JP6449683B2 - Tuning circuit for radio - Google Patents

Description

  The present invention relates to a tuning circuit in a radio receiver, and more particularly to a tuning circuit for a radio that can eliminate the need for individual settings based on individual differences during manufacturing, improve productivity, and maintain good characteristics.

[Description of Prior Art: FIG. 5]
A tuning circuit using a voltage controlled frequency variable band pass filter (VCF) in a conventional radio receiver will be described with reference to FIG. FIG. 5 is a schematic circuit diagram of a conventional tuning circuit.
As shown in FIG. 5, the conventional tuning circuit includes an input terminal 31, an output terminal 32, a VCF 33, a ROM (Read Only Memory) 34, and a D / A (Digital / Analog) converter 35. Yes.

Each part of the conventional tuning circuit will be described.
The input terminal 31 inputs a radio signal.
The output terminal 32 outputs a radio signal that has passed through the VCF 33.
The VCF 33 band-limits the input signal according to the control voltage, and allows a radio signal having a specific frequency to pass therethrough.
The ROM 34 stores voltage data corresponding to the frequency to be passed at an address set from the outside, and outputs voltage data at the address.
The D / A converter 35 D / A converts the voltage data from the ROM 34 to generate a control voltage and outputs it to the VCF 33.

The operation of the conventional tuning circuit will be described.
In the conventional tuning circuit, voltage data corresponding to the address set from the ROM 33 is output.
The voltage data is D / A converted by the D / A converter 34 and output to the VCF 33 as a control voltage. The VCF 33 limits the band of the input signal from the input terminal 31 with a pass band corresponding to the control voltage, passes a radio signal of a desired frequency, and outputs it to the output terminal 32.
In this way, the operation of the conventional tuning circuit is performed.

Here, there are variations in characteristics of the variable capacitance diode and the inductor of the analog element used in the VCF 33 of the conventional tuning circuit.
Therefore, at the time of production of the tuning circuit, it is necessary to acquire control voltage data corresponding to a desired frequency one by one according to the characteristics of each VCF 33 and write the control voltage data individually to the ROM 34.

  Further, in the conventional tuning circuit, since the control voltage is generated using the control voltage value written in the ROM 34, the control voltage cannot be adjusted in accordance with the temperature characteristics and aging of the variable capacitance diode and the inductor. Characteristics may vary.

[Related technologies]
In addition, as a technique regarding the tuning circuit of the wireless device, Japanese Patent Application Laid-Open No. 2001-36384 “Variable Tuning Filter and Adjustment Method and Receiving Device and Transmitting Device Using the Same” (Matsushita Electric Industrial Co., Ltd., Patent Document 1), Japanese Unexamined Patent Application Publication No. 2007-174743 “YIG Filter Tuning System” (Agilent Technologies, Inc., Patent Document 2), Japanese Unexamined Patent Application Publication No. 2012-202760, “Filter Calibration Device and Calibration Method” (Anritsu Corporation, Patent Document 3). is there.

  Patent Document 1 describes that in a variable tuning filter, the CPU controls the center frequency of the band-pass filter and the gain of the variable gain amplifier by a control signal stored in the storage means in response to a change in tuning frequency. Yes.

  In Patent Document 2, in a YIG (Yttrium Iron Garnet) filter tuning system, when a noise source is coupled to the input of the filter, a receiver is coupled to the output of the filter. The acquisition of a series of measurements in a band is described.

  In Patent Document 3, the signal from which the noise from the noise generator has passed through the YIG tuning filter unit is used as a calibration signal, the calibration signal is analyzed as a reference frequency signal, and the frequency signal and the reference frequency signal are compared. It describes that the amount of deviation is calculated and the center frequency of the tunable filter is adjusted and controlled so as to cancel out the amount of deviation.

JP 2001-36384 A JP 2007-174463 A JP 2012-202760 A

  As described above, in the conventional tuning circuit, in order to absorb the individual difference of the components in the VCF, it is necessary to obtain an appropriate control voltage value for each unit and write it into the ROM, and the writing operation is complicated. In addition, there is a problem that the control voltage of the VCF cannot be adjusted in accordance with the temperature characteristics of the parts and the secular change.

