JP3672913B2 - Oscillation frequency correction circuit for portable radio - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a circuit of a voltage-controlled temperature-compensated crystal oscillator that can control the oscillation frequency of a reference oscillator of a portable radio device.
[0002]
[Prior art]
Conventional radio equipment inputs modulation signals to both the VCO and the reference oscillator, compensates for the low frequency components attenuated by the modulation of the VCO with the modulation of the reference oscillator, and keeps the modulation frequency characteristics constant from low to high. Thus, even in the case of a rectangular waveform having a low-frequency component and a high-frequency component, distortion generated in the modulation waveform is suppressed (see, for example, Patent Document 1).
[0003]
[Patent Document 1]
JP-A-11-284524 (2nd page, 2nd column, FIG. 7)
[0004]
FIG. 2 is an explanatory diagram used in the past, and is a voltage-controlled oscillator (hereinafter referred to as “VCO”; Voltage Controlled Oscillator) 1 and a PLL integrated circuit (hereinafter referred to as “PLL-IC”; Phase Locked Loop IC). ) 2, a voltage-controlled temperature-compensated crystal oscillator (hereinafter referred to as “VC-TCXO”; Voltage Controlled-Temperature Compensated Crystal Oscillator) 3, and a control circuit (I) 6 and a frequency adjustment circuit 8.
When this circuit is used as an FM modulation type transmission modulation circuit, an analog audio signal or digital data signal input as a modulation signal (signal <1>) is subjected to signal <4 after its DC component is cut by a capacitor. Is input from the point b to the VCO 1 and from the point (d) to the VC-TCXO 3. In the VC-TCXO3, the modulation signal is modulated in the low frequency band, and the output signal <3> is input to the PLL-IC2 from the point a, and the signal <2> is output from the PLL-IC2. Superimposed.
Control as a frequency synthesizer is performed in a looped circuit of the VCO 1, a control circuit (I) 6 to which an automatic or manual channel control signal is input from the outside, and the PLL-IC 2. (Signal <6>) is obtained. At the same time, the modulation signal <4> is input to the VCO 1 at the point b, and the VCO 1 performs modulation in the high frequency band of the modulation signal input (signal <1>).
[0005]
The modulation signal input (signal (1)) is mainly a signal band of 300 Hz to 3 KHz in the case of communication with an analog audio signal, that is, a high frequency modulation frequency band of 300 Hz or more. In the case of a digital data signal, for example, It becomes a binary rectangular wave of 4800 bps or 9600 bps, and a modulation frequency band from a low frequency of 300 Hz or lower to a high frequency of 300 Hz or higher is required, and one of these two signals is input to the modulation signal (1) Is entered as As described above, a wideband modulated transmission carrier (signal (6)) having both high and low frequency bands can be obtained by a set of circuits of VCO1 and VC-TCXO3.
[0006]
FIG. 3 shows a modulation characteristic diagram of the conventional circuit of FIG. First, as a characteristic on the VCO 1 side, that is, in a case where the line of the signal (4) inputted to the VC-TCXO3 side is not connected and the signal (4) is inputted only to the VCO 1, the modulation is performed. It has a characteristic curve indicated by a point, and the modulation of the frequency band of the modulation signal of 300 Hz or higher is performed. Here, the modulation sensitivity is lower as the frequency band of the modulation signal is lower. This covers the entire band of speech and the high frequency components of digital data as modulation characteristics.
On the other hand, in the modulation on the VC-TCXO3 side, when the signal (4) line supplied to the VCO1 side is not connected and the signal (4) is input only to the VC-TCXO3, the modulation is indicated by the black circle point. This is a curve, which is modulated in the frequency band of a modulation signal of 300 Hz or less, and has a characteristic that the modulation sensitivity is lower as the frequency band of the modulation signal is higher. Here, a frequency band close to a DC component which is a low frequency component of digital data is covered as a modulation characteristic.
Therefore, a flat characteristic is obtained from a low frequency near 20 Hz to a high frequency near 5 KHz as a characteristic obtained by combining both characteristic curves. This coalescence characteristic curve has a flat characteristic from a low frequency range to a wide frequency range like a characteristic curve indicated by a black triangle point, and can cope with modulation of a digital data rate of 4800 bps to 9600 bps as well as a voice frequency band.
[0007]
Also, the operation of the transmission carrier oscillation circuit according to FIG. 2 is performed by using VC-TCXO3 as a reference oscillator and inputting the output a point (signal {circle around (3)}) to PLL-IC2 and output of PLL-IC2 (signal {circle around (2)}). The synthesizer circuit generates a frequency according to the voltage of ▼) by the VCO1, and the VCO1 generates a carrier wave (signal (6)) of the transmission signal. In this way, the PLL-IC 2 and the VCO 1 are combined, the transmission channel frequency is controlled by the channel frequency control signal from the control circuit (I) 6, and the transmission channel frequency is automatically or manually set to an arbitrary transmission channel frequency. As an example in the VHF band, the carrier wave (signal (6)) when the signal (2) is 1.0V is 136.000 MHz, and similarly the carrier wave (signal (6)) is 2.0V and the signal (2) is 2.0V. 155.000 MHz, signal (2) is 3.0 V, and the carrier wave (signal (6)) is 174.000 MHz.
