JPH053443A - Fm radio receiver - Google Patents

Abstract

(57) [Abstract] [Purpose] A double superheterodyne F having a first intermediate frequency amplification stage and a second intermediate frequency amplification stage having a frequency band narrower than that of the first intermediate frequency amplification stage.
(EN) Provided is an FM radio receiver capable of reproducing with high fidelity in an M radio receiver in a good reception state in which no adjacent interference is received. A demodulation signal selection control circuit 13 is provided with a first intermediate frequency signal demodulation unit 11 and a second intermediate frequency signal demodulation unit 35 that demodulate the output signals 7a and 35a of the first and second intermediate frequency amplification stages, respectively. The demodulation signal selection circuit 13 selects the demodulation output 11a of the first intermediate frequency signal demodulation unit 11 when the reception state is good based on the outputs of the signal level detection circuits 30 and 32 of the reception station and the adjacent station. Control.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present 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. Radio receiver, second
The present invention relates to a device provided with an adaptive tracking filter FM demodulation device capable of reducing interference by changing the center frequency and selectivity of the intermediate frequency amplification stage, especially when the reception condition of the selected radio wave is good. , The demodulation output of the first intermediate frequency amplification stage with a wide frequency band is automatically selected,
The present invention relates to an FM radio receiver adapted to reproduce an audible sound.

[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 demodulator 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 selectivity of the stage, 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 in the first mixing circuit 5, and the first intermediate frequency signal 5 having a frequency of 10.7 MHz is mixed, for example.
a, the signal 5a is amplified by the first intermediate frequency amplifier circuit 6, and the amplified output 6a is supplied to a fixed pass band type intermediate frequency filter 7 having a predetermined frequency bandwidth. Through the first intermediate frequency output signal 7a
To the adaptive tracking filter FM demodulator 102.

The demodulation output 102a 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, and in the case of stereo broadcast reception, left and right two-channel audio signals 8L and 8R are obtained. Further, in the case of frequency division multiplex broadcasting, switching between the traffic information broadcast on the sub-channel, the information related to the identification code of the broadcasting station, and the broadcasting of the main channel is performed by a signal selection circuit (not shown), Each of these audio signals 8L, 8R
Each low-frequency amplifier 9 (may include a digital signal)
The power is amplified by L and 9R and each electroacoustic transducer 10L and 10R such as a speaker is driven to reproduce an audible sound. Also,
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. The adaptive tracking filter FM demodulator 102 includes a voltage control type attenuator 21, a second local oscillation circuit 22, and a second mixing circuit 2.
3, an adaptive tracking filter circuit 24, a second intermediate frequency signal demodulation circuit 25, and a tracking control circuit 26.
A frequency characteristic correction circuit 27, an amplitude limiting circuit 28,
AGC control circuit 29 and receiving station signal level detection circuit 30
, An adjacent station signal extraction circuit 31, an adjacent station signal level detection circuit 32, an adjacent interference detection circuit 33, and a pass band control circuit 34.

The voltage control type attenuator 21 has an attenuation amount of A
The second mixing circuit 23 is configured to be variable based on the AGC signal 29a output from the GC control circuit 29.
It is configured so that the level of the first intermediate frequency signal 21a supplied to

The second local oscillator circuit 22 has, for example, a frequency of 1
Generating 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 7
It is converted into the second intermediate frequency signal 23a of 00 KHz. The second intermediate frequency signal 23a is input to the adaptive tracking filter circuit 24.

The adaptive tracking filter circuit 24 is
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 26a for controlling the center frequency output from the tracking control circuit 26. Done.

The switching of the pass band width is performed by the pass band designation information output from the pass band control circuit 34 (for example, parallel 5
This is done by changing the resistance value for selectivity adjustment connected in parallel to the coil in the filter circuit based on the bit information) 34a.

This adaptive tracking filter circuit unit 2
4 has four sets of filter circuits connected in series.
The center-frequency tracking control is mainly performed in the filter circuit section of the second stage, and the pass band width is mainly switched in the filter circuit section of the latter two stages.