  In Patent Documents 1 to 3, white noise is input to the VCF, a coarse adjustment control voltage is applied, a radio signal after passing through the VCF is converted to an intermediate frequency signal, and the peak is detected. The voltage is held, the coarse control voltage is turned off, the reference voltage and the detection voltage are compared with a comparator to obtain a differential voltage, and a voltage obtained by adding the differential voltage to the coarse control voltage is generated as the fine control voltage. That is not described.

  The present invention has been made in view of the above circumstances, and eliminates the need for writing control voltage values for each unit based on individual differences, improving production efficiency, and responding to temperature characteristics and aging of parts. An object of the present invention is to provide a radio tuning circuit capable of adjusting a control voltage and maintaining good characteristics.

The present invention for solving the problems of the above-described conventional example is a tuning circuit of a radio device, an input terminal for inputting a radio signal, a signal generator for generating white noise, and an input signal according to a control voltage The first switching is performed so that either a voltage control filter that passes a specific frequency and outputs the signal, or a radio signal input to the input terminal or white noise generated by the signal generator is input as an input signal of the voltage control filter. A switch for storing the coarse adjustment control voltage value corresponding to a specific frequency, a D / A converter for D / A converting the coarse adjustment control voltage value and outputting the coarse adjustment control voltage, and a coarse adjustment A second switch that switches whether or not to input the control voltage as a control voltage to the voltage control filter, a frequency converter that converts an output signal from the voltage control filter into an intermediate frequency, a frequency change A detector for detecting output signals from the section, the maximum value of the output voltage from the detection wave unit holding as a reference value, a peak hold circuit for outputting a reference voltage based on the reference value, the output voltage from the detector And a reference voltage from the peak hold circuit are input and compared, and a differential voltage is added to a voltage corresponding to the coarse control voltage to output a fine control voltage, and a fine control output from the comparator A hold circuit that holds the control voltage value and outputs a fine control voltage based on the value, and a fine control voltage from the comparator is input as the control voltage of the voltage control filter, or a fine control voltage from the hold circuit. And a third switch for switching between input of the control voltage and not input of both, and after the tuning operation using white noise is started, the maximum value of the output voltage from the detector is used as a reference value. Pi First specific period until it is held in Kuhorudo circuit, the first switch is switched to enter the white noise generated by the signal generator, a second switch, as the control voltage of the voltage control filter is switched to enter the coarse tuning control voltage from D / a converter, the third switch is switched et not to enter both the fine adjustment control voltage from fine adjustment control voltage and hold circuit from the comparator It is characterized by that.

According to the present invention, in the tuning circuit, after the first specific period, the second specific until the differential voltage between the output voltage from the detector and the reference voltage from the peak hold circuit is stabilized in the comparator. During the period, the first switch is switched to input the white noise generated by the signal generator as an input signal to the voltage control filter, and the second switch supplies the coarse control voltage from the D / A converter. the switched so as not to input to the voltage controlled filter, the third switch, and wherein the switching et Reruko to enter the fine adjustment control voltage from the control voltage and the specific較器of said voltage controlled filter.

According to the present invention, in the tuning circuit, after the second specific period, during the period of operation by inputting a radio signal, the first switch uses the radio signal from the input terminal as an input signal as a voltage control filter. The second switch is switched so as not to input the coarse control voltage from the D / A converter to the voltage control filter, and the third switch is held as the control voltage of the voltage control filter. It is characterized in the changeover et Reruko to enter the fine adjustment control voltage from the circuit.

