JP2011234152A - Frequency control circuit and frequency control method, receiver and receiving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a frequency control circuit that is excellent for a countermeasure against interference.SOLUTION: The frequency control circuit comprises: a local oscillator 118; a mixer 103 mixing an input signal and a local oscillation signal from the local oscillator; a high frequency side band-variable band pass filter 111 and a low frequency side band-variable band pass filter 112 filtering an output of mixer 103; a subtractor calculating an intensity difference between passage signals of both band pass filters 111 and 112; an accumulation circuit accumulating an output of a subtractor and supplying the accumulation value to the local oscillator 118 as a correction signal indicating a correction amount of an oscillating frequency of the local oscillator; and a filter control device 115 narrowing, in cooperation, a pass band width of both band pass filters 111 and 112 when an absolute value of the difference calculated by the subtractor becomes not more than a reference level.

Description

  The present invention relates to a frequency control circuit and a frequency control method for automatically controlling a reception frequency, and further to a receiver and a reception method using the frequency control circuit or the frequency control method.

  In wireless communication, each modulated signal is assigned to a channel having a predetermined center frequency and bandwidth. The user adjusts the receiver and tunes the received signal of the receiver to a desired channel to receive the target modulation signal.

  The frequency of the received signal may not match the center frequency of the channel. In this case, the received signal cannot be demodulated as it is, or the demodulated signal is distorted. In order to solve such a problem, an automatic frequency control circuit that automatically controls the reception frequency has been proposed. The automatic frequency control circuit compensates for the frequency shift of the signal to be received and retunes.

An example of a receiver including an automatic frequency control circuit is disclosed in Patent Document 1.
As shown in FIG. 1 of the same publication, this receiver uses a pair of bandpass filters, measures the intensity of signals that have passed through each bandpass filter, finds the difference in the measured intensity, Is used to control the frequency of the local oscillation signal and hold the center frequency of the input signal at the position of the nominal center frequency.

Japanese Patent Application Laid-Open No. 07-147529

In the receiver described in Patent Document 1, the center frequency of the reception signal can be matched with the center frequency of the reception channel.
However, when noise and other signals exist in the vicinity of the reception channel and the signals are located in the pass band of the band pass filter, that is, when interference exists, the operation is not performed correctly.

  In addition, since adjacent signals change for each channel and for each reception environment, it is difficult to cope with the conventional configuration.

The present invention has been made in view of the above problems, and an object thereof is to provide a frequency control circuit and a frequency control method that are excellent in measures against interference.
Another object of the present invention is to provide a receiver and a reception method using the frequency control circuit and the frequency control method.

In order to achieve the above object, the frequency control circuit of the present invention includes:
An input means for inputting a received signal;
A local oscillator that outputs a local oscillation signal;
A mixer that mixes a signal input by the input means and a local oscillation signal output from the local oscillator;
Filter means composed of a plurality of filters whose passbands on the high frequency side and the low frequency side partially overlap;
Oscillating frequency control means for controlling the oscillating frequency based on the intensity of the passing signals of a plurality of filters constituting the filter means;
In parallel with the control of the oscillation frequency by the oscillation frequency control means, bandwidth changing means for narrowing the pass bandwidth of each of the plurality of filters,
It is characterized by providing.

  For example, the plurality of filters includes a high frequency side variable band band pass filter and a low frequency side variable band band pass filter, and the high frequency side variable band band pass filter and the low frequency side variable band band pass filter include: The passbands are variable, are controlled to have the same bandwidth, and have frequency characteristics that are symmetric with respect to the crossover frequency of the passbands.

  For example, it has reception frequency switching means for switching the oscillation frequency of the local oscillator, and the bandwidth changing means is the intensity of the passing signal of the high frequency side variable band-pass filter after the reception frequency is switched by the reception frequency switching means. And the passband widths of the high-frequency variable band-pass filter and the low-frequency variable band-pass filter are narrowed after the intensities of the passing signals of the low-frequency variable-band bandpass filter substantially match.

  A band pass filter that limits a signal band is disposed between the mixer and the filter, and a center frequency of a pass band of the band pass filter, the high frequency side variable band band pass filter, and the low frequency side variable band You may comprise so that the cross frequency of the pass band of a band pass band pass filter may be substantially equal.

