JP2013102275A - Filter circuit, and method and program for controlling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter circuit in which a center frequency of a band-pass filter can be easily and optionally changed, and a method and program for controlling the same.SOLUTION: A filter circuit 1 includes a band-pass filter 2 which has a changeable center frequency, and outputs a first output signal by filtering the input signal; an adjustment signal generation unit 3 for generating an adjustment signal containing a first signal having a frequency of f1 and a second signal having a frequency of f2; a band-pass filter 4 outputting a second output signal having the changeable center frequency by filtering the adjustment signal; and a control signal generation circuit 5 which detects an intensity of the second output signal and generates a control signal for controlling the center frequency of the band-pass filter 2 and band-pass filter 4.

Description

  The present invention relates to a filter circuit, a control method thereof, and a control program thereof.

  A frequency variable filter whose frequency passband is controllable is an industrially important technology and is used in many applications. For example, as in the case of cognitive radio, attempts to increase bandwidth utilization efficiency by adaptively changing radio transmission / reception parameters including frequency are currently attracting attention. For this reason, in a wireless transceiver, it is necessary to easily realize a filter that can be controlled to change the frequency.

  FIG. 7 shows a configuration of a general filter circuit. The filter circuit 200 includes a frequency variable filter 201, a control circuit 202, and a setting unit 203. The frequency variable filter 201 is a bandpass filter whose center frequency is variable. The control circuit 202 outputs a control signal for changing the center frequency to the frequency variable filter 201. The setting unit 203 includes a CPU (Central Processing Unit) and a memory. The setting unit 203 reads the initial setting value of the center frequency and the temperature correction value, calculates the setting value of the center frequency, and outputs the setting value to the control circuit 202. Thereby, the setting unit 203 sets the control circuit 202 so that the frequency variable filter 201 sets the center frequency to the frequency. The control circuit 202 outputs a control signal for setting the center frequency to the frequency variable filter 201. Thereby, the frequency variable filter 201 changes the center frequency. The control voltage in the control signal of the frequency variable filter 201 needs to be determined in advance by inspection or the like.

  In the filter circuit 200 shown in FIG. 7, since it is considered that the control voltage of the frequency variable filter 201 has a variation, an inspection is performed for each unit, or a design is made with a margin in consideration of the variation. There is a need. Furthermore, in setting the center frequency, it is necessary to consider parameters such as temperature characteristics and changes with time.

  A specific example of a bandpass filter having a variable center frequency is as follows, for example. In Cited Document 1, the phase detector detects the phase difference between the signal waveform that has passed through the bandpass filter and the signal waveform that has not passed through, thereby determining the deviation of the center frequency of the bandpass filter. The technology of a filter control device for controlling the above is described.

  Cited Document 2 describes a broadcast signal receiving apparatus including two band pass filters, an RF filter circuit and an IF filter circuit to which a signal of the circuit is input. The control device of the broadcast signal receiving apparatus is configured so that the detection output level of the output signal of the RF filter circuit is not more than a predetermined value within a range where the detection output level of the output signal of the IF filter circuit is not less than the predetermined level. Sets the pass frequency of the filter circuit. Thereby, the broadcast signal receiving apparatus can sufficiently attenuate the signal (interference signal) of the adjacent channel while extracting the signal (desired signal) of the reception channel.

JP 2006-005485 A JP 2010-258733 A

  The filter control apparatus according to the cited document 1 controls the center frequency of the bandpass filter using the phase difference generated by the passage of the bandpass filter. However, in general, when a high-frequency signal is filtered, a phase delay is caused by the routing of the wiring, so it is necessary to provide a phase shifter. Since the phase of the signal that passes through the bandpass filter and the phase of the signal that does not pass are generally considered to vary, it is considered that calibration is required for phase detection. That is, calibration processing is required to control the communication frequency of the bandpass filter to a desired value.

  The broadcast signal receiving apparatus according to the cited document 2 is adjusted so that the interference signal is attenuated by the band-pass filter according to the frequency of the desired signal and the interference signal. For this reason, this broadcast signal receiving apparatus does not arbitrarily change the center frequency of the bandpass filter.

  The present invention has been made to solve such problems, and an object thereof is to provide a filter circuit that easily and arbitrarily changes the center frequency of a bandpass filter, a control method thereof, and a control program thereof. To do.

  The filter circuit according to the present invention includes a first band-pass filter having a changeable center frequency, filtering an input signal and outputting a first output signal, a first signal having a frequency f1, and a frequency f2. An adjustment signal generator for generating an adjustment signal including a second signal; a second bandpass filter having a changeable center frequency and filtering the adjustment signal to output a second output signal; A control signal generation circuit that detects the intensity of the second output signal and generates a control signal for controlling a center frequency of the first bandpass filter and the second bandpass filter according to the detection result; Is provided.

