the maximum, and when the transmission power of the transmitting circuit 101 for the mobile phone is input to the receiving circuit 103 as it is, it is saturated. As a result, the digital broadcast signal cannot be received. In the case of a configuration in which the antenna 105 for the mobile phone and the antenna 106 for receiving the digital broadcast are shared, the transmission power directly flows from the transmission circuit 101 for the mobile phone to the digital broadcast reception circuit 103, so that the situation becomes more severe. .

  Therefore, conventionally, a notch filter for cutting the transmission power of the transmission circuit 101 for the mobile phone is provided at the input stage of the digital broadcast reception circuit 103. FIG. 6 is a diagram showing a circuit configuration provided in the input stage of the digital broadcast receiving circuit 103. As shown in the figure, the notch filter 150 for cutting the frequency of the transmission signal output from the transmission circuit 101 for the mobile phone, the low noise amplifier 151 for amplifying the signal output from the notch filter 150, and a higher frequency band than the UHF band. A low-pass filter 152 for removing frequency components is provided.

  FIG. 7 is a diagram showing frequency characteristics of the notch filter 150. The UHF band (470 MHz to 770 MHz) to be input to the digital broadcast receiving circuit 103 and the transmission frequency (830 MHz and / or 900 MHz) on the mobile phone side to be cut to prevent saturation are 100 MHz or less in the closest region. For this reason, the notch filter 150 is composed of a SAW filter 154. A first inductor 155 is provided between the input terminal of the SAW filter 154 and the ground, a second inductor 156 is provided between the ground terminal of the SAW filter 154 and the ground, and the output terminal of the SAW filter 154 is connected to the ground. A third inductor 157 is provided therebetween. These first to third inductors 155 to 157 match the impedance of the antenna 106 side and the receiving circuit 103 side. Further, the ground terminal of the low noise amplifier 151 is connected to the ground via the collector-emitter of the transistor 153. The base of the transistor 153 is connected to the LNA control terminal, and is controlled to perform an amplification operation and a through operation based on the ON / OFF signal. When the base of the transistor 153 is ON, the low noise amplifier 151 performs an amplification operation, and when the base is OFF, the low noise amplifier 151 performs a through operation.

By the way, digital radio broadcasting using 7/8 channels in the VHF band is currently planned. When a receiver circuit that receives a desired frequency in the VHF band is added to the digital broadcast receiver circuit 103 as shown in FIG. 4, the digital broadcast received signal is distributed to the UHF band and the VHF band. The signal distributed for the VHF band receives the desired channel by the processing circuit at the subsequent stage.
JP 2003-244015 A

  When the digital broadcast signal is distributed to the UHF band and the VHF band, it can be considered that the digital broadcast signal is distributed by a distribution circuit including a capacitor C and an inductor L as shown in FIG. That is, UHF band side and VHF band side receiving circuits are connected in parallel to the output terminal of the antenna, and a capacitor is placed in front of the notch filter 105 provided at the input stage of the UHF band side receiving circuit on the high band side. C is connected in series, and an inductor L is connected in series to the input stage of the receiving circuit on the VHF band side which is the low band side. The digital broadcast signal that has passed through the inductor L is input to the band-pass filter 160 to extract the VHF band (7 channels / 8 channels), and the extracted digital broadcast signal is output to the VHF tuner IC at the subsequent stage. Accordingly, since the signal for the VHF band is blocked by the capacitor C, it can be prevented from flowing to the ground side via the first inductor 155 and can be guided to the band-pass filter 160 on the VHF band side. On the other hand, since the signal for the UHF band is blocked by the inductor L, it can be prevented from flowing to the bandpass filter 160 on the VHF band side and can be guided to the notch filter 150 on the UHF band side.

  However, since the inductor L, which is a component of the distribution circuit, is large in size, there is a problem that it is difficult to reduce the size when the distribution circuit described above is provided.