According to the present invention, an input terminal for inputting a radio signal, a signal generator for generating white noise, a voltage control filter for passing a specific frequency according to a control voltage for the input signal and outputting the input signal, and an input terminal A first switch that switches to input either an input radio signal or white noise generated by a signal generator as an input signal of the voltage control filter, and stores a coarse control voltage value corresponding to a specific frequency A storage unit; a D / A converter that D / A converts a coarse control voltage value and outputs a coarse control voltage; and a first switch that switches whether the coarse control voltage is input to the voltage control filter as a control voltage. and second switch, a frequency conversion unit for converting an output signal from the voltage-controlled filter to the intermediate frequency, and a detector for detecting an output signal from the frequency converter, the output from the detection wave unit The peak hold circuit that holds the maximum pressure value as the reference value and outputs the reference voltage based on the reference value is compared with the output voltage from the detector and the reference voltage from the peak hold circuit. Is added to the voltage corresponding to the coarse control voltage and the fine control voltage is output, and the fine control voltage value output from the comparator is held and the fine control voltage based on the value is output. And a third control circuit that switches between inputting a fine control voltage from the comparator, inputting a fine control voltage from the hold circuit, or not inputting both as the control voltage of the voltage control filter. comprising a switch, a first specific period until after the tuning operation using a white noise is initiated, the maximum value of the output voltage from the detector is held in the peak hold circuit as a reference value, the The second switch is switched to input the white noise generated by the signal generator, and the second switch is switched to input the coarse control voltage from the D / A converter as the control voltage of the voltage control filter. , a third switch, since the fine adjustment control voltage and the tuning circuit radio switching et al are not to enter both the fine adjustment control voltage from the hold circuit from the comparator, a coarse control voltage, which is the default A precise control voltage adjusted accurately according to individual differences can be generated and input to the voltage control filter, eliminating the need to write individual control voltage values according to individual differences in the filter to the storage unit. In addition to improving productivity, even if there is environmental change or secular change, it can generate the optimal precision control voltage at that time and maintain good characteristics, and detector output Based on these characteristics, there is an effect that a reference voltage for optimally operating the voltage control filter can be generated.

Further, according to the present invention, after the first specific period, in the comparator, the second specific period until the differential voltage between the output voltage from the detector and the reference voltage from the peak hold circuit is stabilized, The first switch is switched to input the white noise generated by the signal generator to the voltage control filter as an input signal, and the second switch controls the coarse control voltage from the D / A converter. is switched so as not to input to the filter, the third switch, since the above-mentioned tuning circuit switched et al is to enter the fine adjustment control voltage from the control voltage and the specific較器of said voltage controlled filter, the default crude There is an effect that a fine control voltage can be generated by adjusting the control voltage according to the individual difference of the voltage control filter.

According to the present invention , the first switch inputs the radio signal from the input terminal as an input signal to the voltage control filter during a period in which the radio signal is input and operated after the second specific period. The second switch is switched so as not to input the coarse control voltage from the D / A converter to the voltage control filter, and the third switch is used as the control voltage of the voltage control filter from the hold circuit. since the above tuning circuit switched et al is to enter Seicho control voltage, during operation, by operating to input fine adjustment control voltage from the hold circuit to the voltage controlled filter, be passed through the desired frequency There is an effect that can be done.

1 is a schematic circuit diagram of a tuning circuit according to an embodiment of the present invention. It is a schematic circuit diagram which shows the state at the time of the reference value acquisition in this tuning circuit. It is a schematic circuit diagram which shows the state at the time of the fine control voltage generation in this tuning circuit. It is a schematic circuit diagram which shows the state at the time of operation | movement in this tuning circuit. It is a schematic circuit diagram of the conventional tuning circuit.

Embodiments of the present invention will be described with reference to the drawings.
[Outline of the embodiment]
A radio tuning circuit according to an embodiment of the present invention includes a ROM in which a coarse control voltage value is written. At the time of tuning, a coarse control voltage is first applied to a VCF, and a signal is used instead of an input signal. The white noise from the generator is input, the output signal is down-converted and detected by the detector, the peak voltage of the detected signal is detected and held by the peak hold circuit, and then the coarse control voltage is set. As a disconnect, the comparator inputs the detection signal from the detector and the peak voltage from the peak hold circuit, adds the difference voltage to a voltage equivalent to the coarse control voltage, and outputs it as a fine control voltage. The fine control voltage is input to the VCF and held in the hold circuit. During operation, an input signal is input to the VCF instead of white noise, and the fine control voltage from the hold circuit is used as the control voltage. By adjusting the default coarse adjustment control voltage so as to absorb the variation of components, the optimum fine control voltage can be generated for each tuning circuit, and the control voltage value can be set for each unit. A writing operation is not required, and an optimum control voltage can be always applied to the VCF by appropriately performing a tuning operation in accordance with the temperature and aging of the use environment.