  The method for controlling a filter circuit according to the present invention includes a step of filtering an input signal by a first bandpass filter having a changeable center frequency to output a first output signal, and a first signal having a frequency f1 And generating a regulated signal including a second signal having a frequency f2, and filtering the input signal with a second bandpass filter having a changeable center frequency to output a second output signal; Detecting the intensity of the second output signal, and generating a control signal for controlling a center frequency of the first bandpass filter and the second bandpass filter according to the detection result. .

  A control program for a filter circuit according to the present invention includes a step of filtering an input signal by a first bandpass filter having a changeable center frequency to output a first output signal, and a first signal having a frequency f1 And generating a regulated signal including a second signal having a frequency f2, and filtering the input signal with a second bandpass filter having a changeable center frequency to output a second output signal; Detecting a strength of the second output signal and generating a control signal for controlling a center frequency of the first bandpass filter and the second bandpass filter according to the detection result. Let the circuit run.

  According to the present invention, it is possible to provide a filter circuit that easily and arbitrarily changes the center frequency of a bandpass filter, a control method thereof, and a control program thereof.

1 is a block diagram of a filter circuit according to a first embodiment. FIG. 6 is a block diagram of a filter circuit according to a second embodiment. 6 is a graph showing a spectrum of an RF signal according to the second embodiment. 10 is a graph showing a spectrum of an adjustment signal according to the second embodiment. 6 is a graph showing a detection output level of a detection signal Vdet according to the second exemplary embodiment; 6 is a graph showing detection output levels of detection signals Vdet1 and Vdet2 according to the second embodiment; It is a block diagram of the filter circuit concerning related technology.

Embodiment 1
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a filter circuit according to the first embodiment. The filter circuit 1 according to the first embodiment includes a bandpass filter 2, an adjustment signal generator 3, a bandpass filter 4, and a control signal generation circuit 5.

  In the filter circuit 1, the adjustment signal generator 3 generates an adjustment signal including the first signal having the frequency f1 and the second signal having the frequency f2, and the band-pass filter 4 filters the adjustment signal to generate a second signal. The output signal is output. The control signal generation circuit 5 controls the center frequencies of the bandpass filters 2 and 4 according to the detection result of the intensity (output voltage) of the second output signal. Thereby, the control signal generation circuit 5 can change the center frequency of the band pass filter 2 to an arbitrary frequency.

  Hereinafter, each part of the filter circuit 1 will be described. The band pass filter 2 filters the input signal and outputs a first output signal. The bandpass filter 2 has a pass band centered on a specific frequency f0, and the specific frequency f0 is hereinafter referred to as a center frequency. The bandpass filter 2 is a filter circuit that can change the center frequency f0.

  The adjustment signal generator 3 outputs an adjustment signal to the bandpass filters 2 and 4. This adjustment signal is a signal for adjusting the value of the center frequency f0 of the bandpass filters 2 and 4, and includes a first signal having the frequency f1 and a second signal having the frequency f2. The adjustment signal generator 3 may output the first signal and the second signal simultaneously as the adjustment signal, or may switch and output the first signal and the second signal as the adjustment signal. .

  The bandpass filter 4 filters the adjustment signal output from the adjustment signal generator 3 and outputs a second output signal. The bandpass filter 4 can change the center frequency f0 and has the same pass characteristics as the bandpass filter 2. That is, when signals having the same frequency and the same intensity are input to the bandpass filter 2 and the bandpass filter 4, the bandpass filters 2 and 4 output the signals with substantially the same intensity. Note that “substantially the same” means that the intensity of the signal can change only in an error or a numerical value within an allowable range.

  The control signal generation circuit 5 detects the intensity of the second output signal output from the bandpass filter 4. That is, the control signal generation circuit 5 detects the strengths of the first signal and the second signal filtered by the band pass filter 4. The control signal generation circuit 5 generates a control signal for controlling the center frequency f0 of the bandpass filters 2 and 4 in accordance with the detected first signal and second signal intensity. The bandpass filters 2 and 4 change the center frequency f0 according to the control signal.

  The control signal generation circuit 5 includes, for example, a detection circuit that detects a voltage, a comparison circuit that compares voltages, and the like.

  Hereinafter, the processing of the filter circuit 1 will be described with a specific example.