  In addition, the transmitter circuit of the mobile phone and the digital broadcast receiver circuit (the receiver circuit for UHF and the receiver circuit for VHF) are not limited to being housed in the same casing, In a case where a notch filter is required to receive a received signal and cut an unnecessary frequency, the same problem as described above occurs.

  The present invention has been made in view of the above points, and can cut unnecessary signals that saturate the two receiving circuits, reduce the number of chip inductors, and reduce the size of the two receiving circuits. An object of the present invention is to provide a high-frequency device that can eliminate the influence of each other in a high-frequency manner and can realize a desired frequency characteristic even if it is provided.

  A high-frequency device according to the present invention receives a first frequency signal connected to an antenna and receiving a first frequency signal, and receives a second frequency signal connected to the antenna and having a frequency lower than that of the first frequency signal. A second receiving circuit; a notch filter provided between the antenna and the first receiving circuit; a low noise amplifier for amplifying a signal output from the notch filter; and a ground terminal of the low noise amplifier The notch filter includes a SAW filter having an input terminal connected to the antenna and an output terminal connected to the input terminal of the low noise amplifier, and one end of the SAW filter. An inductor connected to the input end of the filter, and the other end of the inductor is connected to the input end of the second receiving circuit and the low noise amplifier and the switch. Characterized in that it is connected to the connection point between the elements.

  According to this configuration, since the first receiving circuit is connected to the antenna via the notch filter, an unnecessary frequency signal that saturates the first receiving circuit can be cut by the notch filter. The receiving circuit can receive the first frequency signal. In addition, when the first frequency signal is received, the input terminal of the second receiving circuit is shunted via the switch element, which is equivalent to the fact that the second receiving circuit is not connected in terms of high frequency. Further, when the second frequency signal is received, the second receiving circuit is connected to the antenna through an inductor of a notch filter provided in the input stage of the first receiving circuit, so that an unnecessary frequency higher than that of the second frequency signal is obtained. The signal can be attenuated by the inductor, and the second frequency signal can be received by the second receiving circuit.

  In the high-frequency device, it is preferable that a connection point between the low noise amplifier and the switch element and the other end of the inductor are connected by a line, and a capacitor is provided on the line. Thereby, when the switch element is turned off, the DC voltage appearing at the connection point between the low noise amplifier and the switch element can be cut by the capacitor, and the deterioration of the characteristics of the second receiving circuit can be prevented.

  In the above high-frequency device, the switch element can be composed of a transistor.

  In the high-frequency device, a transmission circuit is provided adjacent to the first and second reception circuits, and the notch filter cuts a frequency of a signal output from the transmission circuit.

  According to this configuration, the frequency of the signal output from the adjacent transmission circuit can be cut by the notch filter and attenuated by the inductor, and the first and second reception circuits are saturated with the transmission signal of the transmission circuit. Can be prevented.

  In the high-frequency device, the first receiving circuit is a circuit that receives a UHF band signal, the second receiving circuit is a circuit that receives a VHF band signal, and the transmitting circuit is a portable device. It is a telephone transmission circuit.

  According to this configuration, the mobile phone casing contains the mobile phone transmission circuit, the first reception circuit that receives the UHF band signal, and the second reception circuit that receives the VHF band signal. However, it is possible to prevent the first and second reception circuits from being saturated with the transmission signal output from the transmission circuit of the mobile phone.

  In the high-frequency device, the first receiving circuit is a circuit for receiving a UHF band digital television signal, and the second receiving circuit is for receiving a VHF band 7-channel or 8-channel digital radio signal. It is a circuit for receiving.

  According to this configuration, since the number of inductors does not increase when a circuit for receiving digital radio signals of 7 or 8 channels in the VHF band is added, the size can be reduced.