Further, the adaptive tracking filter circuit section 24 outputs the signal which has passed through the filter circuits of the previous two stages from the terminal 24a, and the signal which is output from the terminal 24b through the filter units of the front and rear two 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 33a.

The second intermediate frequency signal demodulating section 25 demodulates the signal output from the output terminal 24b of the adaptive tracking filter circuit 24. The demodulated detection output 25a is
Tracking control circuit 26 and frequency characteristic correction circuit 2
7 and the adjacent interference detection circuit 33.

The tracking control circuit 26 detects the detection output 2
A high-frequency emphasis circuit for emphasizing the high-frequency component of 5a, a phase inversion circuit for generating a signal obtained by inverting the phase of the output signal of the high-frequency emphasis circuit, and a smoothing circuit for smoothing the phase inversion output with a predetermined time constant. And outputs the smoothed output as the tracking control voltage signal 26a.

Further, the tracking control circuit 26 is
The tracking operation mode in which the tracking control voltage is varied according to the detection output 25a 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 34.
It is configured to switch based on b.

Further, in this tracking operation mode, the tracking control circuit 26 allows a wide range of frequencies in which the center frequency of the filter is varied according to the detection output 25a based on the tracking range switching signal 33c. 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 34c.

The frequency characteristic correction circuit 27 includes a peaking circuit for emphasizing the high frequency component of the detection output 25a of the second intermediate frequency signal narrowed by the adaptive tracking filter circuit 24. The high frequency component of the main channel signal and the sub channel signal are emphasized. The peaking frequency is the frequency of the sub-carrier (US 67K
Hz, Europe 57KHz, Japanese stereo broadcasting 38KHz
Etc. are generally used.

Detection output 27a with corrected frequency characteristics
Is transmitted via the amplitude limiting circuit 28 to the decoding output signal (MPXO
UT) is output. The amplitude limiting circuit 28
On the basis of the amplitude limiting on / off signal 34d, when the degree of adjacent interference, which will be described later, is large and the detection output is excessive, the amplitude limiting operation is performed to suppress the excessive output.

The AGC control circuit 29 performs an envelope detection circuit 29b for performing an envelope detection of the relatively wide band second intermediate frequency signal output from the intermediate output terminal 24a of the adaptive tracking filter circuit 24. And the envelope detection output 29c is smoothed with a predetermined time constant to obtain the AGC signal 2
A smoothing circuit 29d for generating 9a is provided. AGC signal 2
9a is supplied to the voltage control type attenuator 21 and the reception station signal level detection circuit 30, and the envelope detection output 29c is supplied to the adjacent station signal extraction circuit 31.

The receiving station level detecting circuit 30 supplies information 30a and 30b relating to the receiving level of the receiving station (desired station) to the pass band control circuit 34 based on the AGC signal 29a. By providing two sets of voltage comparators having different value voltages and outputting the comparison output of each comparator as the information 30a, 30b relating to the magnitude of the reception level, the level of the reception signal is divided into three stages of large, medium and small. I am configuring.

The adjacent station signal extraction circuit 31 includes a high pass filter (HPF) 31a, an envelope detection circuit 31b, and a smoothing circuit 31c. The high-frequency component is extracted from the detection output 29c of the envelope detection circuit 29b in the AGC control circuit 29 through the high-pass filter 31a, and the extracted high-frequency component is again envelope-detected by the envelope detection circuit 31b. By smoothing by the smoothing circuit 31c, the voltage output 31d corresponding to the level of the signal adjacent to the receiving station (desired station) is obtained.

The adjacent station level detection circuit 32, based on the voltage output 31d from the adjacent station signal extraction circuit 31, information 32a, 32b, 32 relating to the magnitude of the reception level of the adjacent station.
c and 32d are supplied to the pass band control circuit 34,
For example, four sets of voltage comparators having different threshold voltages are provided, and the comparison output of each comparator is output as the information 30a to 30d relating to the magnitude of the interfering signal level, whereby the level of the interfering signal by the signal of the adjacent station is obtained. Is divided into 5 stages.

