JPH01232845A - Fm stereo receiver - Google Patents

Abstract

PURPOSE:To quickly reduce multi-path distortion by using a charging means so as to smooth an AM detection signal in an IF signal, discharging the charging means in response to the decreasing change of the level of the AM detection signal and demodulating the output signal of the FM detection means in response to the output voltage of the charging means. CONSTITUTION:When an output of an AM detection circuit 9 being the result of detecting an IF signal in an IF amplifier 3 is smoothed by an LPF 10, a control voltage is generated, whose level varies with the quantity of the IF signal level. On the other hand, if any multi-path exists, since the amplitude of the IF signal in the IF amplifier drops rapidly, a transistor(TR) 13 is turned on and the charge stored in a capacitor 12 flows to ground. Then the control voltage outputted from the LPF 10 is lowered, then the degree of separation of left/right channel signals of a separation control circuit 7 is decreased in response to the control voltage level. Thus, as soon as the multi-path is generated, the multi-path distortion is reduced.

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 high-pass 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 by 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 fluctuation due to the interference is attenuated by the LPFIO, so the degree of separation and high frequency level cannot be controlled sufficiently, and the It has been difficult to effectively prevent sound quality deterioration due to path 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 FM
FM stereo reception comprising a detection means, an intensity signal generation means for generating an intensity signal indicating the intensity of an intermediate frequency signal, and a stereo demodulation means for stereo demodulating the output signal of the FM detection means with demodulation characteristics according to the intensity signal. The intensity signal generation means includes an AM detection means for performing AM detection on the intermediate frequency signal, a charging means for generating an intensity signal by being charged by the output voltage of the AM detection means, and a decreasing change in the output voltage of the AM detection means. The battery is characterized by having a discharging means for discharging the charging means accordingly.

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. There is.

That is, the base of the transistor 13 is connected to the AM of the resistor 11.
It is connected to one end on the detection circuit 9 side, its emitter is connected to a connection line between a resistor 11 and a capacitor 12, and its collector is connected to ground. The rest of the configuration is the same as the receiver shown in FIG.

Note that 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, a control voltage ( intensity signal) is generated. On the other hand, if a multipath exists, as shown in FIG. 2, the amplitude of the IF multiplied signal in the IF amplifier 3 decreases rapidly, so that the base voltage of the transistor 13 is lower than the voltage across the capacitor 12, that is, the emitter voltage of the transistor 13. Become. This turns on the transistor 13, and the charge stored in the capacitor 12 flows as a current to the ground via the emitter and collector of the transistor 13. Therefore, since the control voltage output from the LPFIO, that is, the voltage across the capacitor 12, decreases, the degree of separation between the left and right channel signals is reduced by the separation control circuit 7 in accordance with this control IM pressure level.
Further, the frequency characteristic control circuit 8 attenuates the high frequency level of each channel signal. In this way, transistor 1
3 is turned on at the same time as multipath occurs, and the capacitor 12 is immediately discharged, so that the degree of separation and the amount of high-frequency attenuation are controlled as described above, and multipath distortion can be reliably reduced.

3 through 5 each show a portion of another embodiment of the invention. In the receiver shown in FIG. 3, the base of transistor 3 is connected to resistor 1 through capacitor
1 on the AM detection circuit 9 side, and a resistor 15 is connected in parallel between the base and emitter of the transistor 13.

This capacitor 14 and resistor 15 constitute an HPF (/1 pass filter). The rest of the configuration is the same as that of the receiver shown in FIG. In this configuration, only the high-frequency component in the output signal of the AM detection circuit 9 is transmitted to the transistor 1.
Supplied on the base of 3.

Therefore, only the signal when the multipath occurs and the signal amplitude rapidly decreases by IF is extracted by the capacitor 14 and the resistor 15. Therefore, the transistor 13 is turned on only for multipath, and the capacitor 12 is discharged.

In the receiver shown in FIG. 4, the LPFIO consists of a resistor 11, 16 and a capacitor 12 connected in series,
The emitter of transistor 13 is connected to the connection point of resistor 11.16. In the receiver shown in FIG. 5, the emitter of the transistor 13 is connected via a resistor 17 to a connection line between the resistor 11 and the capacitor 12. The other configurations of the receiver shown in FIGS. 4 and 5 are similar to the receiver shown in FIG. 3. In the receiver shown in FIGS. 4 and 5, when transistor 13 is turned on, current from capacitor 12 flows through resistor 16 or 17 and transistor 13 to ground. Therefore, the discharge rate, that is, the rate of decrease in the voltage across the capacitor 12, is slower than in the receivers shown in FIGS. 1 and 3, and separation control and high-frequency attenuation control can be performed without causing discomfort when multipath occurs. can be done.

Note that in each of the embodiments of the present invention described above, the transistor 13 is turned on due to the occurrence of multipath;
The capacitor 12 may be discharged with an amount of current depending on the magnitude of multipath distortion by the transistor 13 becoming active in accordance with the output signal level of the AM detection circuit 9.

As described above, the FM stereo receiver of the present invention has the following effects:
The IF multiplied signal AM detection signal is smoothed by a charging means, and A
The charging means is discharged in response to a decreasing change in the M detection signal level, and the output signal of the FM detection means is stereo demodulated with demodulation characteristics such as miniaturization amount, separation degree, and high frequency attenuation amount according to the output voltage of the charging means. will be carried out. Therefore, since the output voltage of the charging means decreases when multipath occurs, it is possible to quickly respond to the occurrence of multipath and reduce multipath distortion regardless of the relatively simple circuit configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram showing changes in the AM detection signal due to multipath, and FIG.
5 through 5 are circuit diagrams showing a part of another embodiment of the present invention, and 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...LPF Applicant: Pioneer Corporation

Claims (3)

[Claims] (1) FM detection means for performing FM detection on an intermediate frequency signal obtained by frequency converting a received signal; an intensity signal generation means for generating an intensity signal indicating the strength of the intermediate frequency signal; and an output of the FM detection means. FM stereo demodulation means for stereo demodulating a signal with demodulation characteristics according to the intensity signal.
In the stereo receiver, the intensity signal generating means includes an AM detection means for performing AM detection on the intermediate frequency signal;
An FM stereo characterized by having a charging means that is charged by the output voltage of the detection means to generate the intensity signal, and a discharging means that discharges the charging means in response to a decreasing change in the output voltage of the AM detection means. Receiving machine. (2) The charging means comprises a low-pass filter equipped with a resistor and a capacitor, and the discharging means comprises a switching element connected in parallel to the capacitor and turned on in response to a decrease in the output voltage of the AM detection means. FM stereo receiver according to claim 1. (3) The charging means includes a low-pass filter including a resistor and a capacitor, and the discharging means includes a high-pass filter connected in parallel to the capacitor and supplied with the output voltage of the AM detection means, and the output voltage of the high-pass filter. 2. The FM stereo receiver according to claim 1, further comprising a switching element that becomes conductive in response to a decreasing change in .