  According to the present invention, in a high-frequency device that cuts a specific frequency with a notch filter, a reception signal can be input to two reception circuits without increasing the number of chip inductors, and the size can be reduced. Even if a receiving circuit is provided, it is possible to eliminate the influence of each other in terms of high frequency and realize a desired frequency characteristic.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
As shown in FIG. 4, a mobile phone transmitting circuit 101 and a receiving circuit 102 are mounted in a mobile phone casing 100 as shown in FIG. 4, and a UHF tuner IC and a second receiving circuit are used as a first receiving circuit. An example will be described in which a digital broadcast receiving circuit 103 ′ including a VHF tuner IC serving as a receiving circuit is mounted. Note that the transmitting circuit 101 and the receiving circuit 102 for the mobile phone are connected to the antenna 105 via the antenna switch 104, and the digital broadcast receiving circuit 103 'is connected to another dedicated antenna 106. The digital broadcast receiving circuit 103 'has a configuration in which a VHF tuner IC serving as a second receiving circuit is added to the digital broadcast receiving circuit 103 (UHF tuner IC) serving as the first receiving circuit shown in FIG. is there.

  FIG. 1 is a circuit configuration diagram of a portion that distributes a digital broadcast signal to a UHF tuner IC and a VHF tuner IC at the input stage of the digital broadcast receiving circuit 103 ′. The input terminal of the notch filter 11 is connected to the input / output terminal 10 of the antenna 106 for receiving digital broadcasting. The output terminal of the notch filter 11 is connected to the input terminal of the low noise amplifier 12. The output terminal of the low noise amplifier 12 is connected to the input terminal of the low-pass filter 13, and the output terminal of the low-pass filter 13 is connected to the input terminal 14 of the UHF tuner IC (103 in FIG. 5). The low noise amplifier 12 performs an amplification operation with an operating current flowing in a state where the ground terminal is electrically connected to the ground. The ground terminal of the low noise amplifier 12 is connected to the ground via the collector-emitter of the transistor 15. The base of the transistor 15 is connected to an LNA control terminal 16 to which a control signal for controlling the low noise amplifier 12 is applied.

  The notch filter 11 has the same configuration as the notch filter 150 shown in FIG. That is, the notch filter 11 includes a SAW filter 21 and first to third inductors 22 to 24, and has frequency characteristics shown in FIG. In the notch filter 11, one end of the first inductor 22 is connected to the input terminal of the SAW filter 21, a second inductor 23 is provided between the ground terminal of the SAW filter 21 and the ground, and the output terminal of the SAW filter 21. And a third inductor 24 is provided between the ground and the ground. These first to third inductors 22 to 24 function to match the impedances of the antenna 106 side and the digital broadcast receiving circuit 103 ′ side.

  FIG. 2 is a diagram illustrating a configuration example of the SAW filter 21. The SAW filter 21 includes four SAW resonators 40A to 40D. Two SAW resonators 40A and 40B are connected in series, the input end of the SAW resonator 40A on the input side is connected to the antenna input / output terminal 10, and the output end of the SAW resonator 40B on the output side is the low noise amplifier 12. Connected to input terminal. Further, a SAW resonator 40C is provided between the input end of the SAW resonator 40A on the input side and the ground, and a SAW resonator 40D is provided between the output end of the SAW resonator 40B on the output side and the ground. Yes. Since the SAW resonators 40A to 40D have the same circuit configuration, the configuration will be described using the SAW resonator 40A as an example. An inductor 41a (41b to 41d) and a capacitor 42a (42b to 42d) are connected in series, and a capacitor 43a (43b to 43d) is connected in parallel to the LC series circuit. That is, the SAW resonators 40A to 40D are configured by series-parallel resonant circuits. The constants of the SAW filter 21 configured as described above are adjusted so that the notch position comes near the transmission frequency (830 MHz or 900 MHz) of the mobile phone as shown in FIG.

  In the present embodiment, the other end of the first inductor 22 whose one end is connected to the input end of the SAW filter 21 is connected to the input terminal of the band pass filter 30 for extracting a desired channel signal in the VHF band. . In other words, the digital broadcast reception signal is distributed to the VHF tuner IC using the first inductor 22 of the notch filter 11. In this example, 7 and / or 8 channels are received as desired channels in the VHF band. The 7th and / or 8th channels of the VHF band are bands with a center frequency of 190 MHz. The bandpass filter 30 uses a SAW filter and has a passband characteristic with a center frequency of 190 MHz as shown in FIG. The output terminal of the band pass filter 30 is connected to the input terminal 31 of the VHF tuner IC.