  The adjustment signal generator 3 outputs an adjustment signal including a first signal having the same frequency f1 and a second signal having the frequency f2 having the same intensity (here, f1 <f2). The desired center frequency f3 of the band-pass filter 2 is the intensity of the first signal and the second signal filtered by the band-pass filter 2 when the center frequency f0 of the band-pass filter 2 is f0 = f3. Are frequencies that are substantially the same. The frequencies f1, f2, and f3 have a magnitude relationship of f1 <f3 <f2.

  The control signal generation circuit 5 detects and compares the intensities of the first signal and the second signal filtered by the band pass filter 4. Then, a control signal is generated so that the center frequency f0 of the bandpass filters 2 and 4 becomes the desired center frequency f3. For example, when the center frequency f0 of the bandpass filter 2 is f0 = f2 and the ratio of the intensity of the filtered first signal and second signal is 1:10, the control signal generation circuit 5 A control signal for lowering the center frequency f0 is output to the bandpass filters 2 and 4. When the filtered first signal and second signal have substantially the same intensity, the control signal generation circuit 5 stops generating the control signal that changes the center frequency f0. As a result, the control signal generation circuit 5 sets the center frequency f0 of the bandpass filters 2 and 4 to the desired center frequency f3.

  When the values of the frequency f1 of the first signal and the frequency f2 of the second signal output from the adjustment signal generator 3 are changed from this state, the intensity of the filtered first signal and the intensity of the second signal Will change. In response to this change in intensity, the control signal generation circuit 5 changes the center frequency f0 of the bandpass filters 2 and 4 until the intensity of the filtered first signal and that of the second signal are substantially the same. A control signal to be changed is generated. The bandpass filters 2 and 4 change the center frequency f0 according to the control signal.

  By changing the frequency f1 of the first signal and the frequency f2 of the second signal by the above processing, the filter circuit 1 automatically sets the center frequency f0 of the bandpass filter 2 to the desired frequency f3. Can do.

  As described above, since the filter control device according to the cited document 1 changes the center frequency by detecting the phase, calibration is necessary for detection, and the processing of the filter control device is considered to increase. The control device according to the cited document 2 cannot arbitrarily change the center frequency.

  The control signal generation circuit 5 of the present embodiment detects the intensity of the second output signal output from the band pass filter 4. Thereby, since calibration for detection is unnecessary, the center frequency of the bandpass filter 2 can be easily changed. Furthermore, the center frequency of the band pass filter 2 can be arbitrarily changed by changing the frequency f1 of the first signal and the frequency f2 of the second signal output from the adjustment signal generator.

  The filter circuit 1 can be used for a wireless transmitter, receiver, and the like.

  In the specific example described above, the first signal and the second signal in the adjustment signal have the same strength, but may be signals having different strengths.

  In the above specific example, the center frequencies of the bandpass filters 2 and 4 are the same frequency f0, but may be different frequencies. For example, the center frequency of the bandpass filter 2 in the initial state is f01, the center frequency of the bandpass filter 4 is f02, and the relationship between f01 and f02 is f02 = f01 + Δf (Δf is f01 and f02). It is a value that indicates the difference between. The band-pass filters 2 and 4 output the signals with substantially the same intensity when the same intensity signals having the same frequency shifted in the same direction in the upper and lower directions from the respective center frequencies are input. To do. In other words, the band-pass filters 2 and 4 have substantially the same graph shape with the same pass characteristics although the center frequencies are different.

  In this case, in order to adjust the center frequency of the bandpass filter 2 to the desired frequency f03, the frequency f1 of the first signal and the frequency f2 of the second signal in the adjustment signal are changed, and the bandpass filter The center frequency of 4 may be changed to f03 + Δf. In this way, the filter circuit 1 can arbitrarily change the center frequency of the bandpass filter 2.

Embodiment 2
Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 2 is a block diagram of a filter circuit according to the second embodiment. The filter circuit 100 is roughly divided into a modulator 10 (second modulator), a local oscillator 20, a bandpass filter 30, an intermediate signal generation unit 40, a modulator 50 (first modulator), and a bandpass filter 60. A control signal generation circuit 70 and a pulse signal source 90.

  The filter circuit 100 is a filter circuit used in a wireless transmitter, and modulates transmission baseband signals I and Q (hereinafter referred to as signals I and Q) into RF signals (high-frequency signals) and outputs them.

  A local oscillator 20 that outputs a local signal L is connected to the modulator 10. Based on the local signal L, the modulator 10 modulates the signals I and Q into an RF signal. Here, the signal I is an in-phase component signal, the signal Q is a quadrature component signal, the former is a sin wave, and the latter is a cosine wave.

