JPH0553316U - FM stereo receiver - Google Patents

Abstract

(57) [Abstract] [Purpose] The input signal level of the digital stereo decoder 9 is set according to the degree of modulation to perform noise reduction and low distortion factor reproduction. / Performs stereo playback. [Configuration] A plurality of filter circuits 5 and 6 for setting the pass band of the FM demodulated signal and a switch 7 are provided, and an A / D converter 9a, a DSP 9b, a D / A converter 9c and a clock oscillator 9d are provided in the FM stereo demodulation circuit. The digital stereo decoder 9 provided therein is provided, and the VCA 8 for varying the input signal level of the digital stereo decoder 9 is provided so as to set the optimum reception condition.

Description

[Detailed description of the device]

[0001]

[Industrial application]

 The present invention relates to an FM stereo demodulation circuit of an FM stereo receiver, and more particularly to an FM stereo receiver suitable for noise reduction and low distortion reproduction of a stereo demodulation signal by a digital stereo decoder.

[0002]

[Prior art]

 Conventionally, many FM stereo receivers have the block diagram shown in FIG. In the figure, reference numeral 1 is a receiving antenna, which receives FM broadcast radio waves, receives the desired FM broadcast by electronically tuned heterodyne detection using the varicap of the FM front end 2, and receives an IF filter 3 The FM demodulation signal was output from the FM demodulation circuit 4 via.

Reference numeral 5 is a low-pass filter (hereinafter referred to as LPF). This LPF 5 is for extracting the stereo-modulated band of the FM demodulated signal and extracts a signal up to 53 kHz without waveform distortion, and a switching type multiplex circuit 20 The stereo L / Rch signal is reproduced by (hereinafter referred to as MPX20) and output from the Lch output terminal 11 and Rch output terminal 12 via the muting circuit 10.

Reference numeral 13 denotes a microcomputer (hereinafter, referred to as a microcomputer). The microcomputer 13 operates as a local oscillator for controlling the tuning frequency of the FM front end 2 to generate an intermediate frequency (IF), and further, IF By controlling the filter 3 and MPX20, L / Rch playback signals and monaural / stereo playback signals can be generated. Reference numeral 15 is a key matrix, which is connected to the microcomputer 13 to receive a user's instruction and displays various mode settings and setting values of the FM stereo receiver on the display 16 connected to the microcomputer 13.

In the FM stereo receiver thus configured, the maximum input is set to 200% modulation level or higher in consideration of overmodulation of the FM broadcasting station, and distortion due to overmodulation is prevented. Furthermore, in order to reduce noise during FM stereo demodulation due to interference of adjacent stations and radio interference due to multiple FM broadcasting stations, the pass band of IF filter 3 is narrowed by the control of microcomputer 13, or FM stereo demodulation is performed. After that, the high frequency components of the Lch signal and the Rch signal were mixed to make the noise inconspicuous and stereo reproduction was performed.

When the reception condition of FM broadcasting is bad, FM stereo demodulation is stopped and monaural demodulation is performed, and the same signal is output to the L / Rch output terminals 11 and 12 via the analog LPF of the MPX circuit 20. Was there.

[0007]

[Problems to be solved by the device]

 However, in the conventional FM stereo receiver described above, the input of the MPX circuit 20 was set to full scale at 200% input level in order to prevent distortion due to overmodulation. However, the S / N and distortion ratios were worse than when full scale input was used.

Further, in order to reduce noise during FM stereo demodulation due to interference from adjacent stations or radio interference, the pass band of the IF filter 3 was narrowed and the high frequency components of L / Rch were mixed. There is a drawback that the separation at high frequencies is deteriorated.

Furthermore, when the reception condition of the FM broadcast is bad, the same signal is output to the L / Rch by the analog LPF of the MPX circuit 20 for monaural reproduction, so the frequency characteristics of the output signal are those of the analog LPF above. There was also the drawback that the output frequency characteristics could not be changed because it was decided.

The present invention has been made in view of the above points, and an object thereof is to solve the drawbacks of the conventional example, use a digital stereo decoder in an FM stereo demodulation circuit, and input signal level of the digital stereo decoder. This is to provide an FM stereo receiver that can perform noise reduction and low-distortion rate reproduction by changing the frequency, and can switch between multiple filter circuits to perform monaural / stereo reproduction.