  Further, in the present embodiment, the other end of the first inductor 22 is connected to the collector of the transistor 15 via the capacitor 25. When the transistor 15 is in the ON state, the input side of the bandpass filter 30 is short-circuited so that it can be equivalent to a state where there is no circuit on the VHF side in terms of high frequency.

Next, the operation of the present embodiment configured as described above will be described.
In the case of UHF band reception, a high level control signal is applied to the LNA control terminal 16, and the base of the transistor 15 is turned on. When the base of the transistor 15 is turned on, the other end of the first inductor 22 of the notch filter 11 is conductively connected to the ground via the capacitor 25 and the collector-emitter of the transistor 15. Accordingly, the other end of the first inductor 22 becomes conductive to the ground and the VHF side circuit connected via the other end of the first inductor 22 is shunted. The circuit is disconnected from the first inductor 22. As a result, the notch filter 11 is equivalent to the notch filter 150 shown in FIG. As a result, the transmission frequency that wraps around from the transmission circuit of the mobile phone can be cut in the same manner as the notch filter 150 (having the frequency characteristics shown in FIG. 7) shown in FIG.

  The digital broadcast reception signal in which the transmission frequency (830 MHz or 900 MHz) of the mobile phone is cut by the notch filter 11 is amplified by the low noise amplifier 12 controlled by the transistor 15 in the amplification operation state. The amplified signal output from the low noise amplifier 12 is input to the low-pass filter 13 and attenuated on the high frequency side of the UHF band and output to the UHF tuner IC at the subsequent stage. Since the UHF tuner IC cuts the transmission frequency (830 MHz or 900 MHz) of the mobile phone by the notch filter 11, it can receive a desired channel in the UHF band without being saturated with the transmission power.

  In the case of VHF band reception, a low level control signal is applied to the LNA control terminal 16, and the base of the transistor 15 is turned off. When the base of the transistor 15 is turned off, the low noise amplifier 12 enters a through operation state in which a signal input via the notch filter 11 is passed without being amplified. A direct current component appears on the collector side of the transistor 15 due to the signal flowing through the low noise amplifier 12, but can be cut by the capacitor 25. Thereby, it is possible to prevent a DC signal from flowing into the circuit on the VHF side via a line connecting the collector of the transistor 15 and the first inductor 22.

  If the base of the transistor 15 is OFF, the first inductor 22 is not grounded, so that the digital broadcast reception signal passes through the first inductor 22 and is input to the VHF side band-pass filter 30. As shown in FIG. 3, the band-pass filter 30 has a pass characteristic with the desired channel (190 MHz) in the VHF band as the center frequency. Therefore, the desired channel in the VHF band is extracted and output to the VHF tuner IC in the subsequent stage.

  At this time, since the transmission frequency (830 MHz or 900 MHz) of the mobile phone is extremely higher than the desired channel (190 MHz) in the VHF band, when the digital broadcast reception signal passes through the first inductor 22, High frequency signals including the transmission frequency (830 MHz or 900 MHz) are greatly attenuated. Accordingly, since the transmission frequency (830 MHz or 900 MHz) of the mobile phone can be attenuated by the first inductor 22, it is possible to prevent the VHF band circuit from being saturated with the transmission power on the mobile phone side and to receive a desired channel in the VHF band. It becomes.

  As described above, according to the present embodiment, the digital broadcast reception signal is distributed to the VHF side circuit using the first inductor 22 provided on the input end side of the notch filter 11. Without increasing the number of large chip inductors, it is possible to prevent large transmission power from being input to the circuit on the VHF side, and to prevent the digital broadcast receiving circuit (UHF receiving circuit and VHF receiving circuit) 130 'from being saturated. In addition to being able to reduce the size.

