JPS58201434A - Fm receiver - Google Patents

Abstract

PURPOSE:To perform FM reception with good sense of listening, by performing the detection of a distorted component from an AGC signal of an intermediate frequency amplifier section and controlling the degree of stereophonic separation and the tone of a detecting circuit. CONSTITUTION:The AGC signal obtained from a terminal (d) of the intermediate frequency amplifier section 3 of an FM receiving section 8 is applied to an amplifier circuit 15 via an LPF17 and an HPF. When the FM receiving section 8 is subjected to multipath and a voltage standing wave, the AGC signal is fluctuated by them, the distorted component is applied to the amplifier circuit 15. This component of distortion is applied to an automatic stereophonic separation controlling and driving circuit 12 and an automatic tone adjustment controlling and driving circuit 13 via an amplifier circuit 17' and a detecting circuit 16. These circuits 12, 13 decrease the degree of stereophonic separation at an FM stereophonic demodulating section 5 depending on the amplitude of the component of distortion and decreases the tone. In this case, the restoration of the degree of stereophonic separation and the tone when the distortion signal is lost is controlled so as to be done gradually.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an output signal (hereinafter referred to as AG
The F signal is designed to detect voltage fluctuations caused by multipath and electric field standing waves in the C signal, control the stereo separation degree and tone (sound quality) of the stereo demodulation circuit, and improve the audibility.
M receiver.

An example of an FM receiver having a conventional automatic stereo separation control (hereinafter referred to as ASC) device and automatic tone control (hereinafter referred to as ATC) device is shown in FIG. To explain this, 1 is an antenna for FM reception, 2 is a cheese section of the FM reception section 8, 3 is an intermediate frequency amplification section, 4 is an FM detection section, 6 is an FM stereo demodulation section, and 6 is a power amplification section. , 7 is a speaker, which receives the output signal of the power amplification section 6 and generates sound. a is a demodulation output terminal for extracting the FM detection output signal, b is an ASC drive voltage input terminal that supplies the DC voltage necessary for ASC operation, and C supplies the DC voltage necessary for ATC operation. The ATC drive voltage input terminal 9 is a band pass filter that only passes the 19 KHz FM pilot signal from the demodulated signal.
The 19 KHz FM pilot signal extracted here enters the detection circuit 10 and is converted into a positive DC voltage corresponding to the level of fluctuation due to distortion. Reference numeral 11 denotes a DC amplifier circuit, which amplifies the output DC voltage of the detection circuit 10 to a voltage at which the 9th-order ASC drive circuit 12 and ATC drive circuit 13 can sufficiently operate. The ASC drive circuit 12 outputs a DC voltage for controlling the degree of stereo separation according to distortion variations, and is applied to the ASC drive voltage input terminal of the FM receiver 80 and the FM stereo demodulator 5. Also, ATC
, the drive circuit 13 outputs a DC voltage for controlling the tone according to distortion variations, and is applied to the ATC drive drive voltage input terminal of the FM stereo demodulator 6 of the FM receiver 8.

In the FM stereo demodulation 6, the ASC circuit and the ATC circuit change the degree of stereo separation and tone using a DC voltage corresponding to the variation of the distortion component added to the ASC drive voltage input terminal and the ATC drive voltage input terminal. The audio signal whose stereo separation degree and tone have been changed is amplified by a power amplification section 6 and outputted by a speaker 7.

However, this conventional example detects fluctuations in the distortion components of the 19KH2 FM pilot signal.

If there is a slight tuning shift in the FM receiver, this 19K
Normal ASC drive voltage and ATC drive voltage cannot be obtained because there is a difference in the amount of variation in the distortion component of the Hz FM pilot signal. In addition, instantaneous overmodulation can reduce fluctuations by 19K, similar to fluctuations in distortion components due to multipath and voltage standing waves.
Since an FM pilot signal of Hz is received, the ASC circuit and ATC circuit operate in response to this instantaneous overmodulation. Furthermore, in the conventional example, when distortion increases, the ASC circuit and ATC circuit operate to lower the degree of stereo separation, lowering the tone and improving the audibility, but when distortion suddenly decreases, the degree of stereo separation increases at the same time. , the tone rises. When multipath or electric field standing waves occur sporadically, changes in stereo separation and tone also occur sporadically, which has the disadvantage of giving an audible sense of discomfort.

The present invention is designed to eliminate such drawbacks of the conventional example. Hereinafter, the present invention will be explained based on illustrated embodiments. FIG. 2 shows a block configuration diagram of an embodiment of the present invention. Blocks 1 to 8 in the figure operate in the same way as those explained in FIG. is omitted. In FIG. 2, d is an AGC signal output terminal that is output from the intermediate frequency amplification section 3 according to the electric field strength, and a positive DC voltage is output. When the FM receiver 8 receives multipath or voltage standing waves, the voltage value of the AGC signal also changes accordingly. Therefore, by detecting this fluctuation component, the degree of stereo separation and tone can be changed. In order to detect fluctuations in distortion components, the cutoff frequency 2
The signal is passed through a 0KHz low-pass filter 17 to remove unnecessary external noise. The signal after passing through the low-pass filter 17 is:

A bypass filter 14 allows only signals of IKHz or higher to pass through. This is compared to the voltage standing wave skip noise of up to 30 Hz.

