JPH01231440A - Fm stereo receiver - Google Patents

Abstract

PURPOSE:To prevent deterioration in sound quality due to multi-path distortion caused in response to multi-path distortion by applying stereo demodulation to an output signal of an FM detection means according to the demodulation characteristic in response to a differential voltage level. CONSTITUTION:An output signal from an AM detecting circuit 9 is fed to a capacitor 15 via a clip circuit 14, and an AC component in the output signal from the AM detecting circuit 9, that is, the envelope component in an IF signal caused by multi-path distortion is extracted. The AC component is amplified by an amplifier 16, fed to a rectifying circuit 17, where the component is rectified, and its output signal is smoothed by an LPF(low pass filter) 18 into a 2nd DC voltage. As the DC voltage is increased, the electric charge stored in a capacitor 12 of the LPF 10 is discharged and a control voltage is decreased in response to the magnitude of multi-path distortion. The separation of left/ right control channel signals is controlled by a separation control circuit 7 in response to the control voltage level and a frequency characteristic control circuit 8 controls a high frequency level of each channel signal. Thus, the deterioration in sound quality is prevented.

Description

[Detailed description of the invention] Technical field The present invention relates to an FM stereo receiver.

Background technology 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. These 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 LPFI.
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 fluctuation due to the interference is attenuated by the LPFIO, so the degree of separation and high frequency level cannot be sufficiently controlled, resulting in multipath distortion. It has been difficult to effectively prevent sound quality deterioration due to

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 clipping means for fixing a signal below a predetermined level of the output signal of the AM detection means to a predetermined level;
means for generating a first DC voltage according to the output signal level of the detection means; means for generating a second DC voltage according to the AC component level in the output signal of the clipping means; the first DC voltage and the second DC voltage; voltage difference generation means for generating a difference voltage between the FM signal and the FM detection means for FM detecting the intermediate frequency signal;
The present invention is characterized by comprising stereo demodulation means for stereo demodulating the output signal of the M detection means with demodulation characteristics according to the differential voltage level.

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 clip circuit 14.

As shown in FIG. 2, the clip circuit 14 includes differentially connected NPN transistors 21 and 22, and transistors 21.
22, and a current source 23 connected to the emitter of 22. The base of the transistor 21 serves as an input, an AM detection signal is supplied from the AM detection circuit 9 to the base, and the emitters of the transistors 21 and 22 serve as outputs. A predetermined voltage V approximately equal to the clip level is applied from a voltage source 24 to the base of the transistor 22 . The clip level is the voltage V between the base and emitter of the transistor 22 from the predetermined voltage V.
9ε is subtracted from the voltage V−V9E.

A capacitor 15 is connected to the output of the clip circuit 14. Capacitor 15 extracts the AC component in the output signal of clip circuit 14. A rectifier circuit 17 is connected to the output of the capacitor 15 via an amplifier 16, and an LPF 18 is further connected to the output of the rectifier circuit 17.

On the other hand, a current source 19 is connected between the output line of the LPFIO, that is, the control voltage supply line to the separation control circuit 7 and frequency characteristic control circuit 8, and the ground. This current source 19 causes a current corresponding to the output voltage level of LPFlg to flow from the LPF 10 to the 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 has detected the IF multiplied signal in the F amplifier 3 is smoothed by the LPFIO, a control voltage (first DC voltage) that changes depending on the magnitude of the IF signal level 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, the output signal from the AM detection circuit 9 is passed through the clip circuit 14 to the capacitor 15.
The alternating current 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. This alternating current component is amplified by an amplifier 16, and then supplied to a rectifier circuit 17 where it is rectified. The output signal of the rectifier circuit 17 is smoothed by LPFlg to become a second DC voltage. This DC voltage becomes a voltage according to the magnitude of multipath distortion, and as this DC voltage increases, a current flows to the current source 19 and the LPFIO
The electric charge stored in the capacitor 12 is discharged. That is, the second DC voltage is subtracted from the first DC voltage. Therefore, depending on the magnitude of multipath distortion, capacitor 1
2, the control voltage decreases. 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.

The clip circuit 14 cuts the signal whose output voltage level of the AM detection circuit 9 is lower than the above voltage v-vBε, and outputs the signal to the voltage V-.
be equal to Veε. Among the output signals of the AM detection circuit 9, the level of the DC component due to the received radio wave signal increases as the electric field becomes stronger, as shown by the solid line in FIG. 3, and the level of AC components such as white noise is shown by the broken line in FIG. As shown above, it increases in weak electric fields. That is, in a weak electric field, the output signal of the AM detection circuit 9 contains many white noise components as shown in FIG. Almost all noise components are removed. In a weak electric field, the AM detection circuit 9
The output signal has less white noise components as shown in FIG. 4(b) and more received radio wave signals, so by passing through the clip circuit 14, the level is reduced as shown in FIG. 5(b). White noise components will be removed. In addition, in a medium-strong electric field, the output signal of the AM detection circuit 9 has a high DC component level due to the received radio wave signal as shown in FIG. 4(c), and almost no white noise component is present. Figure 5 (c)
The signal waveform does not change as shown in . Furthermore, in a weak electric field or weak electric field, even if multipath exists, it will be masked by the white noise component, making it impossible to detect envelope components due to multipath. Therefore, the clip circuit 14 can cause the capacitor 1 to
5, almost no AC signal is output, multipath detection is stopped, and the degree of separation of left and right channel signals and the high frequency level are controlled according to the output voltage of LPFlo.

In the above embodiment, the second DC voltage is subtracted from the first DC voltage by discharging the charge in the LPFlo capacitor 12 using the current source 19. It may be subtracted by a voltage subtractor.

As described above, the FM stereo receiver of the present invention has the following effects:
generating a first DC voltage according to the AM-detected signal level of the IF-multiplied signal, and extracting an AC component level from the AM-detected signal via a clip means to obtain an IF-multiplied signal envelope component by multipath; A second DC voltage is generated according to the AC component level, and the output signal of the FM detection means is detected with demodulation characteristics such as separation degree and high-frequency attenuation amount according to the voltage difference between the first DC voltage and the second DC voltage. Stereo demodulation is performed. Therefore, it is possible to control the degree of separation and the amount of high-frequency attenuation during stereo demodulation according to the magnitude of multipath distortion, so it is possible to quickly respond to the occurrence of multipath and reduce auditory distortion. . In addition, since the clipping means cuts the AM detection signal below a predetermined level and fixes it at a predetermined level, it is possible to avoid an increase in the second DC voltage level due to a weak electric field or white noise that often occurs in a weak electric field. This prevents the degree of separation from decreasing unnecessarily or increasing the amount of high-frequency attenuation when no path interference occurs.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a specific configuration of the clip circuit in the receiver shown in FIG. 1, and FIGS. FIG. 6 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 14...Clip circuit 19...Current source applicant Pioneer Corporation

Claims (1)

[Claims] The intermediate frequency signal obtained by frequency converting the received signal is
AM detection means for detecting a wave; clip means for fixing a signal below a predetermined level of the output signal of the AM detection means to the predetermined level; and means for generating a first DC voltage according to the output signal level of the AM detection means. and means for generating a second DC voltage according to the AC component level in the output signal of the clipping means; differential voltage generating means for generating a differential voltage between the first DC voltage and the second DC voltage; An FM stereo receiver comprising: FM detection means for FM detecting an intermediate frequency signal; and stereo demodulation means for stereo demodulating the output signal of the FM detection means with demodulation characteristics according to the differential voltage level.