JPH01256829A - Fm stereo receiver - Google Patents

Abstract

PURPOSE:To prevent deterioration in sound quality due to multi-path distortion by providing a suppression means suppressing a 2nd DC voltage to a 1st DC voltage or below to a difference voltage generating means generating a difference voltage between the 1st DC voltage and the 2nd DC voltage so as to allow the circuit to respond quickly to the occurrence of multi-path distortion. CONSTITUTION:When the output of an AM detection circuit 9 is smoothed by an LPF 10, the 1st DC voltage e1 changing in response to the IF signal level is generated. The output signal of a rectifier circuit 17 is smoothed by an LPF 18 and the output voltage of the LPF 18 is the 2nd DC voltage e2 in response to the amplitude of the multi-path distortion. A subtractor 24 subtracts the 2nd DC voltage e2 from the 1st DC voltage e1 and outputs a difference voltage e1-e2 as a control voltage. When a very large multi-path distortion takes place and the 2nd DC voltage e2 is going to exceed the 1st DC voltage e1, a limiter circuit is activated to discharge the electric charge in a capacitor 23 of the LPF 28 to ground. Thus, the difference voltage e1-e2 outputted from the subtractor 24 is kept always to zero V or over.

Description

[Detailed description of the invention] Technical field The present invention relates only to FM stereo receivers. A conventional example of an FM stereo receiver is shown in FIG.

In this receiver, FM broadcast waves arriving at an antenna 1 are amplified in a front end section 2 and converted into an intermediate frequency signal. After being amplified by an IF (intermediate frequency) amplifier 3 having a limiter function, the signal is applied to an FM detection circuit 4. The signal converted into a composite signal, which is an FM detection signal, in the detection circuit 4 is supplied to a pulse noise removing device 5. This pulse noise removing device 5 includes, for example, a gate circuit that allows the composite signal to pass through, a pulse detection circuit that detects a pulse component from the composite signal using a bypass filter and outputs the control signal, and a gate circuit that is cut off. and a hold circuit that outputs the level of the composite signal immediately before the cutoff when in the state. The output of the pulse noise remover 5 is supplied to a multiplex demodulation circuit 6 for obtaining left and right channel signals. The left and right channel signals are supplied to a separation control circuit 7 that controls separation (degree of separation), and further supplied to L and R output terminals via a frequency characteristic control circuit 8 that attenuates high frequency levels.

On the other hand, in order to detect a level proportional to the received electric field strength,
The IF signal level of the amplifier 3 is supplied to the AM detection circuit 9. The output signal of the AM detection circuit 9 is smoothed through an LPF (low pass filter) 10 consisting of a resistor 11 and a capacitor 12, and is applied as a control voltage to the separation control circuit 7 and frequency characteristic control circuit 8. In addition, A
The output signal of the M detection circuit 9 is used as a level signal to an S (signal) meter.

In such an FM stereo receiver, the output of the AM detection circuit 9 that detects the IF multiplied signal in the IF amplifier 3 is the LPFI signal.
When smoothed by O, a control voltage is generated that changes depending on the magnitude of the IF signal level. In accordance with this control voltage level, the separation control circuit 7 controls the degree of separation of the left and right channel signals, and the frequency characteristic control circuit 8
, the high frequency level of each channel signal is controlled.

That is, as the received signal level decreases, the degree of separation between left and right channel signals decreases, and the high frequency level of each channel signal is attenuated. This prevents deterioration of sound quality due to gradual changes in the electric field, that is, noise caused by weak electric fields or weak electric fields.

However, in such conventional FM stereo receivers, even if multipath interference occurs, the electric field variation due to the interference is attenuated by the LPFIO, so the degree of separation and high frequency level cannot be sufficiently controlled, and the multipath It has been difficult to effectively prevent sound quality deterioration due to distortion.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an FM stereo receiver that can quickly respond to the occurrence of multipath distortion and effectively prevent deterioration of sound quality due to multipath distortion.

