JPH01231441A - Fm stereo receiver - Google Patents

Abstract

PURPOSE:To obtain excellent separation by supplying directly an output signal of a FM detection means to a pulse noise detection system, using a separation compensation means so as to compensate an output signal of the FM detection means and supplying the result to a stereo demodulation means. CONSTITUTION:A detection signal outputted from a FM detection circuit 1 is retarded by a delay circuit 3 and fed to a separation compensating circuit 13. The separation compensating circuit 13 increases the level of a high frequency component of a detection signal retarded in response to the resistance of a variable resistor 15. On the other hand, since a detection signal is supplied directly to a pulse noise detection system comprising an HPF 7, a noise amplifier 8, a noise detecting circuit 9, a waveform shaping circuit 10, a rectifier circuit 11 and an LPF 12 from the FM detecting circuit 1, the effect of the high frequency component level increase by the separation compensating circuit 13 onto the pulse noise detection is prevented. Thus, excellent separation characteristic is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an FM stereo receiver equipped with a pulse noise canceling device.

BACKGROUND ART A conventional example of an FM stereo receiver equipped with a pulse noise removing device is shown in FIG. In this receiver, a detection signal output from an FM detection circuit 1 is supplied via a separation compensation circuit 2 to a delay circuit 3 consisting of an LPF (low pass filter) and is delayed, and this delayed output is sent to a gate circuit 4 and The signal is supplied to a stereo demodulation circuit 6 via a level hold circuit 5. The detected signal is also supplied to a HPF (bypass filter) 7 for noise detection, and the noise component signal that has passed through the HPF 7 is amplified by a noise amplifier 8 and supplied to a noise detection circuit 9.

The noise detection circuit 9 includes a rectification circuit that rectifies the output signal of the noise amplifier 8 and a level determination circuit that determines the output level of the rectification circuit, and this noise detection output is supplied to the waveform shaping circuit 10. The waveform shaping circuit 10 is composed of, for example, a one-shot multi-by-break, and converts the noise detection output into a pulse having a predetermined wave height and time width, and supplies the pulse to the gate circuit 4. The gate circuit 4 is driven by the pulses supplied to the gate circuit 4 from the waveform shaping circuit 10 and enters the signal cutoff state, and in the signal cutoff state, the delayed output level immediately before the signal cutoff is held by the level hold circuit 5, and the stereo demodulation circuit is activated. 6. This prevents the occurrence of spikes due to sudden changes in potential. Further, the output signal of the noise amplifier 8 is rectified by the rectifier circuit 11 and
It is supplied to a PF (low pass filter) 12. LPF
12 forms an AGC loop by smoothing the rectified output to obtain a DC signal corresponding to the noise level and feeding it back to the noise amplifier 8.

For example, when receiving a weak electric field, white noise peculiar to FM tends to increase, and at this time, the noise level of the output signal of the HPF 7 increases. L due to increase in noise level
The DC signal level output from the PF 12 increases, and this lowers the gain of the noise amplifier 8 as an AGC signal. Therefore, the noise level supplied from the noise amplifier 8 to the noise detection circuit 9 is held constant. Due to this effect, the noise amplifier 8. Each circuit such as the noise detection circuit 9 is prevented from becoming saturated.

Note that the delay circuit 3 is provided to compensate for the time required from when the pulse noise is supplied to the HPF 7 to when the gate circuit 4 is cut off.

In such a conventional FM stereo receiver, FM
The DC signal obtained by rectifying and smoothing the high frequency component of the detection output is FM.
The pulse noise is removed by setting the average level of the high-frequency components of the detection output as the average level, detecting a signal larger than the average level as pulse noise, and controlling the gate circuit to cut off the signal.

By the way, due to the influence of the frequency characteristics of the ceramic filter in the IF amplifier circuit (not shown), the high frequency components of the detected signal are attenuated, causing a phase lag. On the other hand, in the stereo demodulation circuit 6, a stereo demodulated signal with good separation cannot be obtained unless the signal level and phase match. Therefore, the output signal of the FM detection circuit 1 is compensated by the separation compensation circuit 2. The separation compensation circuit 2 normally includes a resistor 21 as shown in FIG.
, a capacitor 22 and a variable resistor 23. However, insertion of such an HPF causes an insertion loss, and the high frequency component level, that is, the noise component level becomes larger than the other band component levels, which has a negative effect on the pulse noise detection sensitivity. Ta.

In addition, the delay circuit 3 can be used without separately providing a separation circuit.
Some have a separation adjustment function inside. For example, such a delay circuit is composed of four stages of LPFs 24 to 27 made up of resistors and capacitors, and buffer amplifiers 28 and 29 provided at their input and output, respectively, as shown in figure f87. A circuit that uses a variable resistor to adjust separation is known. However, since the delay characteristics change by adjusting the separation, there is a possibility that the pulse noise removal timing is adversely affected and the pulse noise removal becomes incomplete.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an FM stereo receiver that can obtain good separation characteristics without adversely affecting the pulse noise removal operation.

In the FM stereo receiver of the present invention, the received signal is
FM detection means for performing M detection, noise detection means for detecting pulse noise contained in the output signal of the FM detection means and generating a cutoff signal, and separation compensation means for compensating for separation of the output signal of the FM detection means. , comprising a suppression means for performing pulse noise suppression processing on the output signal of the separation compensation means in response to the cutoff signal and outputting the processed signal, and a stereo demodulation means for stereo demodulating the output signal of the suppression means. It is characterized by

Embodiments Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 4.