[Tuning Circuit According to Embodiment: FIG. 1]
A radio tuning circuit according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic circuit diagram of a tuning circuit according to an embodiment of the present invention.
As shown in FIG. 1, a tuning circuit (present tuning circuit) according to an embodiment of the present invention includes an input terminal 11, an output terminal 12, a voltage controlled frequency variable bandpass filter (VCF) 13, a ROM 14, D / A converter 15, signal generator 16, local oscillator 17, mixer 18, IF (Intermediate Frequency) filter 19, detector 20, peak hold circuit 21, comparator 22, and hold circuit 23, a control voltage input terminal 24, a fine control voltage input terminal 25, and switches (SW) 1, SW2, SW3, SW4, and SW5.

The first switch described in the claims corresponds to SW1, the second switch corresponds to SW2, and the third switch combines the functions of SW3 to SW5.
Further, the frequency converter described in the claims is a combination of the functions of the local oscillator 17, the mixer 18, and the IF filter 19.

Each part of the tuning circuit will be described.
The input terminal 11 inputs a radio signal.
The output terminal 12 outputs the intermediate frequency signal down-converted through the VCF 13. If a signal equivalent to the output terminal of the conventional tuning circuit shown in FIG. 4 is to be obtained, a frequency converter (up-converter) for converting to a radio frequency signal may be provided at the output stage of the output terminal 12. Good.
The VCF 13 limits the band of the input signal according to the control voltage and allows a radio signal of a specific frequency to pass as in the conventional case.

The signal generator 16 generates white noise in the input frequency band. White noise is noise having a uniform frequency distribution characteristic in the reception frequency range of the wireless receiver.
SW1 switches the input signal to the VCF 13 to either an input signal from the input terminal 1 or white noise from the signal generator 16.

  The ROM 14 stores voltage data corresponding to the frequency at a specific address, and outputs voltage data corresponding to the set address. A plurality of sets of addresses (frequency) and corresponding voltage data may be stored, and voltage data corresponding to addresses set from the outside may be output.

As a feature of the tuning circuit, the stored voltage data is a default value (coarse control voltage data), and a different value is not written depending on the characteristics of each device. That is, in this tuning circuit, writing of individual control voltage values to the ROM 14 is not performed.
As described above, by using the common ROM 14, the writing operation is unnecessary and the productivity can be improved.

The D / A converter 15 D / A converts the coarse control voltage data from the ROM 14 to generate and output a coarse control voltage as an analog voltage.
SW2 switches whether or not to input the coarse adjustment control voltage from the D / A converter 15 to the control voltage input terminal 24 of the VCF 13, that is, input / disconnection (non-input) of the coarse adjustment control voltage.
The control voltage input terminal 24 is a terminal for inputting a control voltage for the VCF 13.

The local oscillator 17 generates a local frequency signal (LO signal) for converting the high frequency signal output from the VCF 13 into a desired intermediate frequency.
The mixer 18 multiplies the high frequency signal that has passed through the VCF 13 and the local frequency signal from the local oscillator 17 to generate an intermediate frequency (IF) signal.
The IF filter 19 limits the band of the IF signal output from the mixer and removes unnecessary frequency components.

The detector 20, the peak hold circuit 21, the comparator 22, and the hold circuit 23 are portions that generate a fine control voltage, and are characteristic portions of the present tuning circuit.
The detector 20 detects the branched IF signal output from the IF filter 19 and outputs a voltage corresponding to the detection level.
The peak hold circuit 21 receives an output signal (detection signal) from the detector 20, obtains a voltage value, and holds the maximum value of the voltage value in a certain period as a reference value.
The peak hold circuit 21 is provided with an A / D converter at the input portion and a D / A converter at the output portion, and performs digital processing inside the circuit to obtain a reference value. A conversion is performed and a reference voltage is output.

  The comparator 22 receives the detection signal from the detector 20 and the reference voltage from the peak hold circuit 21 and compares them to obtain a differential voltage. Then, a voltage (fine control voltage) obtained by adding the differential voltage to a voltage equivalent to the coarse control voltage output from the D / A converter 15 is output.