  The bandwidth changing means, for example, a subtracting means for outputting a signal representing a difference between the intensity of the passing signal of the high-frequency side variable band-pass filter and the intensity of the passing signal of the low-frequency side variable band-band pass filter; Accumulating means for accumulating the output signal of the subtracting means, and supplying the accumulated value to the local oscillator as a correction signal indicating the correction amount of the oscillation frequency of the local oscillator; and the output signal of the subtracting means is the absolute value of the difference Bandwidth control means for narrowing the pass bandwidth of the high-frequency side variable band-pass filter and the low-frequency side variable band-pass filter when the signal becomes below the reference level.

  It is also possible to provide a receiver comprising demodulating means for demodulating the output signal of the mixer and the frequency control circuit having the above configuration.

The frequency control method of the present invention is
Mix the input signal and the local oscillation signal to output a mixed signal,
Extracting a frequency component of a first frequency band from the mixed signal;
Extracting a signal component of a second frequency band partially overlapping with the first frequency band from the mixed signal;
Controlling the frequency of the local oscillation signal based on the intensity of the extracted frequency component of the first frequency band and the intensity of the extracted frequency component of the second frequency band;
In parallel with the control of the frequency of the local oscillation signal, the bandwidth of the first frequency band and the bandwidth of the second frequency band are expressed as the first frequency band and the second frequency band. Narrowing while maintaining duplicates,
It is characterized by that.

  For example, the first frequency band and the second frequency band are controlled to have the same bandwidth and to maintain the cross frequency of the pass band at a constant value regardless of the bandwidth. It is desirable.

  The mixed signal may be demodulated and output while executing the frequency control method described above.

  According to the present invention, since the frequency of the local oscillation signal is controlled (adjusted) and the passband width is narrowed, noise can be removed even when the received signal contains noise.

It is a block diagram which shows the structure of the receiver which concerns on embodiment of this invention. It is a block diagram which shows the structure of the correction amount detector shown in FIG. (A)-(c) is a figure which shows the pass-band width PBU of U-VBPF, and the pass-band PBL of L-VBPF, (d) is a figure which shows a reception target signal. (A)-(g) is a figure for demonstrating reception operation | movement after reception channel switching. (A)-(h) is a figure for demonstrating reception operation after reception channel switching, and is a figure explaining operation | movement in case a noise signal exists in the vicinity of a reception target signal.

  Hereinafter, a receiver and a reception method including a frequency control circuit and a frequency control method excellent in interference countermeasures according to an embodiment of the present invention will be described.

  As shown in FIG. 1, a receiver 10 according to this embodiment includes an antenna 101, a tuning circuit 102, a mixer 103, a bandpass filter (BPF) 104, a demodulator 105, and a bandpass filter (BPF). 106, output amplifier 107, speaker 108, high frequency side band variable bandpass filter (U-VBPF) 111, low frequency side band variable bandpass filter (L-VBPF) 112, and high frequency side intensity detector 113 A low frequency side intensity detector 114, a filter controller 115, a correction amount detector 116, a limiter 117, a local oscillator 118, and a channel selector 121.

  The antenna 101 and the tuning circuit 102 are tuned to a radio signal having a frequency fr corresponding to the channel selected by the channel selector 121, and receive and amplify and output the tuned radio signal.

  The mixer 103 mixes the reception signal having the frequency fr output from the tuning circuit 102 and the local oscillation signal having the frequency fL supplied from the local oscillator 118, and mainly corresponds to the sum (fr + fL) of the frequencies of both signals. An intermediate frequency signal having an intermediate frequency (IF) corresponding to the frequency difference (fr−fL) is output.

  The band-pass filter (BPF) 104 is composed of an intermediate frequency band pass filter having a predetermined center frequency Fc and a predetermined pass bandwidth, and among the output signals of the mixer 103, an intermediate frequency signal having a center frequency fr-fL. And a signal having a center frequency fr + fL is attenuated.

  The demodulator 105 performs demodulation processing on the intermediate frequency signal that has passed through the BPF 104 and reproduces an audio signal.

  The band pass filter (BPF) 106 removes unnecessary signals contained in the reproduced audio signal and outputs the result.

  The output amplifier 107 amplifies the audio signal that has passed through the BPF 106 and outputs the amplified audio signal to the speaker 108.

  The speaker 108 converts the audio signal output from the output amplifier 107 into air vibration and emits sound.

  The high frequency side variable band band pass filter (U-VBPF) 111 and the low frequency side variable band band pass filter (L-VBPF) 112 are band paths that change the pass bandwidth in conjunction with each other according to the control of the filter controller 115. It is a filter.

  More specifically, as shown in FIGS. 3A to 3C, the U-VBPF 111 and the L-VBPF 112 are bandpasses having variable passbands and controlled to have the same bandwidth. It is a filter.