2. VC-TCXO3 in the conventional circuit is a fixed reference frequency oscillator set by the frequency adjustment circuit 8, and is frequency-modulated according to the input level of the modulation signal (signal (4)). The modulation component is output in the form of a synthesized reference frequency oscillation, which is the reference frequency of the PLL-IC2. As an example, when the signal (4) input to the VC-TCXO3 is 2.5V, 19.2 MHz is output as the signal (3), and the change of the modulation signal voltage is 10 ppm / V. Have
Regarding frequency synthesis as a circuit synthesizer, first, the output frequency (carrier frequency) signal (6) of VCO1 is equal to 1 / N times the output frequency of VC-TCXO3 and 1 / M times the output frequency of VCO1. From this frequency relationship, the output frequency of VCO 1 is obtained. The values of M and N are input to the PLL-IC 2 as a channel frequency control signal from the control circuit (I) 6, and the channel frequency is set. For example, if the output frequency of VC-TCXO3 as a reference frequency oscillator is 19.2 MHz, N = 10, M = 100 and PLL-IC2 are set, and the output frequency signal {circle around (6)} of VCO1 is 192 MHz as the transmission carrier frequency. It becomes.
[0008]
In the transmission circuit, when the radio is in the transmission mode and the conventional circuit in FIG. 2 is in the reception mode, the modulation signal input (signal (1)) is in the input OFF state, and the output signal of the VCO 1 (signal (6)). ▼) is supplied to the receiving circuit as a local oscillation frequency signal of a superheterodyne receiver.
That is, the conventional circuit shown in FIG. 2 is also used as a local oscillator for receiving radio frequency. In this case, the modulation signal (signal 6) is off, and VC-TCXO3 operates as a fixed single frequency reference oscillator. Then, the output is input to the PLL-IC 2, and the PLL-IC 2 is combined with the VCO 1 and the reception channel frequency is controlled by the channel frequency control signal from the control circuit (I) 6. Set to frequency.
[0009]
[Problems to be solved by the invention]
However, in the conventional circuit, the frequency deviation of VC-TCXO is not automatically or manually controlled after the initial setting by the frequency adjustment circuit 8. Therefore, in the conventional portable wireless device, the frequency accuracy remains as much as the initial deviation of the transmission and reception frequencies or the deviation over time, and in a data transmission system that requires high frequency accuracy, VC There was a problem that it could not be used stably as a reference oscillator unless fine correction was made to the oscillation frequency of TCXO.
[0010]
An object of the present invention is to provide a portable wireless device having a circuit capable of modulating both an analog audio signal and a digital data signal, and capable of being used in a data transmission system that requires high frequency accuracy. An object of the present invention is to provide an oscillation frequency correction circuit in a radio device.
[0011]
[Means for Solving the Problems]
The oscillation frequency correction circuit in the portable radio of the present invention is a portable radio that uses a voltage-controlled crystal oscillator as a reference oscillator.
A first control circuit for channel selection is provided in the phase control loop of the voltage controlled oscillator controlled by the P LL-IC so as to have a frequency synthesizer function, and the oscillation frequency of the voltage controlled oscillator can be controlled by a modulation input signal. A voltage controlled oscillation circuit configured to be modulated at a high frequency in a frequency band;
Oscillation frequency of the crystal oscillator comprises a crystal oscillator, the modulation input signal modulating low frequency is made is a voltage controlled given as a reference frequency before Symbol P LL-IC oscillation output which is the modulation in the audio frequency band by Crystal oscillator,
A second control circuit that outputs a stepped frequency deviation control DC signal by an automatic or manual control input that is an RSSI output voltage of a received signal or a bit error rate of received data ;
An operational amplifier circuit in which the low frequency modulation and the frequency deviation control are simultaneously performed by superimposing the frequency deviation control DC signal as a differential input of the modulation input signal;
The reference oscillation frequency of the voltage controlled crystal oscillator is corrected by adjusting the frequency deviation control DC signal, whereby the oscillation frequency of the voltage controlled oscillator is finely adjusted to a predetermined channel oscillation frequency ,
Solved the problems by providing what the none of the analog audio signals and digital data signals of the audio frequency band is configured so that to said modulated input signal.