  The hold circuit 23 holds the value of the fine control voltage output from the comparator 22. The hold circuit 23 includes an A / D converter at the input stage and a D / A converter at the output stage, as with the peak hold circuit 21.

The fine control voltage output terminal 25 is a terminal that outputs a fine control voltage from the comparator 22 or the hold circuit 23.
SW3 switches whether the output of the fine control voltage output terminal 25 is connected to the control voltage input terminal 24 of the VCF 13, that is, the input / disconnection of the fine control voltage to the VCF 13.
SW4 switches input / disconnection of the fine control voltage from the comparator 22 to the fine control voltage output terminal 25.
SW5 switches input / disconnection of the fine control voltage from the hold circuit 23 to the fine control voltage output terminal 25.

In this tuning circuit, three switches SW3 to SW5 are used in order to switch the fine control voltage input / disconnection to the control voltage input terminal 24, but one switch is used instead. May be.
In this case, the change-over switch inputs the fine control voltage from the comparator 22, the fine control voltage from the hold circuit 23, or none of the three as the control voltage of the VCF 13. Switch state.
In other words, the changeover switch switches the state in which the control voltage input terminal 24 of the VCF 13 is connected to the output of the comparator 22, connected to the output of the hold circuit 23, or not connected to both.
The third switch in the claims corresponds to such a change-over switch.

[Operation in this tuning circuit]
The operation of the tuning circuit will be described with reference to FIGS.
In this tuning circuit, three types of operations are performed: reference value acquisition, fine control voltage generation, and operation. In each operation, the open / close state of the switch is different. The reference value acquisition and fine control voltage generation operations are collectively referred to as a tuning operation.
[When obtaining reference values: Fig. 2]
First, the operation at the time of obtaining the reference value will be described with reference to FIG. FIG. 2 is a schematic circuit diagram showing a state when the reference value is acquired in the tuning circuit.
As shown in FIG. 2, when the reference value is acquired, SW1 is switched to the signal generator 16, SW2 is connected, and SW3 is disconnected.

When the tuning operation is started, SW1 is switched to the signal generator 16 side, white noise including a desired frequency band is input to VCF 13, SW2 is connected, and a D / A converter is used as a control voltage. The coarse control voltage from 15 is input.
The VCF 13 band-limits white noise based on the coarse control voltage, and allows a radio signal in a frequency band near the set frequency to pass.

The radio signal that has passed through the VCF 13 is multiplied by the local signal from the local oscillator 17 by the mixer 18 and converted into an intermediate frequency signal.
Here, the frequency of the local signal is a frequency at which a specific intermediate frequency signal can be obtained by multiplying by the set frequency to be passed by the VCF 13.
Unnecessary waves are removed from the intermediate frequency signal by the IF filter 19 to become a specific intermediate frequency signal.

The output of the IF filter 19 is branched and input to the detector 20 where it is detected.
The output of the detector 20 is branched, one is input to the comparator 22 and the other is input to the peak hold circuit 21.
The peak hold circuit 21 detects the voltage value input from the detector 20 and holds the maximum value. If the input voltage value is larger than the maximum value so far, the maximum value is updated with the input voltage value. And hold.
By continuing this state for a specific period, the peak hold circuit 21 holds the maximum value of the detection output within the period as a reference value.
A reference voltage is output from the peak hold circuit 21 based on the reference value.

Here, the voltage level of the output signal (IF signal) of the IF filter 19 becomes maximum when the pass characteristic of the VCF 13 matches the set frequency.
That is, when the pass characteristic of the VCF 13 is optimal, the shoulder characteristic of the IF signal is the best (wide band and large voltage level), and the output level of the detector 20 is maximum (peak). is there.
This tuning circuit uses this fact to obtain an optimum control voltage that allows the VCF 13 to pass a desired frequency signal.
In this way, the reference value acquisition operation in the tuning circuit is performed.