The adjacent interference detection circuit 33 includes a low pass filter (LPF) 33a for extracting frequency components below the subcarrier frequency from the detection output 25a demodulated by the second intermediate frequency signal demodulation circuit 25, The low-pass filter (LPF) 33a includes an interference sound detection circuit 33b that generates a logical output 33c related to adjacent interference detection when the output exceeds a preset threshold level. The disturbing sound detection circuit 33b is composed of a voltage comparator having a preset threshold voltage. The interference sound detection output 33c is supplied to the pass band control circuit 34.

The pass band control circuit 34 includes information 30a and 30b relating to the signal level of the receiving station (desired station),
Information 31a to 31d related to (interference) signals of adjacent stations and the adjacent interference detection output 33c are used as control inputs, and information 34a designating the pass band of the adaptive tracking filter circuit 24 and ON / OFF of the tracking operation are set. The designated signal 34b and the tracking range switching signal 34c
And the amplitude limiting on / off signal 34d 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 24
Can switch between six types of pass band widths A to F, as shown in FIG. 5A, based on the pass band designation information 34a. 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 interference wave level (electric field strength of the interference 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.

When the adjacent interference detection output 33c is input, the pass band control circuit 34 outputs information 30a and 30b relating to the signal level of the receiving station in that state and information 32a to 32d relating to the receiving level of the adjacent station. Compare. 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, a signal 34b for controlling the tracking operation to the off state is output to stop the tracking operation. The center frequency of the tracking filter circuit 24 is prevented from shifting to the adjacent station side where the signal level is large, and the signal 34d relating to the ON of the amplitude limitation is output, so that the decoding output signal 8a becomes excessive due to the adjacent interference output. Suppress.

Further, in the pass band control circuit 34, the levels of the adjacent signals 30a to 32d are the signal level 30 of the receiving station.
When it is sufficiently lower than a and 30b (when interference is not received), the tracking range switching signal 34c 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 (which is composed of the first intermediate frequency amplification unit 6 and the fixed intermediate frequency filter 7) and is relatively wide and predetermined. Since the band is selected and the pass band is narrowed according to the degree of adjacent interference by using the adaptive tracking filter 24 which is the second intermediate frequency amplification stage, interference interference from adjacent stations can be significantly reduced.

[0031]

As described above,
The FM radio receiver 101 of the conventional double superheterodyne system has a configuration in which the pass band of the signal is narrowed by using the second intermediate frequency amplification stage to improve the selectivity, and therefore the second intermediate frequency signal demodulation circuit 25 demodulates. Frequency characteristic correction circuit 2 having a peaking circuit for the high frequency component of the detected detection output 25a
Even if emphasized in 7, the frequency characteristic of the detection output 25a is different from that of the original signal, so that the fidelity of the reproduced sound is lowered even in a good reception state where no adjacent interference is received.

Further, since the frequency characteristic correction circuit 27 has a structure for emphasizing high frequency components, when the modulation frequency of the received signal is high (there are many high frequency components of the audio signal), the harmonics generated by demodulation are generated. The frequency component of is also high, and the harmonic component reaches the peaking frequency region. Therefore, the frequency characteristic correction circuit 27 emphasizes an originally unnecessary noise component, the distortion rate of the composite output signal MPXOUT decreases, and the fidelity of reproduced sound is impaired.

The present invention has been made to solve the above problems, and an object thereof is to provide an FM radio receiver capable of high-fidelity reproduction in a good reception state in which adjacent interference is not received. To do.

[0034]

In order to solve the above-mentioned problems, an FM radio receiver according to the present invention demodulates an output signal of a first intermediate frequency amplification stage to output a wideband demodulated signal.
An intermediate frequency signal demodulation unit, a second intermediate frequency signal demodulation unit that demodulates the output signal of the second intermediate frequency amplification stage and outputs a narrow band demodulation signal, and a demodulation that selects one of these two demodulation signals A signal selection circuit, a reception station signal level detection circuit for detecting a signal level of a reception station based on a signal component of a second intermediate frequency signal of the second intermediate frequency amplification stage, and a second intermediate frequency of the second intermediate frequency amplification stage Adjacent station signal level detection circuit that detects the signal level of the adjacent station based on the high-frequency signal component of the signal, and the signal level of the receiving station is higher than the preset received signal level and the signal level of the adjacent station is preset A demodulation signal selection control means for controlling the demodulation signal selection circuit so as to select a wideband demodulation signal in a reception state smaller than the disturbing signal level and a narrowband demodulation signal in other reception states. And it features.