In the FM stereo receiver equipped with a pulse noise canceling device according to an embodiment of the present invention shown in FIG. 1, the same parts as those in the conventional device shown in FIG. A separation compensation circuit 13 is provided between the circuit 3 and the gate circuit 4, and the output signal of the FM detection circuit 1 is directly supplied to the delay circuit 3 and the HPF 7.

The separation compensation circuit 13 includes an operational amplifier 14, a variable resistor 15, a resistor 16, and a capacitor 17, as shown in FIG. A non-inverting input of the operational amplifier 14 is connected to the output of the delay circuit 3, and a variable resistor 15 is connected between the output and the inverting input of the operational amplifier 14. Further, a series circuit of a resistor 16 and a capacitor 17 is connected between the inverting input of the operational amplifier 14 and the ground. The rest of the configuration is the same as the configuration shown in FIG.

Note that the output of the separation compensation circuit 13, that is, the output of the operational amplifier 14, is connected to the gate circuit 4 and also to the PLL circuit 6a of the stereo demodulation circuit 6. The PLL circuit 6a obtains a pilot signal from the output signal of the separation compensation circuit 13 and generates a subcarrier signal of 381 kHz. This subcarrier signal and the output signal of the level hold circuit 5 are multiplied by multipliers 6b and 6c, respectively, and the output signal of the level hold circuit 5 is added to each output signal of the multipliers 6b and 6c by adders 6d and 6e. The left channel signal is sent from the adder 6d to the adder 6d.
The right channel signal is obtained from e.

In this configuration, the detection signal output from the FM detection circuit 1 is delayed by the delay circuit 3 and supplied to the separation compensation circuit 13. Separation compensation circuit 1
3 raises the level of the high frequency component of the delayed detection signal according to the resistance value of the variable resistor 15. As a result, the high frequency components of the detected signal are attenuated and the phase delay caused is compensated by an apparent increase in the upper level. The detected signal compensated in this way is sent to the PLL circuit 6a, through the gate circuit 4, the level hold circuit 5, the multipliers 6b, 6c, and the adder 6.
d and 6e, respectively, and the left and right channel signals are demodulated.

On the other hand, HPF7. Noise amplifier 8. Noise detection circuit 9
．． Waveform shaping circuit 10. Since the detection signal is directly supplied from the FM detection circuit 1 to the pulse noise detection system consisting of the rectifier circuit 11 and the LPF 12, the separation compensation circuit 13
This prevents the increase in the level of high-frequency components due to this from affecting the pulse noise detection operation.

3 and 4 show other circuit examples of the separation compensation circuit 13. In the circuit shown in Figure 3,
A resistor 31 is connected between the output and the inverting input of the operational amplifier 14. Further, a series circuit of a variable resistor 32 and a capacitor 33 is connected between the inverting input of the operational amplifier 14 and the ground. Furthermore, in the circuit shown in FIG. 4, a variable resistor 3 is connected between the output of the operational amplifier 14 and the ground.
4 and a capacitor 35 are connected, and the movable terminal of the variable resistor 34 is connected to the inverting input of the operational amplifier 14.

As mentioned above, in the FM stereo receiver of the present invention,
Since the output signal of the FM detection means is directly supplied to the pulse noise detection system without passing through a high-frequency compensation HPF or the like, it is possible to maintain good pulse noise detection sensitivity.

Furthermore, if the output signal of the FM detection means is amplified in the separation compensation means and then subjected to separation compensation before being supplied to the stereo demodulation means, no insertion loss will occur.
Moreover, good separation can be obtained in the stereo demodulation means. Furthermore, since there is no need to use external components such as a variable resistor in the signal line from the FM detection means to the stereo demodulation means, there is an advantage that it is suitable for IC implementation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram specifically showing the separation compensation circuit in the receiver of FIG. 1, and FIGS. 3 and 4 are diagrams of the separation compensation circuit. A circuit diagram showing another circuit example, FIG. 5 is a block diagram showing a conventional example of an FM stereo receiver equipped with a pulse noise canceling device, and FIG. 6 is a concrete example of the separation compensation circuit in the receiver of FIG. FIG. 7 is a circuit diagram showing a delay circuit equipped with a separation compensation function. Explanation of symbols of main parts 1...FM detection circuit 2.13...Separation compensation circuit 3...
... Delay circuit 4 ... Gate circuit 6 ... Stereo demodulation circuit 8 ... Noise amplifier 9 ... Noise detection circuit 12 ... LPF Applicant Pioneer Corporation

Claims (2)

[Claims] (1) FM detection means for FM detecting a received signal;
noise detection means for detecting pulsed noise contained in the output signal of the M detection means and generating a cutoff signal; separation compensation means for compensating for separation of the output signal of the FM detection means; The present invention is characterized by comprising a suppression means for performing pulse noise suppression processing on the output signal of the separation compensation means and outputting the processed signal, and a stereo demodulation means for stereo demodulating the output signal of the suppression means. FM stereo receiver. (2) The FM stereo receiver according to claim 1, wherein the separation compensation means comprises amplification means having high-frequency boost characteristics.