JP2507944Y2 - FM radio receiver - Google Patents

Description

[Detailed description of the device]

[0001]

This invention relates to a double superheterodyne FM having a first intermediate frequency amplifying stage and a second intermediate frequency amplifying stage having a frequency band narrower than that of the first intermediate frequency amplifying stage. In a radio receiver, interference interference can be reduced by changing the center frequency and pass band (selectivity) of the second intermediate frequency amplification stage according to the signal level of the receiving station and the signal level of the adjacent station. With an adaptive tracking filter FM demodulator,
The present invention relates to stabilizing the passband switching operation by providing a hysteresis characteristic for detecting the signal level of the adjacent station, and especially when switching the channel selection, the detection of the signal level of the adjacent station is initialized to prevent malfunction of the passband switching. The present invention relates to an FM radio receiver designed to be prevented.

[0002]

2. Description of the Related Art A double superheterodyne FM radio receiver having an adaptive tracking filter FM demodulator in a second intermediate frequency amplification stage is known. The adaptive tracking filter FM demodulation device changes the center frequency of the filter of the second intermediate frequency amplification stage according to the modulation displacement of the selected signal, and the second intermediate frequency amplification according to the level of interference from the adjacent station. By changing the stage selectivity, interference from adjacent stations is reduced.

An FM radio receiver equipped with this adaptive tracking filter FM demodulator is extremely effective for receiving a desired station in a region where broadcasting stations are close to each other, such as Europe.

In a portable or vehicle-mounted receiver, radio waves from a distant broadcasting tower may reach and be disturbed while moving in a mountainous area. In such a case, adaptive tracking is also performed. The filter FM demodulator has a great effect.

FIG. 3 is an overall block diagram of a conventional double superheterodyne FM radio receiver provided with an adaptive tracking filter FM demodulator in a second intermediate amplification stage. The conventional FM radio receiver 101 amplifies the signal received by the receiving antenna 2 by the high frequency signal amplifier circuit 3,
The output signal 3a and the first local oscillation circuit 4 generated first
The local oscillation frequency signal 4a is mixed by the first mixing circuit 5, and the first intermediate frequency signal 5 having a frequency of 10.7 MHz, for example, is mixed.
a and supplies this signal 5a to a first intermediate frequency amplification stage 6 equipped with a fixed pass band intermediate frequency filter having a predetermined frequency bandwidth, and outputs its output, a first intermediate frequency output signal 6a. It is supplied to the adaptive tracking filter FM demodulation device 102.

The tuning control unit 103, based on the tuning information 7a input from the tuning operation unit 7, converts the high frequency signal of the receiving station into the first intermediate frequency, which is the first local oscillation frequency. The designation information 103a is supplied to the first local oscillation circuit 4, and the first local oscillation circuit 4 generates the designated first local oscillation frequency signal 4a based on this information 130a.

The demodulation output (decoded output signal) 50a of the adaptive tracking filter FM demodulation device 102 is input to a frequency-multiplexed signal demodulation circuit 8 such as a stereo signal demodulation circuit,
In the case of stereo broadcasting reception, the left and right two-channel audio signals 8L and 8R are obtained, and in the case of frequency division multiplex broadcasting, traffic information broadcast on sub-channels, information relating to the identification code of the broadcasting station, etc. Switching to broadcasting of the main channel is performed by a signal selection circuit (not shown), the respective audio signals 8L, 8R (which may include digital signals) are power-amplified by the low-frequency amplifiers 9L, 9R, and then the speaker The respective electroacoustic transducers 10L and 10R are driven to reproduce audible sound. Further, the audio signals 8L and 8R are configured so that they can be supplied to other devices from an output section (not shown).

FIG. 4 is a block diagram of a conventional adaptive tracking filter FM demodulator. This adaptive tracking filter FM demodulation device 102 includes an AGC circuit 2
1, a second local oscillation circuit 22, a second mixing circuit 23,
It comprises a second intermediate frequency amplification stage 130 having an adaptive tracking filter circuit 31 and a second intermediate frequency signal demodulation section 50.

The second intermediate frequency amplification stage 130 includes an adaptive tracking filter circuit 31, an AGC control circuit 32, and
The reception station signal level detection circuit 33, the adjacent station signal extraction circuit 34, the adjacent station signal level detection circuit 35, and the filter control unit 40. The filter control unit 40 includes a tracking control circuit 41 that controls the center frequency of the adaptive tracking filter circuit 31, a pass band control circuit 42 that controls the signal pass band of the adaptive tracking filter circuit 31, and an adjacent interference detection circuit 43. Equipped with.