[0035]

[Operation] In a good reception condition without interference,
A wideband demodulated signal obtained by demodulating the first intermediate frequency signal having a wide signal pass band is automatically selected. Therefore, it is possible to perform reproduction with high fidelity in a good reception state in which no adjacent interference is received.

[0036]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall block diagram of an FM radio receiver according to the present invention. The FM radio receiver 1 according to the present invention is different from the conventional FM radio receiver 101 in that
A first intermediate frequency signal demodulation section 11 for demodulating an output signal 7a of a first intermediate frequency stage, which includes a first intermediate frequency amplifier circuit 6 and an intermediate frequency filter 7 of fixed signal pass band, and the first intermediate frequency signal demodulation Wideband demodulated signal 11a demodulated by the unit 11 and the adaptive tracking filter FM demodulator 1
In the adaptive tracking filter FM demodulation device 12, a demodulation signal selection circuit 13 that selects either one of the two demodulation signals, the narrow band demodulation signal 35a demodulated by the second intermediate frequency signal demodulation unit 35 The demodulation signal selection control means 14 for generating the demodulation signal selection control signal 14a based on the signal detection outputs 30a, 30b, 32a to 32d of the reception station signal level detection circuit 30 and the adjacent station signal level detection circuit 32 is newly added. Be prepared.

The structure of the adaptive tracking filter FM demodulator 12 constituting the second intermediate frequency amplification stage is basically the same as that shown in FIG. 4, and the detection output 30a of each signal level detection circuit 30, 32 is obtained. , 32a to 32d are taken out to the outside and supplied to the demodulation signal selection control means 14.

In the demodulation signal selection circuit 13, the demodulation signal selection control signal 14a applied to the selection control input terminal 13c is
For example, in the case of H level, the wide band demodulated signal 11a supplied to one signal input terminal 13a is selected, and in the case of L level, the narrow band demodulated signal 35a supplied to the other signal input terminal 13b is selected. , Select output terminal 13
The signal is supplied from d to the frequency-multiplexed signal demodulation circuit 8.

The demodulation signal selection control means 14 is provided with the detection output 30a indicating that the reception signal level is equal to or higher than the preset reception signal level from the reception station signal level detection circuit 30 and the adjacent station level detection circuit 32. When none of the detection output signals 32a to 32d indicating the interference signal level from the station is output, it is determined that the electric field strength of the receiving station is strong, and the reception state is not receiving interference from the adjacent station. Then, for example, the H-level demodulation signal selection control signal 14a is output.

As described above, the FM radio receiver 1 according to the present invention is configured to automatically switch between the wideband demodulated signal 11a and the narrowband demodulated signal 35a based on the signal levels of the receiving station and the adjacent station. Therefore, when the receiving level of the receiving station (desired station) is high and the receiving state is good without interference, the wideband demodulation signal 11a which is the demodulation output of the first intermediate frequency amplification stage is automatically selected. When high-fidelity reproduction is performed and interference is generated by signals from adjacent stations, the adaptive tracking filter circuit 24 shown in FIG. 2 is used to narrow the pass band and improve the selectivity. Interference can be reduced.

FIG. 2 is a block diagram of an adaptive tracking filter FM demodulation device incorporating a first intermediate frequency signal demodulation section and a circuit section relating to demodulation signal selection. As shown in FIG. 2, by providing the first intermediate frequency signal demodulation unit 11, the demodulation signal signal selection circuit 13, and the demodulation signal selection control means 14 in the adaptive tracking filter FM demodulation device 20, the pass band The detection outputs 30a, 30b, 32a to 32d of the reception station signal level detection circuit 30 and the adjacent station signal level detection circuit 32 for control can be effectively used as input signals for demodulation signal selection.