  The modulator 10 includes mixers 11 and 12, a phase shifter 13, and a sigma adder 14. The mixer 11 receives the signal I and a signal obtained by adding a phase of 90 degrees to the local signal L by the phase shifter 13, and the mixer 11 outputs a frequency-converted signal based on these two signals. To do. The local signal L is a modulation signal output from the local oscillator 20 and has a frequency of fL. The mixer 12 receives the signal Q and the local signal L, and the mixer 12 outputs a frequency-converted signal based on these two signals.

  The phase shifter 13 adds a 90-degree phase to the local signal L and outputs it to the mixer 11. The sigma adder 14 adds the signals output from the mixer 11 and the mixer 12 and outputs the added signal to the bandpass filter 30. As described above, the modulator 10 outputs an RF signal to the bandpass filter 30.

  FIG. 3 is a graph showing the spectrum of the RF signal. In this RF signal diagram, the horizontal axis represents the frequency f, and the vertical axis represents the spectral intensity. The RF signal has a frequency band in which the spectrum intensity is high with the frequency fL as the center.

The local oscillator 20 outputs a local signal L having a frequency fL, which is a modulation signal, to the modulator 10 and the modulator 50. The waveform of the local signal L is a _{sinω 2 t (ω 2 = fL} × 2π).

  The band pass filter 30 is an RF filter that filters the RF signal output from the modulator 10 and outputs a transmission RF signal. When the center frequency f0 of the bandpass filter 30 is f0 = fL, the transmission RF signal has a high spectral intensity only at the frequency fL and the vicinity thereof, and signals at other frequencies are attenuated. In this way, the bandpass filter 30 suppresses signals outside the band in the RF signal and transmits and transmits them.

  The bandpass filter 30 changes the passband by changing the center frequency f0 according to the control voltage of the control signal of the amplifier circuit 72. Specifically, the center frequency f0 changes as the capacitance of the capacitor in the bandpass filter 30 changes according to the change in the control voltage of the control signal. For example, the center frequency f0 of the band pass filter 30 can be increased as the control voltage of the control signal increases. Note that the pass characteristics of the bandpass filter 30 are symmetrical with respect to the center frequency f0.

The intermediate signal generation unit 40 outputs two IF signals (intermediate frequency signals) R and S having the frequency fIF to the modulator 50. The intermediate signal generation unit 40 functions as a switch that alternately switches between a sine wave waveform and a cosine wave waveform according to the pulse signal output from the pulse signal source 90 and outputs them as IF signals R and S. When the waveform of the IF signal R is sin ω ₁ t (ω ₁ = fIF × 2π), the waveform of the IF signal S is cos ω ₁ t. Conversely, when the waveform of the IF signal R is cos .omega ₁ t, the waveform of the IF signal S is sin .omega ₁ t.

The intermediate signal generation unit 40 includes a CW signal source (continuous wave signal source) 41, a resistor 42, RF switches (high frequency switches) 43 and 44, and a 90-degree hybrid circuit 45. The CW signal source 41 outputs a CW signal having a frequency of fIF and a waveform of sin ω ₁ t to one end of the input terminals of the RF switches 43 and 44. The resistor 42 has one end grounded and the other end connected to the other ends of the input terminals of the RF switches 43 and 44.

  The RF switches 43 and 44 have one input terminal connected to the CW signal source 41 and the other end connected to the resistor 42. The output terminal of the RF switch 43 is connected to the IN terminal of the 90-degree hybrid circuit 45. The output terminal of the RF switch 44 is connected to the ISO terminal of the 90-degree hybrid circuit 45.

  The RF switch 43 switches input terminals to be connected at predetermined time intervals based on the pulse signal output from the pulse signal source 90. As a result, the RF switch 43 switches the input signal at a predetermined interval and outputs the input signal to the IN terminal of the 90-degree hybrid circuit 45. The RF switch 44 switches the input signal at a timing opposite to that of the RF switch 43 by the pulse signal source 90 and outputs the input signal to the ISO terminal of the 90-degree hybrid circuit 45.

  When a signal is input to the IN terminal, the 90-degree hybrid circuit 45 outputs the signal from the 0 ° terminal as it is (without changing the phase) as the IF signal R. From the 90 ° terminal, the phase of the signal is changed by 90 degrees and output as an IF signal S.

For example, when the output terminal of the RF switch 43 and the CW signal source 41 are connected, the CW signal having the waveform sin ω ₁ t is input to the IN terminal. At this time, since the grounded resistor 42 is connected to the output terminal of the RF switch 44, no signal is input to the ISO terminal. Here 90-degree hybrid circuit 45, the IF signal R wave cos .omega ₁ t from 90 ° terminal, and outputs the IF signal S of the waveform sin .omega ₁ t from 0 ° pin.