[0011]

[Means for Solving the Problems]

 The FM stereo receiver of the present invention is equipped with a voltage control amplifier (hereinafter, referred to as VCA) for varying the input signal level at the input side of a digital stereo decoder having an A / D converter, and the signal processing level of the above digital stereo decoder. Is configured to be controlled by the above VCA according to the FM broadcast received signal.

Further, an A / D converter that converts an analog signal of the FM stereo demodulated signal into a digital signal and performs sampling, and a clock oscillator that generates a clock signal that processes the signal in synchronization with the pilot signal of the FM stereo signal , Equipped with a digital signal processor (hereinafter referred to as DSP) that performs oversampling filter operation on digital data of FM stereo signals, and a D / A converter that converts the output data of this DSP to analog signals and performs de-emphasis processing. It may be configured with a digital stereo decoder.

Further, a plurality of filter circuits provided between the FM demodulation circuit and the VCA and a switcher for switching and setting the plurality of filter circuits are provided to set the FM demodulation signal of the FM stereo broadcast to the above setting. The filter may be configured to reduce adjacent station noise.

Further, a microcomputer for controlling the DSP, VCA, a plurality of filter circuits, and a switch, and a memory built in the microcomputer for storing reception stereo reproduction conditions of a plurality of receivable FM broadcasting stations. You may.

[0015]

[Action]

 According to this invention, a stereo demodulation circuit is provided with a digital stereo decoder for stereo reproduction, and this digital stereo decoder is an A / D converter that converts an analog signal of an FM stereo demodulation signal into a digital signal and performs sampling. , A clock oscillator that generates a clock signal that performs signal processing in synchronization with the pilot signal of the FM stereo signal, a DSP that performs an oversampling filter operation on the digital data of the FM stereo signal, and the output data of this DSP is converted to an analog signal. And a D / A converter that performs de-emphasis processing, and can output a stereo playback signal from the L / Rch output terminals.

A VCA for varying the input signal level of the digital stereo decoder is provided, and the signal processing level of the digital stereo decoder is controlled by the VCA according to the modulation degree of the FM transmission / reception signal, and the operation level of the A / D converter is changed. By operating at almost 100% full scale level at all times, noise and S / N deterioration due to overmodulation of FM broadcasting can be reduced, and low distortion stereo playback can be performed.

Further, a plurality of low-pass filter (hereinafter referred to as LPF) circuits provided between the output of the FM demodulation circuit and the input of the VCA are provided, and the plurality of LPF circuits are switched and set by a switching device, Control is performed so that only the main channel signal (including pilot signal) of FM stereo demodulation is extracted and monaural reproduction is performed to prevent frequency interference and radio interference from adjacent stations in FM stereo broadcasting, and reduce noise from adjacent stations. It is possible to perform good S / N stereo reproduction with low distortion.

Further, a microcomputer setting program for controlling settings of the above DSP oversampling filter calculation, setting of VCA input signal level, and setting of switching of a plurality of LPF circuits by a switcher is stored in a built-in memory. can do.

That is, when the desired FM broadcast station is received by storing the reception stereo reproduction conditions of a plurality of FM broadcast stations that can be received by the FM stereo receiver, the reception of the optimum stereo reproduction stored in the memory is performed. By automatically calling and setting the conditions, the user can always receive the FM broadcast under the optimum conditions.

[0020]

【Example】

 An embodiment of the FM stereo receiver according to the present invention will be described based on the block diagram of FIG. The same parts as those of the conventional example are designated by the same reference numerals and the description thereof will be omitted. In the figure, 5 is the first low-pass filter (first LPF) up to 53kHz for extracting the FM stereo signal, and 6 is, for example, the main channel signal and pilot signal of the L + R component in the FM stereo modulated band. It is a second LPF for extracting a signal up to (19 KHz), and the first and second LPFs 5 and 6 are switched and controlled by the switch 7.

Reference numeral 8 denotes a voltage control amplifier (VCA) controlled to an amplification gain designated by the microcomputer 13, and an FM stereo demodulation output signal whose level is set by this VCA 8 is supplied to a digital stereo decoder 9.

