JPS639781B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an output signal from an automatic gain control (AGC) signal output terminal (hereinafter referred to as AGC This product provides an FM receiver that detects voltage fluctuations caused by multipath and electric field standing waves (referred to as signals) and controls the stereo separation degree and tone (sound quality) of a stereo demodulation circuit to improve hearing sensation. It is.

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 tuner section of the FM reception section 8, 3 is an intermediate frequency amplification section, 4 is an FM detection section, 5 is an FM stereo demodulation section, 6 is a power amplification section, 7 is a speaker,
The output signal of the power amplifying section 6 is input to generate 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,
c is an ATC drive voltage input terminal that supplies the DC voltage necessary for ATC operation, and 9 is a bandpass filter for passing only the 19KHz FM pilot signal from the demodulated signal. FM pilot signal is detected by detection circuit 1
0 and is exchanged to a positive DC voltage according to the level of fluctuation due to distortion. 11 is a DC amplifier circuit;
This changes the output DC voltage of the detection circuit 10 to
The voltage is amplified to a voltage that allows the ASC drive circuit 12 and ATC drive circuit 13 to operate sufficiently. The ASC drive circuit 12 outputs a DC voltage for controlling the degree of stereo separation according to variations in distortion, and is applied to the ASC drive voltage input terminal b of the FM stereo demodulator 5. Further, the ATC drive circuit 13 outputs a DC voltage for controlling the tone according to distortion fluctuations, and the FM stereo demodulator 5 of the FM receiver 8
Applied to ATC drive voltage input terminal c. In the FM stereo demodulator 5, the ASC circuit and the ATC are controlled by the DC voltage corresponding to the fluctuation of the distortion component applied to the ASC drive voltage input terminal b and the ATC drive voltage input terminal c.
The circuit changes the degree of stereo separation and tone. 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, since this conventional example detects fluctuations in the distortion component of the 19KHz FM pilot signal,
If the FM receiver is slightly out of tune, this
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 19KHz FM pilot signal. In addition, even with instantaneous overmodulation, the 19KHz FM pilot signal receives fluctuations similar to fluctuations in distortion components due to multipath and voltage standing waves, so the ASC circuit
ATC circuit operates. 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 creating 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 of an AGC signal outputted from the intermediate frequency amplifying section 3 according to the electric field strength, and a positive DC voltage is outputted.
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 signal is passed through a low-pass filter 17 with a cutoff frequency of 20 KHz to remove unnecessary external noise. After passing through the low pass filter 17, the signal is passed through the high pass filter 14 at 1KHz.
Only the above signals are allowed to pass. This is because while the skip noise of voltage standing waves is up to 30Hz at most, the distortion components due to multipath are distributed in the frequency range of 20Hz or higher.By extracting the signal of 100Hz or higher, the skip noise can be reduced. excluded,
This is because if the cutoff frequency of the high-pass filter is set to about 1 KHz, only the distortion component can be detected sufficiently.
The extracted signal is amplified by the AC amplifier circuit 15 so that it falls within the normal operating range of the detection circuit 16. Thereafter, the detection circuit 16 converts it into a DC voltage that increases as the distortion component increases and gradually decreases when the distortion component decreases,
Then, the signal is amplified so that the ASC drive circuit 12 and the ATC drive circuit 13 operate in a sufficiently stable region.
The ASC control voltage is output from f, and the ATC control voltage is output from g. Below, 12, 13, b, c, 5,
6 and 7 operate in the same way as shown in FIG. 1, so their 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 consisting of a resistor 49 and a capacitor 50. In this embodiment, the cutoff frequency is 20KHz. The signal after passing through the low-pass filter 17 is amplified by the operational amplifier 51 and enters the high-pass filter 14. This cutoff frequency was set to 3KHz in this example. The output signal of the high-pass filter 14 is input to the detection circuit 16 after being amplified by the AC amplifier circuit 15 in order to make the detection circuit 16 operate in a sufficiently stable manner. diode 28
The half-wave rectified signal passes through a buffer 30 and enters the anode of a diode 31. The cathode of the diode 31 is connected to a resistor 32 and a capacitor 33.
grounded through a parallel connection. When a change in the distortion component is detected and a signal is applied to the diode 31,
Capacitor 33 is charged via diode 31, 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, capacitor 3
3 is discharged via the resistor 32, and the discharge time constant is larger than the charging time constant. That is, when a fluctuation in the distortion component is detected, the detection circuit 16 outputs a DC voltage corresponding to the fluctuation, but when the distortion component disappears, the output voltage is gradually lowered. The output voltage of this detection circuit 16 is the same as that of the ASC drive circuit 12 and the ATC
Operational amplifier 43 and operational amplifier 44 of drive circuit 13
is amplified by a DC amplifier 11 so that it operates within an allowable input range. When the operational amplifier 43 operates in the permissible input region, the desired ASC drive voltage cannot be obtained, so the transistor 45 and the resistor 4
The desired ASC drive voltage is obtained by the emitter follower circuit No.7. Transistor 46 and resistor 48
Similarly, the emitsuta follower circuit of
This is to obtain the ATC drive voltage. ASC drive voltage is output from terminal f, ATC drive voltage is output from terminal g
It is output from

As is clear from the above description, since the present invention detects the distortion component 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. Also,
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. Furthermore, when the present invention is used in conjunction with diversity reception, rapid changes in the AGC signal when switching antennas are filtered out by the low-pass filter, allowing for good reception without any malfunction or audible discomfort. Effects can also be obtained.

In this way, the present invention can improve the AGC of the intermediate frequency amplification section.
By detecting distortion components from the signal and configuring the detection circuit with a small charging time constant and a large discharging time constant, it is possible to realize an FM receiver that can control stereo separation and tone without causing any audible discomfort. It is something.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional FM receiver, Figure 2 is a block diagram of a conventional FM receiver.
The figure is a block diagram of one embodiment of the invention, and FIG. 3 is a circuit diagram of a specific embodiment of the invention. 2... Tuner section, 3... Intermediate frequency amplification section, 4
...FM detection section, 5...Stereo demodulation section, 8...
FM receiving section, 11... DC amplifier circuit, 12...
ASC drive circuit, 13...ATC drive circuit, 14...
...High pass filter, 15...AC amplifier circuit, 1
6...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] 1 Detects fluctuations in distortion components due to multipath and electric field standing waves using the output signal obtained from the automatic gain control output terminal, which can extract output according to the reception level from the intermediate frequency amplification section of the FM receiver section. an automatic stereo separation degree control drive circuit and an automatic tone control drive circuit for controlling stereo separation degree and tone; An FM receiver characterized in that the DC voltage generated by being input to the detection circuit having different rectifier circuits is input to the automatic stereo separation degree drive circuit and the automatic tone control drive circuit.