[0012]
[Action]
The operation of the present invention is such that the oscillation frequency of the VC-TCXO is finely controlled by the frequency deviation control signal output from the second control circuit.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
As shown in FIG. 1, the embodiment of the present invention includes VCO1, PLL-IC2, VC-TCXO3, operational amplifier (I) 4, operational amplifier (II) 5, control circuit (I) 6, control circuit (II ) 7.
As an FM modulation transmission circuit, first, either an analog audio transmission signal or a digital data transmission signal is input to the operational amplifier (I) 4 as a modulation signal input (signal {circle around (1)}), and its output is output. The point b of the signal {circle over (5)} is input to the VCO 1 and at the same time is input to the operational amplifier (II) 5, and the output of the operational amplifier (II) 5 is input to the VC-TCXO 3 as the signal {circle around (4)} (d). Is done.
The VCO 1 performs modulation in the high frequency band (about 300 Hz or more) by the point b of the signal (5) input to the VCO 1 from the operational amplifier (I) 4. Modulation in the low frequency band (about 300 Hz or less) is performed by the point a of the signal (4) input from the output of the operational amplifier (II) 5 to the VC-TCXO 3.
By performing the modulation of the above two bands, it is possible to perform frequency modulation from low frequencies to high frequencies in the vicinity of DC of the input modulation signal. It is possible to modulate both of the digital data signals using the band.
[0014]
Further, in the circuit configuration of FIG. 1, it also functions as a carrier circuit for a transmission frequency, and the point c of the frequency deviation control signal (signal (7)) for controlling the oscillation frequency of the reference oscillator of the radio frequency is an operational amplifier ( I) The reference voltage of 4 and the operational amplifier (II) 5 is input to both operational amplifiers. As a result, the DC voltage component at the point (d) of the signal {circle around (4)} which is the output of the operational amplifier (II) 5 becomes a voltage component as frequency deviation control.
The frequency deviation control signal is the point c of the signal (7) output from the control circuit (II) 7 and a voltage of arbitrary resolution is automatically or manually divided into 0 to 5 V in 1024 steps as the frequency deviation control signal. Output.
By changing the DC voltage, which is a frequency deviation control signal, the carrier frequency in the oscillation circuit of VC-TCXO3 and VCO1 can be finely adjusted to an arbitrary frequency automatically or manually with respect to the transmission channel frequency.
To adjust the frequency of the output frequency (signal (6)) from the VCO 1, first, the modulation signal input (signal (1)) is disconnected and both the VC-TCXO3 and VCO1 are left unmodulated. (Signal {circle over (6)}) is measured, and when there is a frequency deviation from the desired carrier frequency, the voltage of the frequency deviation control signal (signal {circle over (7)}) is step-adjusted to match the predetermined carrier frequency. .
[0015]
1 is the output of the control circuit (II) 7 because the output frequency of the VC-TCXO 3 is determined with the frequency of the specification value as the standard, as the frequency synthesis relationship of the frequency synthesizer of the inventive circuit. The voltage of the frequency deviation control signal (signal {circle around (7)}) is adjusted so that the output frequency of the VC-TCXO3 becomes a specified value frequency. For example, when the control voltage DC2.5V of the frequency deviation control signal (signal (7)), even if the oscillation frequency (signal (3)) is a specification value of 19.2 MHz, sometimes the control voltage Some devices have an oscillation frequency (signal (3)) of 19.2 MHz at 2.3 V, and other devices have an oscillation frequency (signal (3)) of 19.2 MHz at a control voltage of 2.7 V.
Therefore, the VC-TCXO3 oscillation circuit according to the present invention can be finely adjusted independently with the stepping voltage of the frequency deviation control signal (signal (7)). Usually, the input step voltage of the frequency deviation control signal (signal (7)) after being set once maintains a predetermined DC voltage.
The step voltage of the frequency deviation control signal (signal (7)) is input to the (−) side terminal by being input to the (+) side terminal of the operational amplifier (I) 4 and the operational amplifier (II) 5. The signal is synthesized by differential amplification with the modulation signal input (signal (1)). The signal (4) input to the VC-TCXO3 side is obtained by superimposing the modulation signal on the VC-TCXO3 side on the step voltage of the frequency deviation control signal (signal (7)), and the control circuit ( II) The frequency is arbitrarily controlled automatically or manually from 7. In this way, it is suitable for digital communication such as data transmission that requires high accuracy carrier frequency stability and high modulation accuracy.
[0016]
Next, the circuit configuration of FIG. 1 also functions as a local oscillation frequency generating circuit in the reception mode. In this case, the modulation signal (signal 6) is set to an input “none” state. First, the frequency deviation control signal (signal (7)) is input as a reference voltage for the operational amplifier (I) 4 and the operational amplifier (II) 5. Next, the DC voltage component of the output of the operational amplifier (II) 5 is the control voltage, and the DC of the frequency deviation control signal (signal (7)) input from the control circuit (II) 7 and the output of the operational amplifier (I) 4 is output. This is a differential amplification output with a voltage component as an input, and becomes a frequency deviation control signal having a constant DC value.