  Further, since the circuit on the VHF side is shunted when receiving the UHF band, it is the same as the UHF dedicated circuit in terms of high frequency, and better characteristics can be expected compared to a configuration in which a separate distribution circuit as shown in FIG. 8 is provided.

  Although the above description is an example in which the transmission circuit of the mobile phone and the digital broadcast reception circuit (the UHF reception circuit and the VHF reception circuit) are housed in the same casing, the present invention is suitable for such applications. It is not limited. The same applies to any circuit configuration in which reception signals are respectively input to two reception circuits adjacent to each other while unnecessary high frequency signals generated around the reception circuit are cut by a notch filter. is there.

  The present invention is applicable to a high-frequency device that distributes a digital broadcast reception signal and inputs it to two reception circuits and includes a notch filter at the input stage of one reception circuit.

The circuit block diagram of the part which distributes a digital broadcast signal to the tuner IC for UHF and the tuner IC for VHF in the high frequency apparatus which concerns on one embodiment of this invention Circuit diagram of the SAW filter shown in FIG. Characteristics diagram of the bandpass filter shown in FIG. Configuration explanatory diagram of a mobile phone in which a transmitter / receiver circuit for a mobile phone and a receiver circuit for receiving a digital broadcast are stored in the same housing FIG. 4 is a circuit configuration diagram of a mobile phone transmission / reception circuit and a digital broadcast reception circuit shown in FIG. Circuit configuration diagram of notch filter, etc. provided at the input stage of the receiving circuit for digital broadcast reception Characteristic diagram showing the relationship between UHF band and notch position by notch filter Circuit configuration diagram for distributing digital broadcast reception signal to UHF circuit and VHF circuit

Explanation of symbols

10 Digital Broadcasting Reception Antenna Input / Output Terminal 11 Notch Filter 12 Low Noise Amplifier 13 Low Pass Filter 14 UHF Tuner IC Input Terminal 15 Transistor 16 LNA Control Terminal 21 SAW Filter 22-24 First to Third Inductors 25 Capacitor 30 Band pass filter 40A to 40D SAW resonator 100 Mobile phone casing 101 Mobile phone side transmission circuit 102 Mobile phone side reception circuit 103 Digital broadcast reception circuit 105 Mobile phone side antenna 106 Digital broadcast reception antenna

Claims (6)

A first receiving circuit connected to an antenna for receiving a first frequency signal; a second receiving circuit connected to the antenna for receiving a second frequency signal having a frequency lower than the first frequency signal; A notch filter provided between the antenna and the first receiving circuit; a low noise amplifier for amplifying a signal output from the notch filter; and provided between a ground terminal of the low noise amplifier and the ground. Switch element provided,
The notch filter includes a SAW filter having an input end connected to the antenna and an output end connected to the input end of the low noise amplifier, and an inductor having one end connected to the input end of the SAW filter,
A high-frequency device, wherein the other end of the inductor is connected to an input end of the second receiving circuit and is connected to a connection point between the low-noise amplifier and the switch element.   The high-frequency device according to claim 1, wherein a connection point between the low noise amplifier and the switch element and the other end of the inductor are connected by a line, and a capacitor is provided on the line.   3. The high-frequency device according to claim 1, wherein the switch element includes a transistor.   4. The transmitter circuit according to claim 1, wherein a transmitter circuit is provided adjacent to the first receiver circuit and the second receiver circuit, and the notch filter cuts a frequency of a signal output from the transmitter circuit. A high-frequency device according to any one of the above. The first receiving circuit is a circuit that receives a UHF band signal;
The second receiving circuit is a circuit that receives a VHF band signal,
5. The high frequency device according to claim 4, wherein the transmission circuit is a transmission circuit of a mobile phone. The first receiving circuit is a circuit that receives a digital television signal in the UHF band,
6. The high-frequency device according to claim 1, wherein the second receiving circuit is a circuit that receives a digital radio signal of 7-channel and / or 8-channel in the VHF band.

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