  When a signal is input to the ISO terminal, the 90-degree hybrid circuit 45 changes the phase of the signal from the 0 ° terminal by 90 degrees and outputs it as an IF signal R. From the 90 ° terminal, the signal is output as it is (without changing the phase) as the IF signal S.

For example, when the output terminal of the RF switch 43 and the grounded resistor 42 are connected, no signal is input to the IN terminal. At this time, since the CW signal source 41 is connected to the output terminal of the RF switch 44, the CW signal having the waveform sin ω ₁ t is input to the ISO terminal. Here 90-degree hybrid circuit 45, the IF signal R of the waveform sin .omega ₁ t from 90 ° terminal, and outputs the IF signal S waveform cos .omega ₁ t from 0 ° pin.

  The 90-degree hybrid circuit 45 outputs the IF signals R and S in this way.

  A local oscillator 20 common to the modulator 10 is connected to the modulator 50. Based on the local signal L, the modulator 50 modulates the signals R and S into adjustment signals. The intermediate signal generator 40 and the modulator 50 correspond to the adjustment signal generator 3 in the first embodiment.

  The modulator 50 includes mixers 51 and 52, a phase shifter 53, and a sigma adder 54. The mixer 51 receives the signal R and the local signal L, and the mixer 51 outputs a signal obtained by converting the frequency based on the two signals. The mixer 52 receives the signal S and a signal obtained by adding a phase of 90 degrees to the local signal L by the phase shifter 53, and the mixer 52 outputs a frequency-converted signal based on the two signals. . The phase shifter 53 adds a phase of 90 degrees to the local signal L and outputs it to the mixer 52.

  The sigma adder 54 adds the signals output from the mixer 51 and the mixer 52, and outputs the added signal to the bandpass filter 60. The sigma adder 54 outputs, as adjustment signals, a first signal having a frequency f1 (f1 = fL−fIF) and a second signal having a frequency f2 (f2 = fL + fIF) as a pulse signal output from the pulse signal source 90. The output is switched at the same timing as when the is switched.

  FIG. 4 is a graph showing the spectra of the first signal and the second signal. In FIG. 4, the horizontal axis indicates the frequency f, and the vertical axis indicates the spectrum intensity.

  The band pass filter 60 filters the adjustment signal output from the modulator 50 and outputs a detection signal to the control signal generation circuit 70. The bandpass filter 60 can change the center frequency f0 and has the same pass characteristics as the bandpass filter 30. The bandpass filter 60 can change the passband by changing the center frequency f0 according to the control signal of the amplifier circuit 72.

  Here, the frequency fIF of the intermediate signal generated by the intermediate signal generation unit 40 is larger than half the frequency of the pass bandwidth of the bandpass filters 30 and 60. In other words, the pass bandwidth of the bandpass filters 30 and 60 is less than | f2-f1 |. Therefore, both the frequency f1 of the first signal output from the modulator 50 and the frequency f2 of the second signal are not within the passband of the bandpass filter 60. At least one of the first signal and the second signal is attenuated by being filtered by the bandpass filter 60.

  The control signal generation circuit 70 detects the intensity of the detection signal output from the bandpass filter 60, and generates a control signal for controlling the center frequency f0 of the bandpass filters 30 and 60 based on the result. The band pass filters 30 and 60 change the center frequency f0 according to the control signal.

  The control signal generation circuit 70 includes a detection circuit 71, an amplification circuit 72, and a filter unit 80. The detection circuit 71 detects the intensity of the detection signal. In other words, the detection circuit 71 detects the intensity of the first signal having the frequency f1 filtered by the bandpass filter 60 and the intensity of the second signal having the frequency f2. The detection circuit 71 outputs the detection result to the filter unit 80 as a detection signal Vdet.

  FIG. 5 is a graph showing the detection output level of the detection signal Vdet. In this graph, the horizontal axis represents time t, and the vertical axis represents the intensity (voltage) of the detection signal Vdet. In the detection signal Vdet, the detection voltage of the first signal and the detection voltage of the second signal appear alternately at the timing when the pulse of the pulse signal source 90 is switched.

  The detection signal Vdet is input to the filter unit 80. The filter unit 80 separates the detection signal Vdet into the detection voltage of the first signal and the detection voltage of the second signal, averages the values of the detection signals, and outputs them to the amplification circuit 72.