The second intermediate frequency signal demodulating section 50 includes a second intermediate frequency signal demodulating circuit 51 for demodulating the output signal 30a of the second intermediate frequency amplifying stage 130 and a frequency characteristic correcting circuit 52.
And an amplitude limiting circuit 53, and outputs a composite output signal 50a.

In the AGC circuit 21, the amplification amount or the attenuation amount is the AGC signal 3 output from the AGC control circuit 32.
It is configured to be variable based on 2a, and the level of the first intermediate frequency signal 21a supplied to the second mixing circuit 23 is configured to be substantially constant.

The second local oscillator circuit 22 has, for example, a frequency of 1
Generate a second local oscillation frequency signal 22a of 0 MHz,
It is supplied to the second mixing circuit 23. The second mixing circuit 23 mixes the level-adjusted first intermediate frequency signal 21a and the second local oscillation frequency signal 22a so that the intermediate frequency is, for example, 7
It is converted to the second intermediate frequency signal 23a of 00 KHz. The second intermediate frequency signal 23a is input to the adaptive tracking filter circuit 31.

The adaptive tracking filter circuit 31 includes
It has a function of continuously varying the center frequency of the filter and a function of switching the pass band width with respect to the center frequency in, for example, six stages.

The filter center frequency can be changed by changing the capacitances of a plurality of variable capacitance diodes provided in the filter circuit based on the tracking control voltage signal 41a for controlling the center frequency output from the tracking control circuit 41. Done.

The switching of the pass band width is performed by the pass band designation information output from the pass band control circuit 42 (for example, parallel 5
It is performed by changing the resistance value for selectivity adjustment connected in parallel to the coil in the filter circuit based on the bit information 42a.

This adaptive tracking filter circuit 31
Has four sets of filter circuits connected in series. The center two frequencies of the filter circuits in the front two stages are mainly used for tracking control, and the filter circuits in the rear two stages mainly switch the pass band width. Is configured as follows.

Further, the adaptive tracking filter circuit section 31 outputs the signal passed through the filter circuit section of the previous two stages from the terminal 231 and the signal output from the terminal 31b passes through the filter sections of the front and rear stages. It is configured to switch between the selected signal and the signal that has passed only the filter units of the previous two stages, based on the filter stage number designation information included in the pass band designation information 42a.

The second intermediate frequency signal demodulating section 51 demodulates the second intermediate frequency signal 30a output from the output terminal 31b of the adaptive tracking filter circuit 31. The demodulated detection output 51a is supplied to the tracking control circuit 41, the frequency characteristic correction circuit 52, and the adjacent interference detection circuit 43.

The tracking control circuit 41 detects the detection output 5
A high-frequency emphasizing circuit for emphasizing the high-frequency component of 1a, a phase inverting circuit for generating a signal obtained by inverting the phase of the output signal of the high-frequency emphasizing circuit, and a smoothing circuit for smoothing the phase-inverted output with a predetermined time constant. And outputs the smoothed output as the tracking control voltage signal 41a.

Further, the tracking control circuit 31 is
The tracking operation mode in which the tracking control voltage is varied according to the detection output 51a and the tracking stop mode in which a preset fixed voltage related to the center frequency of the filter is output are set to the tracking on / off control signal 42.
It is configured to switch based on b.

Further, in the tracking operation mode, the tracking control circuit 41 allows a wide range of frequencies in which the center frequency of the filter is varied according to the detection output 51a based on the tracking range switching signal 42c. It is configured to switch to a relatively narrow range. The tracking range is switched by adjusting the gain of the feedback control loop based on the tracking range switching signal 42c.

The frequency characteristic correction circuit 52 is provided with a peaking circuit for emphasizing the high frequency component of the detection output 51a of the second intermediate frequency signal 30a narrowed by the adaptive tracking filter circuit 31. , Emphasizes high-frequency components of main channel signals and sub-channel signals. The peaking frequency is the frequency of the sub-carrier (67 KHz in the US, 57 KHz in Europe, stereo broadcasting in Japan 3
8 KHz) is commonly used.

Detection output 52a with corrected frequency characteristics
Of the output signal (MPXO
UT) 50a. It should be noted that this amplitude limiting circuit 53, based on the amplitude limiting on / off signal 42d,
When the degree of adjacent interference, which will be described later, is large and the detected output is excessive, the amplitude limiting operation is performed to suppress the excessive output.