  Specifically, as shown in FIGS. 3A to 3C, the passband PBU of the U-VBPF 111 is located on the higher frequency side than the passband PBL of the L-VBPF 112, and the passbands PBU and PBL The widths are equal to each other.

  A part of the low frequency side of the pass band PBU of the U-VBPF 111 and a part of the high frequency of the pass band PBL of the L-VBPF 112 overlap.

  The maximum width of the passband PBU of the U-VBPF 111 and the maximum width of the passband PBL of the L-VBPF 112 are smaller than the bandwidth of one channel and are combined as shown in FIGS. 3 (a) and 3 (d). The size is set to cover the bandwidth of one channel.

  Furthermore, the pass band PBU of the U-VBPF 111 and the pass band PBL of the L-VBPF 112 have a symmetric inclination (frequency characteristic) with respect to the cross frequency of the pass bands PBU and PBL. The crossover frequency of the passbands PBU and PBL is preferably set equal to the center frequency Fc of the passband of the BPF 104.

  The minimum width of the passband PBU of the U-VBPF 111 and the minimum width of the passband PBL of the L-VBPF 112 are smaller than the bandwidth of one channel and are combined as shown in FIGS. 3 (c) and 3 (d). The size is set to sufficiently cover the main signal of one channel.

  Further, the U-VBPF 111 and the L-VBPF 112 can change the pass bandwidth as shown in FIGS.

  The U-VBPF 111 and the L-VBPF 112 are composed of, for example, an FIR (Finite Impulse Response) filter, an IIR (Infinite Impulse Response) filter, and the like, and are supplied from the filter controller 115. By taking and setting the filter coefficient, the propagation characteristic is changed.

  The high frequency side intensity detector 113 of FIG. 1 detects the signal intensity of the signal that has passed through the U-VBPF 111 and outputs a signal indicating the detected intensity to the correction amount detector 116.

  The low frequency side intensity detector 114 detects the signal intensity of the signal that has passed through the L-VBPF 112 and outputs a signal indicating the detected intensity to the correction amount detector 116.

  In response to the channel switching signal CS supplied from the channel selector 121, the filter controller 115 sets the pass bandwidths of the U-VBPF 111 and the L-VBPF 112 to the maximum pass bandwidth, and subsequently, the correction amount detector 116. In response to the bandwidth control start signal SB supplied from, the filter coefficient is controlled so that the passbands of the U-VBPF 111 and the L-VBPF 112 are narrowed to a predetermined bandwidth.

  The filter controller 115 does not change the passband PBL of the U-VBPF 111 and the passband PBL of the L-VBPF 112, and does not change the cross frequency of the pass bands PBU and PBL, and the pass bands PBU and PBL have the cross frequency. The passbands PBU and PBL are narrowed to a predetermined bandwidth while maintaining the relationship of having a symmetric inclination (frequency characteristic) with respect to the axis of symmetry. As the pass band PBU of the U-VBPF 111 and the pass band PBL of the L-VBPF 112 are narrowed, the center frequency of the pass band PBU decreases and the center frequency of the pass band PBL increases.

  The correction amount detector 116 detects the signal intensity detected by the high frequency side intensity detector 113, that is, the signal intensity of the signal that has passed through the U-VBPF 111, and the signal intensity detected by the low frequency side intensity detector 114, that is, L−. Based on the difference from the signal strength of the signal that has passed through the VBPF 112, a frequency correction signal indicating the control amount (change amount) ΔfL of the oscillation frequency of the local oscillator 118 is supplied to the local oscillator 118 via the limiter 117.

  Further, the correction amount detector 116 responds to the channel switching signal CS supplied from the channel selector 121, the signal intensity detected by the high frequency side intensity detector 113, that is, the signal intensity of the signal that has passed through the U-VBPF 111. When the difference between the signal intensity detected by the low frequency side intensity detector 114, that is, the signal intensity of the signal that has passed through the L-VBPF 112 becomes almost zero, the bandwidth control start signal SB is sent to the filter controller 115. Is output.

A configuration example of the correction amount detector 116 is shown in FIG.
As illustrated, the correction amount detector 116 includes a subtracter 161, an adder 162, and a buffer 163.

  The subtractor 161 calculates a difference between the signal level of the output signal of the low frequency side intensity detection circuit 114 from the signal level of the output signal of the high frequency side intensity detector 113 and outputs a signal having a signal level corresponding to the difference. That is, the subtractor 161 obtains the difference between the signal strength of the signal that has passed through the U-VBPF 111 and the signal strength of the signal that has passed through the L-VBPF 112, and outputs a signal having a signal level that represents the difference in signal strength.