  The filter unit 80 includes switches 81 and 82, resistors 83 and 84, and capacitors 85 and 86. A detection signal Vdet is input to each of the switches 81 and 82. One of the input terminals of the switch 81 is connected to the signal line of the detection signal Vdet, and the other input terminal is grounded. The switch 81 intermittently acquires the detection signal Vdet by switching the input terminal connected at a predetermined time interval based on the pulse signal output from the pulse signal source 90. Thereby, the switch 81 acquires only the detection voltage of the first signal and outputs it as the detection signal Vdet1. Then, the acquired signal is output as a detection signal Vdet1 to a low-pass filter including a resistor 83 and a capacitor 85.

  The switch 82 has the same configuration as the switch 81. The switch 82 intermittently acquires the detection signal Vdet at a timing opposite to that of the switch 81 based on the pulse signal. Thereby, the switch 82 acquires only the detection voltage of the second signal and outputs it as the detection signal Vdet2. Then, the acquired signal is output as a detection signal Vdet2 to a low-pass filter including a resistor 84 and a capacitor 86.

  FIG. 6 is a graph showing detection output levels of the detection signal Vdet1 and the detection signal Vdet2. In this graph, the horizontal axis indicates time t, and the vertical axis indicates the intensity of the detection signals Vdet1 and Vdet2.

  The output terminal of the switch 81 is connected to one end of the resistor 83. The other end of the resistor 83 is connected to the non-inverting input terminal of the amplifier circuit 72. One end of a capacitor 85 is connected to the other end of the resistor 83 in parallel with the amplifier circuit 72. The other end of the capacitor 85 is grounded. In this way, the resistor 83 and the capacitor 85 constitute a low-pass filter.

  One end of the resistor 84 is connected to the inverting input terminal of the amplifier circuit 72. The resistor 84 and the capacitor 86 are connected in the same manner as the resistor 83 and the capacitor 85, and constitute a low-pass filter.

  Here, the frequency of the pulse signal is sufficiently higher than the cutoff frequency of the low-pass filter. Accordingly, the filter unit 80 outputs the average value of the intensity of the detection signal Vdet1 to the non-inverting input terminal of the amplifier circuit 72, and outputs the average value of the intensity of the detection signal Vdet2 to the inverting input terminal of the amplifier circuit 72.

  The amplifier circuit 72 monitors the average value of the detection signal Vdet1 and the average value of the intensity of the detection signal Vdet2, and compares the magnitudes. Then, the control signal is output to the bandpass filters 30 and 60 so that the respective output voltages from the filter unit 80 become the same. Here, the amplifier circuit 72 is configured by an output amplifier.

  The amplifier circuit 72 outputs a control signal to the control terminals of the bandpass filters 30 and 60. The band pass filters 30 and 60 change the center frequency in response to the change in the control voltage of the control signal of the amplifier circuit 72. Thereby, the band pass filters 30 and 60 can change a pass band.

  The pulse signal source 90 outputs a pulse signal having a DUTY ratio of 50% to the RF switches 43 and 44 of the intermediate signal generation unit 40 and to the switches 81 and 82 of the filter unit 80. That is, the switches 43 and 44 and the switches 81 and 82 are switched ON and OFF by a common pulse signal.

  Hereinafter, a process in which the filter circuit 100 sets the center frequency f0 of the bandpass filter 30 to the frequency fL will be described.

  It is assumed that the center frequency f0 of the bandpass filters 30 and 60 is deviated from fL. In this case, since the pass characteristics of the bandpass filters 30 and 60 are substantially symmetrical with respect to the center frequency, the first frequency f1 (f1 = fL−fIF) filtered by the bandpass filter 60 is used. And the intensity of the second signal having the frequency f2 (f2 = fL + fIF) are not substantially the same. Note that whether the intensity of the first signal or the intensity of the second signal is higher differs depending on whether the center frequency f0 is shifted up or down from fL.

  While the intensity of the first signal and the intensity of the second signal filtered by the band pass filter 60 are not the same, the DUTY ratio of the pulse signal is 50%, so the first signal and the second signal are The output time is the same. For this reason, the average value of the intensity of the first signal output from the filter unit 80 is different from the average value of the intensity of the second signal. As described above, the amplifier circuit 72 compares the two average values. In this case, since both are not the same value, the amplifier circuit 72 outputs a control signal for changing the center frequency f0 of the bandpass filters 30 and 60 so that these values are at the same level. .

  With the above processing, the center frequency f0 of the bandpass filter 60 becomes the same as fL. As a result, the center frequency f0 of the bandpass filter 30 that outputs the transmission RF signal is also set to fL. That is, the band pass filter 30 is controlled to have a pass band centered on the frequency fL.