The AGC control circuit 32 performs an envelope detection circuit 32b for performing an envelope detection of the relatively wide band second intermediate frequency signal output from the intermediate output terminal 31a of the adaptive tracking filter circuit 31. And the envelope detection output 32c is smoothed with a predetermined time constant to obtain the AGC signal 3
A smoothing circuit 32d for generating 2a is provided. AGC signal 3
2a is supplied to the AGC circuit 21 and the receiving station signal level detecting circuit 33, and the envelope detection output 32c is supplied to the adjacent station signal extracting circuit 34.

The receiving station signal level detection circuit 33 is an AGC.
Based on the signal 32a, information 33a, 33b relating to the magnitude of the reception level of the receiving station (desired station) is provided to the pass band control circuit 42
For example, two sets of voltage comparators having different threshold voltages are provided, and the comparison output of each comparator is output as the information 33a and 33b relating to the magnitude of the reception level to thereby obtain the level of the reception signal. It is configured to be divided into three stages of large, medium and small.

Each voltage comparator has a hysteresis characteristic. Each of the voltage comparators has a preset detection threshold value and a non-detection threshold value smaller than the detection threshold value.
a and 33b are configured to be held until the AGC signal 32a becomes equal to or lower than the non-detection threshold value.

The adjacent station signal extraction circuit 34 includes a high pass filter (HPF) 34a, an envelope detection circuit 34b, and a smoothing circuit 34c. The high-frequency component is extracted from the detection output 32c of the envelope detection circuit 32b in the AGC control circuit 32 via the high-pass filter 34a, and the extracted high-frequency component is again envelope-detected by the envelope detection circuit 34b, By smoothing with the smoothing circuit 34c, the voltage output 34d corresponding to the level of the signal adjacent to the receiving station (desired station) is obtained.

The adjacent station signal level detection circuit 35, based on the voltage output 34d from the adjacent station signal extraction circuit 34, information 35a, 35b, 3 regarding the magnitude of the reception level of the adjacent station.
5c and 35d are supplied to the pass band control circuit 42. For example, four sets of voltage comparators having different threshold voltages are provided, and the comparison output of each comparator is set to the level of (interfering) signal level of the adjacent station. By outputting as the information 35a to 35d, the level of the interfering signal due to the signal of the adjacent station is divided into five levels.

Each voltage comparator has a hysteresis characteristic. Each voltage comparator has a detection threshold value set in advance and a non-detection threshold value smaller than the detection threshold value.
a to 35d are configured to be held until the voltage output 34d corresponding to the level of the adjacent signal becomes equal to or lower than the non-detection threshold value.

The adjacent interference detection circuit 43 includes a low pass filter (LPF) 43a for extracting frequency components below the subcarrier frequency from the detection output 51a demodulated by the second intermediate frequency signal demodulation circuit 51, The low-pass filter (LPF) 43a is provided with an interference sound detection circuit 43b that generates a logical output 43c for adjacent interference detection when the output exceeds a preset threshold level. The disturbing sound detection circuit 43b is composed of a voltage comparator having a preset threshold voltage. The interference sound detection output 43c is supplied to the pass band control circuit 42.

The pass band control circuit 42 includes information 33a and 33b relating to the signal level of the receiving station (desired station),
Information 35a to 35d relating to the (jamming) signal of the adjacent station and the adjacent jamming detection output 43c are used as control inputs, and information 42a designating the pass band of the adaptive tracking filter circuit 31 and ON / OFF of the tracking operation are set. The designated signal 42b and the tracking range switching signal 42c
And the amplitude limiting on / off signal 42d are output based on preset conditions.

FIG. 5 is an explanatory diagram showing the pass band variable characteristic of the adaptive tracking filter circuit which is the second intermediate frequency filter. This adaptive tracking filter circuit 31
5 can switch between six types of pass band widths A to F based on the pass band designation information 42a, as shown in FIG. Then, as shown in FIG. 5B, the pass band control circuit 34 sets the signal level (electric field strength) of the receiving station (desired station) and the interfering wave level (electric field strength of the interfering wave) from the adjacent station. Based on the S / N of the received signal, the control is performed so as to narrow the pass band of the second intermediate frequency signal as the interference increases.

Further, when the adjacent interference detection output 43c is input, the pass band control circuit 42 relates to the information 33a, 33b relating to the signal level of the receiving station in that state and the receiving level (interference signal level) of the adjacent station. Information 35a-35d
Compare with Then, when the level of the adjacent station signal is higher than the level of the receiving station signal by a predetermined level or more set in advance, the signal 42 for controlling the tracking operation to the off state.
By outputting "b" and stopping the tracking operation, the center frequency of the adaptive tracking filter circuit 31 is prevented from shifting to the adjacent station side having a large signal level, and the signal 42d relating to the amplitude limitation ON is output. , The output signal 40a is suppressed from becoming excessive due to the adjacent interference output.