  The adder 162 adds the output signal of the subtractor 161 and the output signal of the buffer 163, and outputs a correction signal ΔfL indicating the correction amount of the oscillation frequency of the local oscillator 118 to the limiter 117.

  The buffer (delay circuit) 163 delays the output signal of the adder 162 for a certain period and supplies it to the adder 162 as an added number.

  The adder 162, the subtracter 161, and the buffer 163 cooperate to constitute an accumulation circuit that calculates an accumulated value of the output signal of the subtracter 161.

  The controller 164 responds to the channel switching signal CS supplied from the channel selector 121 when the absolute value of the signal level of the signal output from the subtracter 161 becomes substantially zero level below the threshold, that is, U The bandwidth control start signal SB is output to the filter controller 115 when the signal strength of the signal that has passed through the −VBPF 111 and the signal strength of the signal that has passed through the L-VBPF 112 become substantially equal.

  The limiter 117 shown in FIG. 1 limits the correction amount ΔfL represented by the correction signal supplied from the correction amount detector 116 to a range of ± Δmax, and supplies it to the local oscillator 118.

  In the above configuration, the response speed for controlling the frequency of the local oscillator 118 is preferably faster than the speed at which the passband widths of the U-VBPF 111 and the L-VBPF 112 are narrowed. In other words, before completing the control of the oscillation frequency of the local oscillator 118, the speed of narrowing the pass bandwidth may be relatively slow to the extent that the process of narrowing the pass bandwidth of the U-VBPF 111 and the L-VBPF 112 is not completed. desirable.

  When the user designates a reception channel, the channel selector 121 designates the frequency fr to be tuned (received) in the tuning circuit 102 and designates the local oscillator 118 in order to receive a radio signal of the designated channel. The frequency fL (= fr−Fc) of the local oscillation signal necessary for receiving the radio signal of the selected channel is notified. Further, the channel selector 121 transmits a channel switching signal CS to the filter controller 115 and the controller 164 of the correction amount detector 116.

Next, the operation of the receiver 10 having the above configuration will be described.
In order to facilitate understanding, it is assumed that the receiver 10 is currently receiving and reproducing a radio signal of a certain channel.
In this state, it is assumed that the user instructs the channel selector 121 to receive the channel having the center frequency fr.

  In response to the instruction, the channel selector 121 instructs the tuning circuit 102 to receive the frequency fr, instructs the local oscillator 118 to oscillate frequency fL = (fr−Fc), and sends a channel switching signal to the filter controller 115 and the controller 164. Output CS.

In response to these instructions, first, the tuning circuit 102 switches the tuning frequency fr, tunes to the radio signal of the frequency fr, and takes it in.
Further, the local oscillator 118 changes the oscillation frequency to (fr-Fc) and outputs a local oscillation signal to the mixer 103. Note that Fc is the center frequency of the pass band of the BPF 104.

  The mixer 103 mixes the received signal with the center frequency fr from the tuning circuit 102 and the local oscillation signal fL supplied from the local oscillator 118, and the intermediate frequency signal with the center frequency Fc and the center frequency of 2 · fr-Fc. Output a signal.

  The BPF 104 extracts and outputs an intermediate frequency signal having a center frequency Fc from the signals output from the mixer 103, and removes a signal having a center frequency of 2 · f1-fc and a noise component.

  The demodulator 105 demodulates the intermediate frequency signal output from the BPF 104 and reproduces the baseband signal.

  The BPF 106 removes harmonic components contained in the baseband signal and outputs an audio signal component.

  The output amplifier 107 converts the audio signal component output from the BPF 106 into an air signal and outputs the air signal.

  On the other hand, in response to the channel switching signal CS, the filter controller 115 controls the bandwidths of the U-VBPF 111 and the L-VBPF 112 to the maximum width.

  In addition, the controller 164 of the correction amount detector 116 starts a timer in response to the channel switching signal CS and measures a certain waiting period.

  During this standby period, for example, the tuning operation of the tuning circuit 102 and the oscillation frequency of the local oscillator 118 are stabilized, and the bandwidths of the U-VBPF 111 and the L-VBPF 112 are stabilized.