The digital stereo decoder 9 is composed of an A / D converter 9a, a DSP 9b, a D / A converter 9c and a clock oscillator 9d. The A / D converter 9a outputs an output signal to a predetermined signal according to a timing signal from the clock oscillator 9d. It is sampled at the position, converted to digital data and supplied to the DSP9b. The DSP9b performs oversampling filter operation on the supplied digital data using the instruction command and operation data instructed by the microcomputer 13, and converts it to L / Rch analog signal by the D / A converter 9c. Furthermore, it passes through the built-in LPF that attenuates unnecessary band by de-emphasis processing and outputs.

The clock oscillator 9d generates a clock signal necessary for the A / D converter 9a, the DSP 9b and the D / A converter 9c by a clock synchronized with the pilot signal in the VCA8 output signal and supplies the clock signal to each circuit. To do. If there is no instruction from the microcomputer 13 or if no pilot signal is detected, the clock oscillator 9d generates a predetermined clock signal and supplies it to each circuit.

As is well known, the microcomputer 13 basically comprises a CPU, a ROM, a RAM, an input port and an output port. By setting the tuning frequency of the FM front end 2 to the frequency division ratio of the program divider. Control, control the pass frequency bandwidth of the IF filter 3, control the selective switching of the switcher 7, control the gain of the VCA 8 and set the output voltage level, and set the A / D converter 9a of the digital stereo decoder 9 full. It controls the scale input and supplies a muting control signal to the muting circuit 10.

On the other hand, the microcomputer 13 controls the DSP 9b by supplying the arithmetic operation command command and the arithmetic coefficient data to perform a predetermined filtering operation, receiving the lock detection signal for the pilot signal of the clock oscillator 9d, and receiving the digital stereo decoder. 9 determines whether or not FM stereo demodulation is being performed, and selectively controls the switch 7 to determine the selection side of the first and second L PF5,6 and also to cause the DSP 9b to perform FM stereo demodulation operation. Instruct whether or not.

Reference numeral 14 is a data ROM, and this data ROM 14 is accessed by the microcomputer 13 so as to store the arithmetic operation command instruction and the arithmetic coefficient data for the operation of the DSP 9b. Reference numeral 15 is a key matrix, and user instructions can be given from the key matrix 15 to the microcomputer 13. 16 is a reception frequency, a pass frequency bandwidth of the IF filter 3, a monaural / stereo setting of FM stereo, and A / This is a display that displays the over-flow of the D converter 9a and the setting of the low-pass filter of the DSP 9b using the microcomputer 13.

The FM stereo receiver configured in this manner cuts unnecessary frequency bands of the received FM stereo signal with the IF filter 3 during FM stereo reproduction, and outputs the FM stereo output signal of the first LPF 5 via the switch 7. Supplied to VCA8. The gain of the VCA8 supplied with the FM stereo signal is adjusted according to the modulation degree of the FM broadcasting station of the FM stereo signal. That is, the user operates the key matrix 15 to give an instruction to the microcomputer 13, and set the gain of the VCA 8 so that the full scale display of the A / D converter 9a displayed on the display 16 connected to the microcomputer 13 is displayed. The microcomputer 13 can store the FM stereo signal level corresponding to the modulation degree of the receiving FM broadcasting station.

In this way, the input level of the A / D converter 9a of the digital stereo decoder 9 is set according to the modulation degree of the receiving FM broadcasting station, and the S / N of the digital stereo decoder 9 and the input signal with a good distortion rate are set. Can be set to level range. This set value can be stored in the built-in memory for each FM broadcasting station that can receive it.

Further, since the output frequency band of the digital stereo decoder 9 is determined by the calculation of the DSP 9b, the microcomputer 13 calls the calculation specification pre-stored in the data ROM 14 by the user's instruction from the key matrix 15 and the calculation operation of the DSP 9b. The specifications can be set, and the output frequency band of the digital stereo decoder 9 can be set corresponding to each of the receivable FM broadcasting stations.

Further, when the user operates the key matrix 15 to set the FM stereo broadcast to the monaural reproduction output, the microcomputer 13 controls the switch 7 to extract the FM stereo signal up to the pilot signal. The output signal is supplied to the VCA 8 and the clock oscillator 9d of the digital stereo decoder 9 is controlled to oscillate with a predetermined clock, and the digital stereo decoder 9 is operated by this clock to operate the Lch and Dch of the D / A converter 9c. The same output signal is obtained for the Rch output, and the monaural reproduction signal is output to the L / Rch output terminals 11 and 12.