Further, in the pass band control circuit 42, the levels of the adjacent signals 35a to 35d are the signal level 33 of the receiving station.
When it is sufficiently lower than a and 33b (when interference is not received), the tracking range switching signal 42c is output so as to widen the tracking range.

With the above-mentioned configuration, the conventional FM radio receiver 101 has the first intermediate frequency amplification stage (consisting of the first intermediate frequency amplification section 6 and the fixed intermediate frequency filter 7) and has a relatively wide predetermined frequency. Since the band is selected and the pass band is narrowed according to the degree of adjacent interference using the adaptive tracking filter 31 which is the second intermediate frequency amplification stage, interference interference from adjacent stations can be significantly reduced.

[0036]

The receiving station signal level detecting circuit 33 and the adjacent station signal level detecting circuit 35 have hysteresis in their input / output characteristics to output the information 33a33b, 35a to 35d related to the level of each signal. Is configured to stabilize. Further, the signal level of the adjacent station is detected based on the signal obtained by envelope detection of the high frequency component in the second intermediate frequency signal.

Therefore, when another broadcasting station is selected from the receiving state in which the information 35a to 53d corresponding to the level of the interference is received due to the interference from the adjacent station, a new channel is selected. When the reception level of the broadcasting station is lower than the signal level of the previous receiving station, or when the modulation deviation of the newly selected broadcasting station is large, the output level of the high frequency component extracted by the adjacent station signal extraction circuit 34 Does not become smaller than the width of the hysteresis and there is no adjacent interference, or even if the level of adjacent interference is reduced by one step or more, the outputs 35a to 35 of the adjacent station signal level detection circuit 35 are generated.
d may not change.

In such a case, the pass band control circuit 42
Controls the adaptive tracking filter 31 so that the pass band is narrowed, so that the reproduction frequency band is narrowed even though the reception state is good, and the erroneous operation of unnecessarily lowering the fidelity of the reproduced sound occurs. May occur.

The present invention has been made to solve such a problem, and its purpose is to eliminate an erroneous operation related to the signal level detection of an adjacent station and to perform reception and reproduction in an appropriate signal pass band. To provide a receiver.

[0040]

In order to solve the above-mentioned problems, an FM radio receiver according to the present invention is provided with an adjacent station based on an initialization signal externally provided to the front side of the adjacent-station signal level detection circuit. The present invention is characterized by comprising level switching means for switching the input signal level of the signal level detection circuit to a level at which no detection output is generated.

[0041]

The level switching means can set the level of the signal supplied to the adjacent station signal level detection circuit to a level at which the detection output does not occur, based on the initialization signal. Therefore, the detection output of the adjacent station signal level detection circuit can be once set to the non-detection state by applying the initialization signal to the level switching means when the channel selection is changed. Then, since the detection of the level of the adjacent station signal is started from the time when the initialization signal is released, it is possible to prevent erroneous detection due to the hysteresis characteristic.

[0042]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall block configuration diagram of an FM radio receiver according to the present invention, and FIG. 2 is a block configuration diagram of an adaptive tracking filter FM demodulation device having a function of canceling adjacent station signal level detection output. The FM radio receiver 1 according to the present invention differs from the conventional FM radio receiver 101 in the following points.

The tuning control unit 11 supplies the first local oscillation frequency designation information 11a to the first local oscillation circuit 4 based on the tuning information 7a input from the tuning operation unit 7, and
When the tuning operation is performed, the initialization signal 11b having a preset pulse width is output. If an output for muting the audio signal is provided when the tuning operation is performed, the mute output signal is set to the initialization signal 11
It may be used as b.

A level switching means 36 is provided between the AGC control circuit 32 and the adjacent station signal extraction circuit 34. When the initialization signal 11b is applied to the switching control terminal 36a, the level switching means 36 sufficiently lowers the level of the signal supplied to the adjacent station signal extraction circuit 34, and AGC control is performed in a state where the initialization signal 11b is not applied. The envelope detection output 32c of the circuit 32 is used as it is for the adjacent station signal extraction circuit 3
4 is configured to be supplied to.

The level of the signal supplied to the adjacent station signal extraction circuit 34 may be switched by a semiconductor switch circuit using a transistor or the like so that the envelope detection output supplied to the adjacent station signal extraction circuit 34 is cut off. Further, the input terminal of the adjacent station signal extraction circuit 34 may be connected to, for example, the ground potential or the like. Further, in order to shorten the response time of the adjacent station signal level detection after the initialization state is released, the signal level may be suppressed or fixed to a range in which the adjacent station signal level detection output does not occur.