  Also during this standby period, the intermediate frequency signal output from the BPF 104 is supplied to the U-VBPF 111 and the L-VBPF 112. The high frequency side intensity detector 113 measures the intensity of the signal that has passed through the U-VBPF 111 and outputs an intensity signal indicating the measured intensity. Similarly, the low frequency side intensity detector 114 measures the intensity of the signal that has passed through the L-VBPF 112 and outputs an intensity signal indicating the measured intensity.

  The subtracter 161 in the correction amount detector 116 takes the difference between the output signal of the high frequency side intensity detector 113 and the output signal of the low frequency side intensity detector 114. That is, the subtracter 161 obtains the difference between the signal strength of the signal that has passed through the U-VBPF 111 and the signal strength of the signal that has passed through the L-VBPF 112.

The adder 162 adds the output signal of the subtracter 161 and the output signal of the buffer 163, and outputs the result as a correction signal ΔfL having the accumulated value as the signal level.
The correction signal ΔfL is supplied to the local oscillator 118 via the limiter 117.

  The local oscillator 118 corrects the oscillation frequency fL according to the correction signal ΔfL supplied via the limiter 117. When the correction signal ΔfL is positive, the local oscillator 118 increases the oscillation frequency fL by ΔfL. When the correction signal ΔfL is negative, The oscillation frequency fL is decreased by ΔfL.

  When the timer finishes measuring the standby period, the controller 164 determines whether or not the absolute value of the output signal of the subtractor 162 has become equal to or less than the reference value. That is, the controller 164 determines whether or not the absolute value of the difference between the intensity of the signal that has passed through the U-VBPF 111 and the intensity of the signal that has passed through the L-VBPF 112 has become equal to or less than a reference value (approximately 0).

  In a state where the absolute value of the output signal of the subtractor 162 is approximately equal to or less than the reference value, the adder 162 continues to output the correction signal ΔfL having a substantially constant level. For this reason, the local oscillator 118 oscillates at a frequency obtained by correcting the frequency instructed from the channel selector 121 with the correction signal ΔfL, and supplies the local oscillation signal to the mixer 103.

  Furthermore, after measuring the standby period, the controller 164 outputs a bandwidth control start signal SB to the filter controller 115 when detecting that the absolute value of the output signal of the subtracter 162 is substantially zero below the reference value. .

In response to this bandwidth control start signal SB, the filter controller 115 is symmetric with respect to the passband PBU of the U-VBPF 111 and the passband PBL of the L-VBPF 112 with respect to the crossing frequency. While maintaining this characteristic, the pass bandwidth is gradually reduced.
During this time, the control of the local oscillation frequency fL of the local oscillator 118 is continued. Thus, after the channel is switched by the channel selector 121, the operation of controlling the oscillation frequency of the local oscillator 118 based on the intensity of the passing signal of the U-VBPF 111 and the L-VBPF 112 and the passing bandwidth of the U-VBPF 111 and the L-VBPF 112 are narrowed. The operation is executed in parallel.

  When the pass bandwidths of the U-VBPF 111 and the L-VBPF 112 reach a predetermined bandwidth, the change of the pass bandwidth is stopped.

  This completes the frequency control operation associated with the change of the reception channel.

  An example of the frequency control operation described above will be described in the case of receiving the signal shown in FIG.

In this example, as shown in FIG. 4A, it is assumed that the reception target signal ST is shifted from the center frequency fcc of the channel to the high frequency side by Δf for some reason.
In this state, when the channel selector 121 is instructed to receive this channel, the channel selector 121 instructs the local oscillator 118 the oscillation frequency fL (= fcc−Fc) determined by the center frequency fcc of the channel.

  The local oscillator 118 controls (adjusts) the oscillation frequency fL according to the instruction. At this stage, the positional relationship between the received signal after frequency conversion by the mixer 103 and the U-VBPF 111 and the L-VBPF 112 is the relationship shown in FIGS. 4A and 4B, and the U-VBPF 111 and the L-VBPF 112 The cross frequency of the pass band (= the center frequency Fc of the pass band of the BPF 104) matches the center frequency fcc of the reception channel.

In this case, as shown in FIG. 4C, most of the reception target signals enter the passband PBU of the U-VBPF 111.
For this reason, the output signal of the high frequency side intensity detector 113 is larger than the output signal of the low frequency side intensity detector 114, and the output signal of the subtractor 161 has a positive polarity (value). The adder 162 calculates the accumulated value of this output signal and outputs a positive correction signal ΔfL.