[When fine control voltage is generated: Fig. 3]
Next, the operation when generating the fine control voltage will be described with reference to FIG. FIG. 3 is a schematic circuit diagram showing a state when the fine control voltage is generated in the tuning circuit.
After the reference value is held in the peak hold circuit 21, as shown in FIG. 3, SW1 is switched to the signal generator 16, SW2 is disconnected, SW3 is connected, SW4 is connected, and SW5 is disconnected. It becomes the operation of fine control voltage generation.

When the fine control voltage is generated, the coarse control voltage from the D / A converter 15 is disconnected.
Then, the output from the detector 20 and the output (reference voltage) from the peak hold circuit 21 are input to the comparator 22, and the difference voltage between them is obtained in the comparator 22.
The differential voltage is a differential voltage between the detection output in the best state and the detection output at each time point.

Then, a fine control voltage obtained by adding the differential voltage to a voltage equivalent to the coarse control voltage from the D / A converter 15 is output from the comparator 22 and applied as a control voltage to the VCF 13 via SW4 and SW3. The
At the same time, the value of the fine control voltage from the comparator 22 is held in the hold circuit 23.

By operating for a specific period in the state of FIG. 3, the differential voltage is stabilized, and the optimum control voltage to the VCF 13 of the tuning circuit is held in the hold circuit 23 as the value of the fine control voltage.
The fine control voltage is a control voltage adjusted so as to compensate for variations in individual components of the tuning circuit with respect to the coarse control voltage.
In this way, the operation at the time of fine control voltage generation in the tuning circuit is performed.

[Operation: Fig. 4]
Next, operations during operation will be described with reference to FIG. FIG. 4 is a schematic circuit diagram showing a state of the tuning circuit during operation.
As shown in FIG. 4, during operation, SW1 is switched to the input terminal 11 side, SW2 is disconnected, SW3 is connected, SW4 is disconnected, and SW5 is connected.
Then, a fine control voltage based on the fine control voltage value stored in the hold circuit 24 is applied to the VCF 13 from the control voltage input terminal 24 via SW5 and SW3, and the VCF 13 is based on the fine control voltage. The input signal from the input terminal is band-limited, and a desired set frequency is passed with high accuracy.

  As described above, this tuning circuit eliminates the need to individually write the control voltage value to each circuit, can be autonomously tuned with high accuracy, and can improve productivity.

  In addition, by storing a plurality of sets of frequencies and corresponding coarse adjustment control voltage data in the ROM 14 in advance, when the passing frequency is changed, an address corresponding to the frequency to be used is set from the outside and tuned. If the operation is performed, the VCF 13 can be tuned to the changed frequency, and the frequency used by the radio can be easily changed.

  Furthermore, in order to cope with temperature characteristics and aging changes, for example, when the installation environment changes or by performing a tuned operation at regular intervals after the start of operation, the temperature characteristics and aging changes are included. It is possible to generate an optimum fine control voltage according to the state and obtain stable characteristics.

Further, as another configuration, an adder is provided in place of the control voltage input terminal 24, and the output from the fine control voltage output terminal 25 is added to the coarse control voltage from the D / A converter 15 by the adder. Then, it may be output to the VCF 13. In this case, the comparator 22 outputs a differential voltage between the reference voltage from the peak hold circuit 21 and the output from the detector 20.
The output from the adder is a voltage obtained by adding or subtracting the differential voltage to the coarse control voltage according to the sign of the differential voltage.
Further, in this case, SW2 is not necessary, and the comparator 22 can be simply output a difference.

[Effect of the embodiment]
According to the tuning circuit according to the embodiment of the present invention, when obtaining the reference value, white noise is input to the VCF 13 and a coarse control voltage based on the coarse control voltage value stored in the ROM 14 is input, and the output of the VCF 13 is output. Is converted into IF frequency, detected by the detector 20, the peak voltage is held by the peak hold circuit 22, and when the fine control voltage is generated, the coarse control voltage is cut off, and the detector is detected by the comparator 22. The difference between the output of 20 and the reference voltage from the peak hold circuit 21 is obtained, and a fine control voltage obtained by adding the difference to a voltage equivalent to the coarse control voltage is generated and output. The control voltage is held, and during operation, the input signal is input with white noise cut off, and the fine control voltage from the hold circuit 23 is used as the control voltage of the VCF 13. Therefore, while using the ROM 14 in which the common coarse voltage value is written, the control voltage that absorbs the variation of the components of the VCF 13 and obtains the optimum filter characteristic for each VCF 13 is used as the fine control voltage. Therefore, there is an effect that productivity can be improved by eliminating the need to individually write the control voltage to the ROM.