The frequency deviation control signal (signal (7)) is an output of the control circuit (II) 7 (for example, a microprocessor), and outputs an arbitrary step voltage automatically or manually while dividing 0 to 5 VDC into 1024 steps. I can do it.
By changing and adjusting the DC voltage of the frequency deviation control signal (signal (7)), the reception frequency can be automatically or manually adjusted to an arbitrary frequency.
The frequency generation principle (relationship between M value and N value) as a synthesizer by the PLL-IC 2, the VCO 1, and the control circuit (I) 6 is the same as that of transmission.
As frequency deviation control when a frequency difference occurs between the frequency of the received signal and the reception frequency set in the radio device, the frequency difference is detected by a predetermined means, and only the frequency difference is detected by the radio device. The oscillation frequency of the VC-TCXO 3 is finely adjusted by the frequency deviation control signal (signal {circle around (7)}) which is the output of the control circuit (II) 7 which can correct the reception frequency set to ## EQU3 ## The output frequency of VCO 1 can be matched with the frequency of the received signal as the local oscillation frequency.
[0017]
By receiving the transmission frequency from the base station, detecting the reception frequency deviation, and obtaining the frequency deviation control signal of a value finely adjusted to correct the deviation, the transmission and reception of the portable radio The frequency can be matched to the transmission frequency of the base station.
An example of means for detecting this frequency deviation is to correct the frequency deviation using the RSSI function (Received Signal Strength Indicator; which outputs a voltage proportional to the electric field level of the received signal) of the receiver. The RSSI output voltage is monitored while changing the frequency deviation control signal, and when the RSSI output voltage is the highest, the frequency deviation is the smallest. Therefore, the RSSI output voltage is changed while the frequency deviation control signal is changed. Is fixed at the highest voltage.
As another example of means for detecting a frequency deviation, in the case of receiving a digital data signal, the bit error rate of the pattern is monitored inside the radio at a specific pattern such as a synchronization signal in the received signal. The error rate is monitored while changing the frequency deviation control signal, and when the error rate is the smallest, the frequency deviation is the smallest. It is fixed to the voltage when the error rate is the smallest.
[0018]
【The invention's effect】
As described above, according to the invention described in claim 1, since modulation is performed by both the VCO and the VC-TCXO, it has a flat frequency characteristic with a small deviation from a low frequency to a high frequency. A high-accuracy frequency modulation circuit for both the digital data signals is provided. If such a circuit is used, a reference voltage is supplied to the VC-TCXO through each operational amplifier, and the frequency of the VC-TCXO is controlled, which controls the frequency deviation between the transmission carrier frequency and the reception local oscillation frequency, and It has a fine-tuning frequency correction effect that matches the reception frequency to the transmission frequency with deviation, so it is extremely useful as a portable radio device suitable for digital data transmission that requires high-precision frequency. The effect is great.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating an example of a modulation circuit of a portable radio device according to the present invention.
FIG. 2 is a block diagram showing a modulation circuit of a conventional portable radio device.
FIG. 3 is a characteristic diagram showing a modulation characteristic of a modulation circuit of a conventional portable radio device.
[Explanation of symbols]
1 VCO
2 PLL-IC
3 VC-TCXO
4, 5 operational amplifier (I, II)
6, 7 Control circuit (I, II)
8 Frequency adjustment circuit

Claims (1)

In a portable radio using a voltage controlled crystal oscillator as a reference oscillator,
A first control circuit for channel selection is provided in the phase control loop of the voltage controlled oscillator controlled by the P LL-IC so as to have a frequency synthesizer function, and the oscillation frequency of the voltage controlled oscillator is controlled by a modulation input signal. A voltage controlled oscillation circuit configured to perform high-frequency modulation in a frequency band;
Oscillation frequency of the crystal oscillator comprises a crystal oscillator, the modulation input signal modulating low frequency is made is a voltage controlled given as a reference frequency before Symbol P LL-IC oscillation output which is the modulation in the audio frequency band by Crystal oscillator,
A second control circuit that outputs a stepped frequency deviation control DC signal by an automatic or manual control input that is an RSSI output voltage of a received signal or a bit error rate of received data ;
An operational amplifier circuit that simultaneously performs the modulation of the low frequency and the frequency deviation control by superimposing the frequency deviation control DC signal as a differential input of the modulation input signal;
By adjusting the frequency deviation control DC signal, the oscillation frequency of the voltage controlled oscillator is finely adjusted to a predetermined channel oscillation frequency by correcting the reference oscillation frequency of the voltage controlled crystal oscillator .
Oscillation frequency correction circuit in a portable radio apparatus of any of the analog audio signals and digital data signals of the audio frequency band are configured to the modulated input signal and to so that.

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