The correction signal ΔfL output from the adder 162 is supplied to the local oscillator 118 via the limiter 117. In response to the positive frequency correction signal ΔfL, the local oscillator 118 increases the oscillation frequency.
As a result, the frequency of the reception target signal ST after the frequency conversion gradually decreases as shown in FIGS. 4 (c), (d), and (e).

  When the frequency of the reception target signal ST after the frequency conversion becomes substantially equal to the center frequency Fc of the pass band of the BPF 104, as shown in FIG. 4 (e), the reception located in the pass band PBU of the U-VBPF 111 is received. The intensities of the target signal ST and the reception target signal ST located in the passband PBL of the L-VBPF 112 are substantially equal. The output signal of the high frequency side intensity detector 113 and the output signal of the low frequency side intensity detector 114 are substantially equal. For this reason, the output signal of the subtractor 161 is also substantially at the 0 level. The adder 162 is in a state where it continues to output a signal at a substantially constant level. The local oscillator 118 sets the oscillation frequency to a substantially constant value (fcc−Fc + Δf).

  When the controller 164 determines that the absolute value of the output of the adder 162 is equal to or less than the threshold value, the controller 164 outputs a bandwidth control start signal SB to the filter controller 115.

  In response to the bandwidth control start signal SB, the filter controller 115 adjusts the filter coefficients supplied to the U-VBPF 111 and the L-VBPF 112, as shown in FIGS. 4 (e) to 4 (g). The passband widths of the VBPFs 111 and 112 are gradually narrowed in cooperation.

  During this time, the control of the local oscillation frequency fL of the local oscillator 118 is continued. Thus, the operation of controlling the oscillation frequency of the local oscillator 118 and the operation of narrowing the pass bandwidth of the U-VBPF 111 and the L-VBPF 112 are executed in parallel.

  When the pass bandwidths of the U-VBPF 111 and the L-VBPF 112 reach a predetermined value, the control of the pass bandwidth ends.

  Next, the operation when the noise signal SN exists in the vicinity of the target signal ST will be described with reference to FIGS.

  First, as shown in FIG. 5A, it is assumed that the reception target signal ST is shifted from the center frequency fcc of the channel to the high frequency side by Δf for some reason, and the noise signal SN exists in the vicinity thereof. To do.

  In this state, when the channel selector 121 is instructed to receive this channel, the channel selector 121 instructs the local oscillator 118 the oscillation frequency fL (= fcc−Fc) determined by the center frequency fcc of the channel.

  The local oscillator 118 controls the oscillation frequency according to the instruction. At this stage, the positional relationship between the reception target signal ST and the noise signal SN after passing through the mixer 103 and the frequency conversion, the passband PBU of the U-VBPF 111 and the passband PBL of the L-VBPF 112 is as shown in FIG. The relationship shown in (b) is obtained. In this case, as shown in FIG. 5C, the reception target signal ST and the noise signal SN enter the pass band PBU of the U-VBPF 111 and the pass band PBL of the L-VBPF 112.

  At this stage, the received signal located in the passband PBU of the U-VBPF 111 and the received signal located in the passband PBL of the L-VBPF 112 are substantially equal in intensity, and the output signal of the high frequency side intensity detector 113 is The output signal of the low frequency side intensity detector 114 is substantially equal. For this reason, the output signal of the subtractor 161 is also substantially at the 0 level.

  For this reason, the frequency correction signal ΔfL output from the adder 162 has a substantially constant level. Therefore, the oscillation frequency of the local oscillator 118 becomes a substantially constant value.

  On the other hand, when the measurement of the standby period is completed, the controller 164 determines that the absolute value of the output of the adder 162 is equal to or less than the threshold value, and outputs the bandwidth control start signal SB to the filter controller 115. In response to the instruction, the filter controller 115 adjusts the filter coefficient supplied to the U-VBPF 111 and the L-VBPF 112, thereby passing the both VBPFs 111 and 112 as shown in FIGS. Reduce bandwidth gradually.

  During this time, the control of the local oscillation frequency fL of the local oscillator 118 is continued. Thus, the operation of controlling the oscillation frequency of the local oscillator 118 and the operation of cooperatively narrowing the pass bandwidths of the U-VBPF 111 and the L-VBPF 112 are executed in parallel.

  By narrowing the pass band width, the noise signal SN deviates from the pass band of the L-VBPF 112 as shown in FIG. 5D, while the reception target signal ST is located in the pass band PBU of the U-VBPF 111. .