  When changing the frequency, the VCF 13 can be tuned to the changed frequency by designating the address corresponding to the changed frequency to the ROM 14 and performing the tuning operation, so that the frequency change can be easily handled. There is an effect that can be done.

  In addition, even after the start of operation, if there is an environmental change or secular change, by performing the tuning operation again, it is possible to generate an optimal fine control voltage in the state at that time, and it has good characteristics There is an effect that can be maintained.

  INDUSTRIAL APPLICABILITY The present invention is suitable for a radio tuning circuit that can improve productivity and maintain good characteristics.

  11, 31 ... input terminal, 12, 32 ... output terminal, 13, 33 ... voltage controlled frequency variable bandpass filter (VCF), 14, 34 ... ROM, 15, 35 ... D / A converter, 16 ... signal generator, 17 ... local oscillator, 18 ... mixer, 19 ... IF filter, 20 ... detector, 21 ... peak hold circuit, 22. ..Comparator, 23 ... Hold circuit, 24 ... Control voltage input terminal, 25 ... Precision control voltage output terminal

Claims (3)

A tuning circuit for a radio,
An input terminal for inputting a radio signal;
A signal generator that generates white noise;
A voltage control filter that passes and outputs a specific frequency according to the control voltage for the input signal;
A first switch for switching to input either a radio signal input to the input terminal or white noise generated by the signal generator as an input signal of the voltage control filter;
A storage unit for storing a coarse control voltage value corresponding to the specific frequency;
A D / A converter that D / A converts the coarse control voltage value and outputs a coarse control voltage;
A second switch for switching whether to input the coarse control voltage as the control voltage to the voltage control filter;
A frequency converter that converts an output signal from the voltage control filter into an intermediate frequency;
A detector for detecting an output signal from the frequency converter;
Holding the maximum value of the output voltage from the previous SL detector as a reference value, a peak hold circuit for outputting a reference voltage based on the reference value,
A comparator that inputs and compares an output voltage from the detector and a reference voltage from the peak hold circuit, adds a differential voltage to a voltage corresponding to the coarse control voltage, and outputs a fine control voltage; ,
A hold circuit for holding a value of the fine control voltage output from the comparator and outputting a fine control voltage based on the value;
A third switch for switching whether to input a fine control voltage from the comparator, a fine control voltage from the hold circuit, or not to input both as the control voltage of the voltage control filter; With
During the first specific period from when the tuning operation using white noise is started to when the maximum value of the output voltage from the detector is held as the reference value in the peak hold circuit, the first switch The white switch generated by the signal generator is switched to input, and the second switch is switched to input the coarse control voltage from the D / A converter as the control voltage of the voltage control filter. is, the third switch, fine adjustment control voltage and the tuning circuit radios, characterized in that it is switched so as not to enter both the fine adjustment control voltage from the hold circuits from the comparator. After the first specific period, in the comparator, the second specific period until the differential voltage between the output voltage from the detector and the reference voltage from the peak hold circuit is stabilized,
The first switch is switched to input the white noise generated by the signal generator to the voltage control filter as an input signal, and the second switch controls the coarse control voltage from the D / A converter. It is switched so as not to input to the filter, the third switch is tuned according to claim 1, wherein the switching et Reruko to enter the fine adjustment control voltage from the comparator as a control voltage of said voltage control filter circuit. After the second specific period, the period of operation by inputting a radio signal is
The first switch is switched to input a radio signal from the input terminal as an input signal to the voltage control filter, and the second switch inputs the coarse control voltage from the D / A converter to the voltage control filter. switched lest, third switch, a tuning circuit according to claim 2, wherein the switching et Reruko to enter the fine adjustment control voltage from the hold circuit as a control voltage of said voltage controlled filter.

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