Since the additional circuit scale is relatively small, the conventional integrated circuit for the adaptive tracking filter FM demodulator 102 is improved to create a dedicated integrated circuit for the single / double superheterodyne automatic switching system. It is also relatively easy to do.

The demodulation signal selection control means 14 may not be separately provided, but a logic circuit or the like for generating the demodulation signal selection control signal 14a may be provided in the pass band control circuit 34, or a new logic circuit section may be provided. Alternatively, when the pass band designation information 34a outputs the information designating the band A shown in FIG. 5, for example, the wide band demodulation signal may be selected.

[0044]

As described above, the FM according to the present invention
The radio receiver includes a first intermediate frequency signal demodulation unit that demodulates the first intermediate frequency signal of the first intermediate frequency amplification stage having a wide signal pass band and outputs a wideband demodulated signal, and a signal passing from the first intermediate frequency amplification stage. The second intermediate frequency signal of the second intermediate frequency amplification stage having a narrow band and a second intermediate frequency signal demodulating unit for demodulating the second intermediate frequency signal and outputting a narrow band demodulated signal are provided. Wideband demodulation signal is selected when the signal level of the receiving station is high and the signal level of the adjacent station is low based on the detection outputs of the level detection circuit and the signal level detection circuit of the adjacent station when there is no interference. With this configuration, when the reception state is good, the wideband demodulated signal is selected, and the reproduction with a wide reproduction frequency band and high fidelity can be automatically performed.

[Brief description of drawings]

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

FIG. 2 is an adaptive tracking filter FM incorporating a first intermediate frequency signal demodulation unit and a circuit unit related to demodulation signal selection.
Block diagram of demodulator

FIG. 3 is an overall block 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, 7
... intermediate frequency filter (fixed type), 7a ... first intermediate frequency output signal, 11 ... first intermediate frequency signal demodulation section, 11a ... wideband demodulation signal, 12, 20 ... adaptive tracking filter FM demodulation device, 13 ... demodulation signal Selection circuit, 14 ... Demodulation signal selection control means, 14a ... Demodulation signal selection control signal, 35
The second intermediate frequency signal demodulation unit, 35a ... Narrow band demodulation signal.

Front page continued (72) Inventor Nobuo Maeda 3-12 Moriya-cho, Kanagawa-ku, Yokohama, Kanagawa Japan Victor Company of Japan, Ltd. (72) Inventor Masanori Ianaka 111, Nishiyote-cho, Takasaki-shi, Gunma (72) Inventor Furuya Tomio 1-1 Nishiyote-cho, Takasaki-shi, Gunma

Claims (1)

Claim: What is claimed is: 1. A double superheterodyne comprising a first intermediate frequency amplification stage and a second intermediate frequency amplification stage having a signal pass band narrower than the signal pass band of the first intermediate frequency amplification stage. In the FM radio receiver of the method, a first intermediate frequency signal demodulation unit that demodulates the output signal of the first intermediate frequency amplification stage and outputs a wideband demodulated signal, and an output signal of the second intermediate frequency amplification stage is demodulated. A second intermediate frequency signal demodulation section for outputting a narrow band demodulated signal, a demodulation signal selection circuit for selecting one of these two demodulation signals, and a second intermediate frequency signal of the second intermediate frequency amplification stage. A receiving station signal level detection circuit for detecting the signal level of the receiving station based on the signal component, and a signal level of the adjacent station based on the high frequency signal component of the second intermediate frequency signal of the second intermediate frequency amplification stage. adjacent A signal level detection circuit and the wideband demodulated signal in a receiving state in which the signal level of the receiving station is higher than a preset receiving signal level and the signal level of the adjacent station is lower than a preset disturbing signal level, otherwise The FM radio receiver, further comprising demodulation signal selection control means for controlling the demodulation signal selection circuit so as to select the narrow band demodulation signal in the reception state.