In the FM stereo receiver of the present invention, an AM
a detection means; a first DC voltage generation means for generating a first DC voltage according to the output signal level of the AM detection means;
TS2 according to the AC component level in the output signal of the detection means
a second DC voltage generation means for generating a DC voltage; a difference voltage generation means for generating a difference voltage between the first DC voltage and the second DC voltage; an FM detection means for FM detection of an intermediate frequency signal; and stereo demodulation means for stereo demodulating the output signal of the means with demodulation characteristics according to the differential voltage level.
The stereo receiver is characterized in that the differential voltage generating means includes suppressing means for suppressing the second DC voltage to be lower than the first DC voltage.

EXAMPLE Hereinafter, an example of the present invention will be described in detail with reference to FIG.

In the FM stereo receiver shown in FIG. 1, which is an embodiment of the present invention, the same parts as those in the receiver shown in FIG.
It is connected to the IO and also to the capacitor 15. Capacitor 15 extracts the AC component in the output signal of AM detection circuit 9. On the other hand, an HPF (bypass filter) 20 is provided to extract high frequency components from the output signal of the FM detection circuit 4. The output signal of the HP F 20 is added to the output signal of the capacitor 15 by an adder 21 and then supplied to the amplifier 16. A rectifier circuit 17 is connected to the output of the amplifier 16, and an LPF 18 is further connected to the output of the rectifier circuit 17. The LPF 18 includes a resistor 22 and a capacitor 23. The output of this LPF 18 and the output of LPFIO are connected to a subtracter 24. The subtracter 24 outputs a voltage obtained by subtracting the output voltage of the LPF 18 from the output voltage of the LPFIO. This subtractor 24
The voltage output from the control circuit 7 is supplied to the separation control circuit 7 and the frequency characteristic control circuit 8 as a control voltage.

Furthermore, in the FM stereo receiver according to the present invention, L
A limiter circuit consisting of an operational amplifier 25 and a PNP transistor 26 is connected as a suppressing means between the output of the PF 18 and the output of the LPFIO. That is, the inverting input terminal of the operational amplifier 25 is connected to the output of the LPF 18 together with the emitter of the transistor 26, and the non-inverting input terminal is connected to the output of the LPFIO. The output terminal of the operational amplifier 25 is connected to the base of a transistor 26, and the collector of the transistor 26 is connected to ground. The rest of the configuration is the same as the receiver shown in FIG. In addition,
The multiplex demodulation circuit 6, the separation control circuit 7 and the frequency characteristic control circuit 8 form stereo demodulation means.

In the FM stereo receiver according to the present invention having such a configuration, when the output of the AM detection circuit 9 that detects the IF multiplied signal in the IF amplifier 3 is smoothed by the LPFIO, the first DC signal changes depending on the magnitude of the IF signal level. A voltage e1 is generated. On the other hand, if multipath exists, the IF multiplied signal amplitude within the IF amplifier 3 changes and an envelope component is generated. The signal level of this envelope component corresponds to the magnitude of multipath distortion. Therefore, AM detection circuit 9
The output signal is supplied to the capacitor 15, whereby the AC component of the output signal from the AM detection circuit 9, that is, the envelope component in the IF signal due to multipath distortion is extracted. Furthermore, a high frequency component, that is, a component including multipath distortion, is extracted from the output signal of the FM detection circuit 4 by the HPF 20 . Output voltage of capacitor 15 and HPF
The output voltages of 20 are added by an adder 21 and supplied to an amplifier 16, and the amplified output from the amplifier 16 is rectified in a rectifier circuit 17. The output signal of the rectifier circuit 17 is smoothed by the LPF 18, and the output voltage of the LPF 18 becomes a second DC voltage e2 depending on the magnitude of multipath distortion. The subtracter 24 subtracts the second DC voltage e2 from the first DC voltage e1 and outputs a differential voltage el-e2 as a control voltage.

The control voltage changes depending on the received signal level, but when multipath occurs, it decreases depending on the magnitude of multipath distortion. In accordance with this control voltage level, the separation control circuit 7 controls the degree of separation of the left and right channel signals, and the frequency characteristic control circuit 8 controls the high frequency level of each channel signal. Therefore, as the received signal level decreases and as the magnitude of multipath distortion increases, the degree of separation between left and right channel signals decreases, and the high frequency level of each channel signal is attenuated.