  For this reason, the output signal of the high frequency side intensity detector 113 is larger than the output signal of the low frequency side intensity detector 114, and the output signal of the subtractor 161 has a positive polarity (value). The adder 162 obtains an accumulated value of this output signal and outputs a positive correction signal ΔfL. For this reason, the local oscillator 118 increases the oscillation frequency fL by ΔfL. Thereby, as shown in FIGS. 5C to 5G, the frequency of the reception target signal ST after the frequency conversion by the mixer 103 is gradually decreased. Further, as shown in FIGS. 5C to 5G, the pass bandwidths of the U-VBPF 111 and the L-VBPF 112 are gradually narrowed.

  Thus, as shown in FIG. 5 (g), the passband widths of the U-VBPF 111 and the L-VBPF 112 become predetermined values, and the frequency after frequency conversion of the reception target signal ST is equal to that of the U-VBPF 111 and the L-VBPF 112. A series of control is completed at the stage where the frequency coincides with the crossing frequency of the passband.

However, the operation of controlling the oscillation frequency fL of the local oscillator 118 is continued.
For this reason, when the frequency of the reception target signal ST is shifted as shown in FIG. 5 (h) for some reason (in the drawing, shifted to the low frequency side), the output of the subtracter 161 becomes negative and the addition is performed. The correction signal ΔfL output from the counter 162 becomes a negative value, the oscillation frequency is lowered, and it is possible to return to an appropriate reception state.

  As described above, according to the present embodiment, after selecting a channel, the oscillation frequency is controlled so that the amount (energy) of signals passing through the U-VBPF 111 and the L-VBPF 112 is the same, and then the oscillation is performed. In parallel with the operation of controlling the frequency, the pass bandwidths of the U-VBPF 111 and the L-VBPF 112 are narrowed. For this reason, it becomes possible to receive the target signal stably regardless of the frequency fluctuation of the reception target signal ST, and to eliminate noise.

In addition, this invention is not limited to the said embodiment, A various deformation | transformation and application are possible.
For example, various controls can be performed by a processor.

Further, the receiver 10 can be formed of an analog circuit or a digital circuit.
When formed by an analog circuit, for example, the amount of information is represented by the signal level (voltage level) of each signal.

  On the other hand, in the case of forming with a digital circuit, for example, i) the U-VBPF 111 to limiter 117 are constituted by a digital circuit such as a CPU (Central Processing Unit), DSP (Digital Signal Processor), and ii) the output of the BPF 104 is A / D (Analog to Digital) conversion and supply to the digital circuit, iii) The output of the limiter 117 in the digital circuit is D / A (Digital to Analog) converted and then supplied to the local oscillator 118. Good.

  In the above configuration, it has been described that the response speed for controlling the frequency of the local oscillator 118 is preferably faster than the speed at which the passband width of the U-VBPF 111 and the L-VBPF 112 is narrowed. However, the present invention is not limited to this. However, it may be set as appropriate according to the pass bandwidth and the like.

The configuration for controlling the frequency of the local oscillator 118 is not limited to the configuration shown in FIG. The configuration for controlling the frequency of the local oscillator 118 increases the oscillation frequency of the local oscillator 118 when the signal level detected by the high frequency side intensity detector 113 is higher than the signal level detected by the low frequency side intensity detector 114. When the signal level detected by the high frequency side intensity detector 113 is lower than the signal level detected by the low frequency side intensity detector 114, the oscillation frequency of the local oscillator 118 is lowered and the detection by the high frequency side intensity detector 113 is performed. Any configuration can be used as long as the oscillation frequency of the local oscillator 118 can be maintained when the signal level detected is equal to the signal level detected by the low frequency side intensity detector 114.
Further, for example, the buffer 163 may be reset by the channel switching signal CS.

  For example, the procedure for narrowing the pass band PBU of the U-VBPF 111 and the pass band PBL of the L-VBPF 112 is not limited to the above example.

  For example, in the above embodiment, after the channel is selected, the oscillation frequency of the local oscillator 118 is adjusted so that the signal level detected by the high frequency side intensity detector 113 and the signal level detected by the low frequency side intensity detector 114 are almost equal. After equalization, the pass bandwidths of U-VBPF 111 and L-VBPF 112 were narrowed. The present invention is not limited to this. For example, after a channel is selected, a predetermined time may be measured with a timer, and then the pass bandwidth of the U-VBPF 111 and the L-VBPF 112 may be narrowed. Further, after the channel is selected, the passband width of the U-VBPF 111 and the L-VBPF 112 may be gradually narrowed while adjusting the oscillation frequency of the local oscillator 118.