  Assume that the center frequency f0 of the bandpass filters 30 and 60 is the same as fL. In this case, the intensity of the first signal passing through the bandpass filter 60 is substantially the same as the intensity of the second signal.

  Since the time when the first signal and the second signal are output is the same, the average value of the first signal intensity output from the filter unit 80 and the average value of the second signal intensity are substantially the same. The same. Since the intensity values input to the inverting input terminal and the non-inverting input terminal of the amplifier circuit 72 are substantially the same, the amplifier circuit 72 outputs a control signal for controlling the center frequency f0 to the bandpass filters 30 and 60. do not do. As a result, the center frequencies of the bandpass filters 30 and 60 remain unchanged.

  Here, it is assumed that the user increases the oscillation frequency fL of the local oscillator 20 by ΔL in order to change the frequency of the transmission RF signal. In this case, since the values of the frequencies f1 and f2 increase by ΔL, the intensity of the first signal filtered by the bandpass filter 60 and the intensity of the second signal change and are not substantially the same. For this reason, the average value of the intensity of the first signal output from the filter unit 80 and the average value of the intensity of the second signal change to different values. The amplifier circuit 72 outputs a control signal for changing the center frequency f0 of the bandpass filters 30 and 60 so that these values are at the same level. As a result, the center frequency f0 of the bandpass filters 30 and 60 becomes a value of fL + ΔL.

  As described above, the filter circuit 100 can change the passband by automatically controlling the center frequency of the bandpass filter 30. When the oscillation frequency fL of the local oscillator 20 is changed, the filter circuit 100 follows the change and controls the center frequency f0 of the bandpass filters 30 and 60 to be equal to fL. Therefore, it is not necessary to perform the inspection for each filter circuit in consideration of the variation in the control voltage of the bandpass filter. Also, a design margin can be reduced. Further, even if there is a change in the center frequency f0 of the bandpass filter 30 or the oscillation frequency fL of the local oscillator 20 due to temperature or the like, the change is automatically compensated in the filter circuit 100.

  The intermediate signal generation unit 40 alternately switches and outputs a sine wave signal and a cosine wave signal based on the pulse signal. Thus, the modulator 50 alternately switches and outputs the first signal and the second signal, and the control signal generation circuit 70 receives the first signal and the second signal alternately switched. . For this reason, the control signal generation circuit 70 divides the two signals from the detection signal and compares the magnitudes of the signals more easily than when the two signals are input simultaneously. can do.

  In the modulators 10 and 50, the local signal L for modulation is generated by the common local oscillator 20. Thereby, the circuit scale of the filter circuit 100 can be reduced.

  The circuit scale of the filter circuit 100 can be reduced by using a common pulse signal for the generation of the IF signal in the intermediate signal generation unit 40 and the branch of the detection signal Vdet in the filter unit 80. Further, by dividing the detection signal Vdet into a detection signal Vdet1 of the first signal and a detection signal Vdet2 of the second signal based on the pulse signal, the intensity of the filtered first signal and the intensity of the second signal Can be easily compared.

  The filter unit 80 calculates an average value of the intensity of the filtered first signal and the intensity of the second signal. Accordingly, the amplifier circuit 72 can easily compare which of the filtered first signal and second signal is higher.

  Furthermore, by making the filter unit 80 a low-pass filter and making the frequency of the pulse signal higher than the cut-off frequency of the low-pass filter, the filter unit 80 has the intensity of the filtered first signal and the intensity of the second signal. Output the average value of each. In this way, the filter unit 80 can have a simple configuration.

  In the filter circuit 100, the passband widths of the bandpass filters 30 and 60 are smaller than the difference | f 2 −f 1 | between the frequency f 1 of the first signal output from the modulator 50 and the frequency f 2 of the second signal. As a result, noise other than the first signal and the second signal in the adjustment signal is attenuated by the bandpass filter 60, so that the error in detection of the signal intensity by the detection circuit 71 can be further reduced. As described above, the center frequency f0 of the bandpass filters 30 and 60 can be adjusted to the oscillation frequency fL with higher accuracy.

  In the second embodiment, the pass characteristics of the two band pass filters 30 and 60 need to be substantially the same. With respect to this, variation in pass characteristics of the two band pass filters can be minimized by forming the two band pass filters 30 and 60 in the same chip in a semiconductor process.

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention. For example, the configurations of the intermediate signal generation unit 40 and the modulators 10 and 50 do not have to be those shown in FIG. The DUTY ratio of the pulse signal output from the pulse signal source 90 need not be 50%.

  The control flow of the filter circuit shown in the first and second embodiments can be executed by the filter circuit as one of the control methods. For example, the control program may be executed by a computer having a filter circuit.