This is because distortion components due to multipath are distributed in the frequency range of 20 Hz or higher, so by extracting signals of 100 Hz or higher, skip noise can be removed, and if the cutoff frequency of the bypass filter is set to about IKHz, the distortion components can be sufficiently removed. This is because it is possible to detect only The extracted signal is amplified by the AC amplifier circuit 16 so that it falls within the normal operating range of the detection circuit 16. Thereafter, the detector circuit 16 converts the distortion component into a DC voltage according to the amount of variation in the distortion component, and the DC amplifier circuit 11 converts the voltage into the ASC drive circuit 12 and the ATC drive circuit 1.
3 is amplified to operate in a sufficiently stable region. A
The SC control voltage is output from f, and the ATC control voltage is output from q. Below, 12, 13, b, c.

6.6.7 operates in the same way as shown in FIG. 1, so the explanation here will be omitted.

FIG. 3 is a wiring diagram of a specific embodiment of the present invention. This will be explained below. e is an AGC signal input terminal, and the AGC signal input here enters a low-pass filter 17 made up of a resistor 49 and a capacitor 60. In this embodiment, the cutoff frequency is 20 KHz. The signal after passing through the low-pass filter 17 is sent to the operational amplifier 5.
1 and enters the I-pass filter 14.

This cutoff frequency was set to 3 KHz in this example. The output signal of the no-pass filter 14 enters the detection circuit 16 after being amplified by the AC amplifier circuit 16 to ensure sufficiently stable operation of the detection circuit 16. The signal half-wave rectified by diode 28 passes through buffer 30 and enters the anode of diode 31. The cathode of the diode 31 is grounded through a resistor 32 and a capacitor 33 connected in parallel. When a change in the distortion component is detected and a signal is applied to the diode 31, the signal is applied to the capacitor 33 via the diode 31.
is charged, and its charging time constant is small. However, when the distortion component suddenly disappears, the potential on the cathode side of the diode 31 becomes high and reverse bias is applied, increasing its impedance. Therefore, the charge stored in the capacitor 33 is discharged via the resistor 32, and the discharge time constant is larger than the charging time constant. In other words, when a change in the distortion component is detected.

The detection circuit 16 outputs a DC voltage according to the fluctuation, but is configured to gradually lower the output voltage when the distortion component disappears. The output voltage of the detection circuit 16 is amplified by the DC amplifier 11 so that the operational amplifiers 43 and 44 of the ASC drive circuit 12 and the ATC drive circuit 13 operate within the allowable input range. Operational amplifier 43
operates in the allowable input region, the desired ASC drive voltage cannot be obtained, so transistor 45 and resistor 4
The desired ASC drive voltage is obtained by the emitter follower circuit No. 7. Similarly, the emitter follower circuit of the transistor 46 and the resistor 48 is used to obtain a desired ATC drive voltage. The ASC drive voltage is output from terminal f, and AT
The C drive voltage is output from terminal q.

As is clear from the above description, in the present invention, since the distortion component is detected from the AGC signal of the intermediate frequency amplification section, fluctuations due to tuning deviation are smaller than in the conventional example.

Furthermore, fluctuations in distortion components due to instantaneous overmodulation are also smaller than in the conventional example. In addition, when the distortion component disappears in the detection circuit, by gradually lowering its output voltage, the degree of stereo separation gradually increases, and the tone also gradually increases, eliminating any audible discomfort. , it is possible to obtain the effect that better reception can be achieved than in the conventional example. 9 more
When the present invention is used in conjunction with diper/Tee reception, the sudden change in the AGC signal to i when switching antennas is eliminated by a low-pass filter.

Another advantage is that good reception can be achieved without any malfunction or audible discomfort.

In this way, the present invention detects the distortion component from the AGO signal of the intermediate frequency amplification section, and by configuring the detection circuit with a small charging time constant and a thick discharging time constant, the degree of stereo separation and tone are improved. This makes it possible to realize an FM receiver that can control FM without any audible discomfort.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional FM receiver, FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 3 is a circuit diagram of a specific embodiment of the present invention. 2... Cheating section, 3... Intermediate frequency amplification section, 4... FM detection section, 6... S stereo demodulation section, 8...・FM receiving section, 11...
DC amplifier circuit, 12...ASC drive circuit, 13
...ATC drive circuit, 14...Bypass filter, 16...AC amplifier circuit, 16...
...Detection circuit, 17...Low-pass filter,
b...ASC drive voltage input terminal, C...
・ATC drive voltage input terminal, d...AGC signal output terminal.

Claims (1)

[Claims] Using the output signal obtained from the automatic gain control output terminal that can extract an output according to the reception level from the intermediate frequency amplification section of the FM reception section, distortion caused by multipath and electric field standing waves can be suppressed. Detect variations in components. It includes a distortion component variation detection circuit, an automatic stereo separation degree control drive circuit, and an automatic tone control drive circuit for controlling the stereo separation degree and tone, and the output signal from the automatic gain control signal output terminal is The automatic stereo separation degree driving circuit and the automatic tone control driving circuit are connected so that the stereo separation degree and tone can be controlled by a DC voltage input to the detection circuit and according to the output signal of the detection circuit, and fluctuations in distortion components are suppressed. When detected, the FM receiver lowers the degree of stereo separation and lowers the tone, and even when the distortion component disappears, the degree of stereo separation is gradually increased and control is performed so as to raise the tone.