  Moreover, the example which adjusts a filter coefficient was shown as a structure which controls the pass-band width of U-VBPF111 and L-VBPF112. This invention is not limited to this, The structure which controls the pass-band width of U-VBPF111 and L-VBPF112 is arbitrary. What is necessary is just to select suitably according to the structure of U-VBPF111 and L-VBPF112.

  The configurations and numerical values shown in the above embodiment are merely examples, and the present invention is not limited thereto.

DESCRIPTION OF SYMBOLS 10 Receiver 101 Antenna 102 Tuning circuit 103 Mixer 104 Band pass filter (BPF)
105 Demodulator 106 Bandpass Filter (BPF)
107 Output Amplifier 108 Speaker 111 High Frequency Side Band Variable Bandpass Filter (U-VBPF)
112 Low-frequency band-variable bandpass filter (L-VBPF)
113 High Frequency Side Intensity Detector 114 Low Frequency Side Intensity Detector 115 Filter Controller 116 Correction Amount Detector 117 Limiter 118 Local Oscillator 121 Channel Selector 161 Subtractor 162 Adder 163 Buffer 164 Controller

Claims (9)

An input means for inputting a received signal;
A local oscillator that outputs a local oscillation signal;
A mixer that mixes a signal input by the input means and a local oscillation signal output from the local oscillator;
Filter means composed of a plurality of filters whose passbands on the high frequency side and the low frequency side partially overlap;
Oscillating frequency control means for controlling the oscillating frequency based on the intensity of the passing signals of a plurality of filters constituting the filter means;
In parallel with the control of the oscillation frequency by the oscillation frequency control means, bandwidth changing means for narrowing the pass bandwidth of each of the plurality of filters,
A frequency control circuit comprising: The plurality of filters are composed of a high frequency side variable band band pass filter and a low frequency side variable band band pass filter,
The high-frequency-side variable band-pass filter and the low-frequency-side variable-band band-pass filter are controlled so that their pass bandwidths are variable and have the same bandwidth, and the cross-band frequencies of the pass bands are symmetrical axes Have symmetrical frequency characteristics,
The frequency control circuit according to claim 1. Receiving frequency switching means for switching the oscillation frequency of the local oscillator;
The bandwidth changing means, after switching the reception frequency by the reception frequency switching means, the intensity of the passing signal of the high frequency side variable band band pass filter and the intensity of the passing signal of the low frequency side variable band band pass filter are substantially the same. After
Narrow the passband width of the high frequency side variable band bandpass filter and the low frequency side variable band bandpass filter,
The frequency control circuit according to claim 2. Between the mixer and the filter, a band pass filter that limits a signal band is provided,
The center frequency of the pass band of the band pass filter and the cross frequency of the pass band of the high frequency side variable band band pass filter and the low frequency side variable band band pass filter are substantially equal.
The frequency control circuit according to claim 3. The bandwidth changing means includes
Subtracting means for outputting a signal representing the difference between the intensity of the passing signal of the high frequency side variable band bandpass filter and the intensity of the passing signal of the low frequency side variable band bandpass filter;
Accumulating means for accumulating the output signal of the subtracting means and supplying the accumulated value to the local oscillator as a correction signal indicating a correction amount of the oscillation frequency of the local oscillator;
When the output signal of the subtracting means becomes less than the reference level absolute value of the difference,
Bandwidth control means for narrowing the passband width of the high-frequency side variable band-pass filter and the low-frequency side variable band-pass filter;
The frequency control circuit according to claim 2, comprising: Demodulation means for demodulating the output signal of the mixer;
A receiver comprising: the frequency control circuit according to claim 1. Mix the input signal and the local oscillation signal to output a mixed signal,
Extracting a frequency component of a first frequency band from the mixed signal;
Extracting a signal component of a second frequency band partially overlapping with the first frequency band from the mixed signal;
Controlling the frequency of the local oscillation signal based on the intensity of the extracted frequency component of the first frequency band and the intensity of the extracted frequency component of the second frequency band;
In parallel with the control of the frequency of the local oscillation signal, the bandwidth of the first frequency band and the bandwidth of the second frequency band are expressed as the first frequency band and the second frequency band. Narrowing while maintaining duplicates,
A frequency control method characterized by the above. The first frequency band and the second frequency band have the same bandwidth, and control so that the crossing frequency of the pass band is maintained at a constant value regardless of the bandwidth,
The frequency control method according to claim 7. A frequency control method according to claim 7 or 8,
Demodulating and outputting the mixed signal;
A receiving method comprising:

Images