  In the above example, the program can be stored and supplied to a computer using various types of non-transitory computer readable media. Non-transitory computer readable media include various types of tangible storage media. Examples of non-transitory computer-readable media include magnetic recording media (for example, flexible disks, magnetic tapes, hard disk drives), magneto-optical recording media (for example, magneto-optical disks), CD-ROMs (Read Only Memory), CD-Rs, CD-R / W, semiconductor memory (for example, mask ROM, PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, RAM (Random Access Memory)) are included. The program may also be supplied to the computer by various types of transitory computer readable media. Examples of transitory computer readable media include electrical signals, optical signals, and electromagnetic waves. The temporary computer-readable medium can supply the program to the computer via a wired communication path such as an electric wire and an optical fiber, or a wireless communication path.

DESCRIPTION OF SYMBOLS 1 Filter circuit 2 Band pass filter 3 Adjustment signal generator 4 Band pass filter 5 Control signal generation circuit 10 Modulator 11, 12 Mixer 13 Phaser 14 Sigma adder 20 Local oscillator 30 Band pass filter 40 Intermediate signal generation part 41 CW Signal source 42 Resistance 43, 44 RF switch 45 90 degree hybrid circuit 50 Modulator 51, 52 Mixer 53 Phase shifter 54 Sigma adder 60 Band pass filter 70 Control signal generation circuit 71 Detection circuit 72 Amplification circuit 80 Filter units 81, 82 Switch 83, 84 Resistor 85, 86 Capacitor 90 Pulse signal source 100 Filter circuit

Claims (10)

A first bandpass filter having a changeable center frequency and filtering the input signal to output a first output signal;
An adjustment signal generator for generating an adjustment signal including a first signal of frequency f1 and a second signal of frequency f2,
A second bandpass filter having a changeable center frequency and filtering the adjustment signal to output a second output signal;
A control signal generating circuit for detecting the intensity of the second output signal and generating a control signal for controlling a center frequency of the first bandpass filter and the second bandpass filter according to the detection result; ,
A filter circuit comprising: The filter circuit further includes a pulse signal source that outputs a pulse signal,
The adjustment signal generator alternately switches the first signal and the second signal based on the pulse signal and outputs the first signal and the second signal as the adjustment signal.
The filter circuit according to claim 1. The filter circuit further includes a local oscillator that outputs a local signal having a frequency (f1 + f2) / 2,
The adjustment signal generator is configured to generate an intermediate signal by alternately switching a sine wave signal and a cosine wave signal of frequency | f2-f1 | / 2 based on the pulse signal;
A first modulator that modulates the intermediate signal with the local signal and outputs the adjustment signal;
The filter circuit according to claim 2. The filter circuit further includes a second modulator that modulates a baseband signal with the local signal and outputs the input signal.
The filter circuit according to claim 3. The control signal generation circuit divides the adjustment signal filtered by the second bandpass filter into the first signal and the second signal based on the pulse signal, Outputting the control signal by comparing magnitude and magnitude of the second signal;
The filter circuit according to any one of claims 2 to 4. The control signal generation circuit includes an average value calculation unit that calculates an average value of the first signal intensity and an average value of the second signal intensity divided based on the pulse signal;
A control circuit that outputs the control signal by comparing the magnitude of the average value of the first signal and the average value of the intensity of the second signal;
The filter circuit according to claim 5, comprising: The average value calculation unit is a low-pass filter, and the frequency of the pulse signal is higher than the cutoff frequency of the low-pass filter,
The filter circuit according to claim 6. The passband width of the second bandpass filter is less than | f2-f1 |
The filter circuit according to any one of claims 1 to 7. Filtering the input signal with a first bandpass filter having a changeable center frequency to output a first output signal;
Generating an adjustment signal including a first signal at frequency f1 and a second signal at frequency f2,
Filtering the input signal with a second bandpass filter having a changeable center frequency to output a second output signal;
Detecting the intensity of the second output signal, and generating a control signal for controlling a center frequency of the first bandpass filter and the second bandpass filter according to the detection result;
A method for controlling a filter circuit comprising: Filtering the input signal with a first bandpass filter having a changeable center frequency to output a first output signal;
Generating an adjustment signal including a first signal at frequency f1 and a second signal at frequency f2,
Filtering the input signal with a second bandpass filter having a changeable center frequency to output a second output signal;
Detecting the intensity of the second output signal, and generating a control signal for controlling a center frequency of the first bandpass filter and the second bandpass filter according to the detection result;
Filter circuit control program for causing the filter circuit to execute.

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