Further, the level switching means may be provided between the adjacent station signal extraction circuit 34 and the adjacent station signal level detection circuit 35, and the high pass filter (in the adjacent station signal extraction circuit 35 shown in FIG. HPF) 35a and envelope detection circuit 3
5b or between the envelope detection circuit 35b and the smoothing circuit 35c.

With the above configuration, when the tuning operation is performed, the tuning control section 11 generates the initialization signal 11b,
The level switching circuit 36 sufficiently reduces the level of the signal supplied to the adjacent station signal extraction circuit 34 based on the initialization signal 11b. For this reason, the signal level of the output 34d of the adjacent station signal extraction circuit 34 also decreases, and the detection outputs 35a to 35d of the adjacent station signal level detection circuit 35 are all not output.

When the initialization signal 11b is no longer supplied,
Since the level switching means 36 directly supplies the envelope detection output 32c of the AGC circuit 32 to the adjacent station signal extraction circuit 34, the adjacent signal for the newly selected receiving station is detected from this point. Therefore, the signal level detection result of the adjacent station in the previous reception state is not retained along with the hysteresis characteristic of level detection.

[0049]

As described above, the FM according to the present invention
The radio receiver is provided with level switching means for setting the level of the signal supplied to the adjacent station signal level detection circuit based on the initialization signal to a level at which the detection output does not occur. In order to prevent this, a signal for muting the audio signal output is supplied as an initialization signal to the signal level switching means to forcibly restore the detection output of the adjacent station signal level detection circuit to the state without interference detection. be able to.

Therefore, the degree of adjacent interference of the newly selected station can be accurately detected, and the signal pass band can be set according to the detection result, and the adjacent interference detection output in the previous reception state can be detected. It is held due to the hysteresis characteristic for stabilizing the operation, so that the signal pass band is narrowed and the fidelity of the reproduced sound is reduced even though the adjacent disturbance is not received or the level of the adjacent disturbance is small. It is possible to eliminate erroneous operation of decreasing.

[Brief description of drawings]

FIG. 1 is an overall block diagram of an FM radio receiver according to the present invention.

FIG. 2 is a block configuration diagram of an adaptive tracking filter FM demodulator having a built-in adjacent-station signal level detection output cancellation function.

FIG. 3 is an overall block configuration diagram of a conventional double superheterodyne FM radio receiver including an adaptive tracking filter FM demodulator in a second intermediate amplification stage.

FIG. 4 is a block configuration diagram of a conventional adaptive tracking filter FM demodulation device.

FIG. 5 is an explanatory diagram showing pass band variable characteristics of an adaptive tracking filter circuit which is a second intermediate frequency filter.

[Explanation of symbols]

1 ... FM radio receiver, 6 ... First intermediate frequency amplifier circuit, 6
a ... 1st intermediate frequency output signal, 7 ... tuning operation part, 11 ... tuning control part, 20 ... adaptive tracking filter FM demodulator, 30 ... 2nd intermediate frequency amplification stage, 32 ... AGC control circuit, 33 ... Receiver station signal level detection circuit, 33a, 33b
... Information (detection output) relating to signal level of receiving station, 34 ... Adjacent station signal extraction circuit, 35 ... Adjacent station signal level detection circuit,
35a to 35d ... Information (detection output) related to the adjacent station signal level, 36 ... Level switching means.

Claims (1)

(57) [Scope of utility model registration request] 1. A second intermediate frequency amplification stage is provided with an adaptive tracking filter circuit capable of varying the pass band of the second intermediate frequency signal, and information relating to the reception station signal level detected by the reception station signal level detection circuit. , And a pass band control circuit that switches the pass band of the adaptive tracking filter circuit based on information related to the adjacent station signal level detected by the adjacent station signal level detection circuit, and the adjacent station signal level detection circuit Has a detection threshold and a non-detection threshold less than this detection threshold,
In a FM radio receiver of a double superheterodyne system having a hysteresis characteristic for holding the information on the once output adjacent signal level until the input signal level of this adjacent station signal level detection circuit becomes equal to or lower than the non-detection threshold value, A level switching means for switching the input signal level of the adjacent station signal level detection circuit to a level at which a detection output is not generated is provided on the preceding stage side of the adjacent station signal level detection circuit based on an initialization signal given from the outside. FM radio receiver characterized by.