As described above, the input signal level setting during the stereo reproduction and the setting function during the monaural reproduction are combined with the frequency bandwidth control of the IF filter 3 corresponding to the receiving FM broadcasting station and the gain control of the VCA8. , DSP9b calculation specifications, monaural / stereo playback setting control, etc. are stored in the microcomputer 13 to call out the desired FM broadcast station from among the receivable FM broadcast stations, and at the same time call the stored receive setting function. It is possible to automatically set each setting of the FM stereo receiver to the optimum reception corresponding to the reception of the FM broadcasting station.

Further, for example, a 3-contact switching device is used as the switching device 7, the AM detection output is input to the remaining 1 contact of the specifications, and when the AM broadcast reception input is selected, the AM reception is supported. The VCA 8 gain setting, the DSP 9b calculation specifications and the clock oscillator 9d predetermined clock oscillation operation settings are controlled by the microcomputer 13, and each circuit is set by the stored data that is stored. It is also possible to have.

Further, the same effect can be obtained by using the program attenuator controlled by the microcomputer 13 for the VCA 8 and controlling the attenuator so that the amplification gain is set by the receiving broadcasting station in the same manner as described above.

[0034]

[Effect of the device]

 As described above, the FM stereo receiver according to the present invention corresponds to each receivable broadcasting station by setting the input signal level of the digital stereo decoder and the setting of monaural / stereo reproduction, etc. Since it can be set together with the setting, the effect is that the reception of the desired broadcasting station can be automatically received under the optimum reception conditions.

Further, since various reception setting conditions can be stored in the internal memory corresponding to a plurality of receivable broadcasting stations, FM stereo reception can be easily performed by simply calling the memory to the desired receiving broadcasting station. There is also an effect that the reception condition of the machine can be set.

Moreover, since the structure is simple, the cost can be reduced, and the function can be improved largely depending on the software controlled by the microcomputer, the excellent features such as easy implementation can be obtained. Have

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an FM stereo receiver of the present invention.

FIG. 2 is a block diagram showing a conventional example.

[Explanation of symbols]

 1 Reception Antenna 2 FM Front End 3 IF Filter 4 FM Demodulation Circuit 5 First Low Pass Filter (LPF) 6 Second Low Pass Filter (LPF) 7 Switcher 8 Voltage Controlled Amplifier (VCA) 9 Digital Stereo Decoder 9a A / D Converter 9b Digital signal processor (DSP) 9c D / A converter 9d Clock oscillator 10 Muting circuit 11 Lch output terminal 12 Rch output terminal 13 Microcomputer 14 Data ROM 15 Key matrix 16 Display

Claims (4)

[Scope of utility model registration request] 1. A digital stereo decoder having an A / D converter is provided with a voltage control amplifier for varying an input signal level on an input side thereof, and a signal processing level of the digital stereo decoder is controlled according to an FM broadcast reception signal. An FM stereo receiver characterized by being configured to be controlled by an amplifier. 2. An A / D converter for converting an analog signal of FM stereo demodulation into a digital signal for sampling, a clock oscillator for generating a clock for signal processing in synchronization with a pilot signal of the FM stereo signal, and an FM stereo signal. A digital stereo decoder configured to perform an oversampling filter arithmetic operation on the digital data of the above, and a D / A converter for converting the output data of the digital signal processor into an analog signal to perform de-emphasis processing. And FM stereo receiver. 3. A plurality of filter circuits provided between the FM demodulation circuit and the voltage control amplifier, and a switcher for switching and setting the plurality of filter circuits are provided, and the FM demodulated signal of FM stereo broadcasting is provided as described above. The FM stereo receiver according to claim 1 or 2, wherein the setting stereo filter reduces adjacent station noise. 4. A microcomputer for controlling the digital signal processor, a voltage control amplifier, a plurality of filter circuits and a switch, and a reception stereo reproduction condition of a plurality of receivable FM broadcasting stations in a memory built in the microcomputer. The FM stereo receiver according to claim 1, 2 or 3, characterized in that the FM stereo receiver is stored.