In such an operation, if very large multipath distortion occurs, there is a possibility that the second DC voltage e2 exceeds the first DC voltage e1. However, the second DC voltage e2
When the voltage exceeds the first DC voltage e1, the limiter circuit described above operates to discharge the charge in the capacitor 23 of the LPF 18 to the ground via the emitter-collector of the transistor 26, thereby increasing the second DC voltage e2. The voltage is approximately equal to the first DC voltage e1. Therefore, the differential voltage el-el output from the subtracter 24 is always maintained at 07 or higher.

FIG. 2 shows another embodiment of the invention. In this FM stereo receiver, the differential voltage generating means is the current source 27.
, a buffer amplifier 28 and a resistor 29. The output voltage of LPFlo, that is, the first DC voltage e1 is passed through the buffer 7 amplifier 28 and the resistor 29 to a current 1iX2.
7 and the magnitude of the current flowing through the current source 27 is LP
It is controlled by the second DC voltage e2 output from F18.

As a result, as the second DC voltage e2 increases, the current flowing through the current source 27 increases, and the control voltage supplied to the separation control circuit 7 and the frequency characteristic control circuit 8 decreases. The rest of the configuration is the same as that of the receiver shown in FIG.
It may also be installed inside.

In each of the embodiments of the present invention described above, the AC component of the output signal of the AM detection circuit 9 and the high frequency component of the output signal of the FM detection circuit 4 are added by the adder 21 and the amplifier 1
However, only the AC component of the output signal of the AM detection circuit 9 may be supplied to the amplifier 16.

As described above, the FM stereo receiver of the present invention has the following effects:
By generating a first DC voltage according to the signal level of the IF multiplied signal and AM detection, and extracting the AC component level from the AM detected signal, an IF multipath signal envelope component due to multipath is obtained, and the AC component level is Second according to
It is possible to generate a DC voltage and perform stereo demodulation of the output signal of the FM detection circuit with demodulation characteristics such as the amount of muting, the degree of separation, and the amount of high-frequency attenuation according to the voltage difference between the first DC voltage and the second DC voltage. It is done. In other words, since the degree of separation and high-frequency attenuation during stereo demodulation can be controlled according to the magnitude of multipath distortion, it is possible to quickly respond to the occurrence of multipath and reduce auditory distortion. . Further, since a suppressing means is provided for suppressing the second DC voltage below the first DC voltage, when a large multipath disturbance occurs, the first DC voltage '! This prevents the voltage difference from the .82 DC voltage from decreasing too much, and it is possible to quickly return to a good stereo condition after the multipath interference disappears.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing another embodiment of the invention, and FIG. 3 is a block diagram showing a conventional example of an FM stereo receiver. Explanation of symbols of main parts 3... IF amplifier circuit 4... FM detection circuit 5... Pulse noise removal device 6... Multiplex demodulation circuit 7・・・・・・
・Separation control circuit 8...Frequency characteristic control circuit 10.18...LPF 21...Adder 24...Subtractor 27... Current source applicant Pioneer Corporation

Claims (3)

[Claims] (1) AM detection means for performing AM detection on an intermediate frequency signal obtained by frequency converting a received signal; and first DC voltage generation means for generating a first DC voltage according to the output signal level of the AM detection means. , second DC voltage generation means for generating a second DC voltage according to the AC component level in the output signal of the AM detection means; and a differential voltage for generating a difference voltage between the first DC voltage and the second DC voltage. An FM stereo receiver comprising a generating means, an FM detecting means for FM detecting the intermediate frequency signal, and a stereo demodulating means for stereo demodulating the output signal of the FM detecting means with demodulation characteristics according to the differential voltage level. The FM stereo receiver is characterized in that the differential voltage generating means includes suppressing means for suppressing the second DC voltage to be lower than the first DC voltage. (2) The second DC voltage generation means includes an extraction means for extracting a high frequency component of the output signal of the FM detection means, and the second DC voltage generation means
2. The FM stereo receiver according to claim 1, wherein the AC component level is extracted from a signal obtained by adding the output signal of the M detection means and the high frequency component of the output signal of the FM detection means. (3) The FM stereo receiver according to claim 1, wherein the suppressing means comprises a limit circuit.