JPS5991751A - Radio receiver - Google Patents

Abstract

PURPOSE:To reduce surely multi-path disturbing noise by rectifying an output of a detecting circuit which detects an intermediate frequency signal, and controlling the separation degree of a stereo demodulating circuit by a synthesized signal of the detected output and the rectified output. CONSTITUTION:A voltage in response to an electric field strength is outputted to a terminal (a) of an intermediate frequency amplifier circuit 5, detected at a diode 9 and outputted to a terminal (b). When multi-path disturbance is received, a DC voltage VD and an AC voltage va are applied to the terminal (b), the voltage va is extracted by a capacitor C12, rectified at diodes 13, 14, C15 and a resistor 16 and converted into a DC voltage. If the multi-path disturbance is large and the voltage va is large, the potential at a point (c) is increased, the output impedance of transistors 17, 18 is decreased, and the potential at the terminal (b) is reduced. Then, the separation of the stereo demodulating circuit 6 is decreased and the multi-path disturbing noise is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates in particular to an FM stereo type radio receiver for use in a vehicle.

Conventional configurations and their problems In recent years, FM broadcasting has entered the era of multiple stations, and FM stereo radio receivers have been increasingly used as sources of highly musical quality in car radio receivers. FM radio waves have shorter wavelengths than medium waves, and it is said to be difficult to receive them in good radio conditions when cars are constantly moving. -For example, noise and distortion caused by multipath interference are major factors that impair sound quality. Many attempts have been made to eliminate and reduce this multi-noise interference, some of which are listed below.

■ A method to control the degree of separation of a stereo demodulation circuit according to electric field fluctuations.

■ A method of controlling the high frequency band of the stereo demodulation output according to electric field fluctuations.

■ A method that uses multiple receiving antennas and selects them according to the radio wave conditions.

There are many other measures that can be considered, but to briefly explain the features of items 1 to 2 above, 2 and 2 cannot be expected to provide sufficient improvement due to electric field fluctuations, and method 2 also has multi-nox interference on multiple antennas at the same time. If this happens, it cannot be removed, and the cost of the device itself increases.

Conventionally, this type of multipath interference has been reduced in most cases by the methods (1) and (3) mentioned above, and the conventional examples thereof will be explained below with reference to FIG.

1 is a receiving antenna, 2 is a high frequency amplification circuit, 3 is a mixing circuit, 4 is a local oscillation circuit, 5 is an intermediate frequency amplification circuit, 6 is a stereo demodulation circuit, 7 is a low frequency amplification circuit, and 8 is a speaker. A terminal a is output from the intermediate frequency amplification circuit 5 and is connected to the stereo demodulation circuit 6 via a diode 9 and a terminal A.

Further, the terminal is grounded via a resistor 10 and a capacitor 11.

Based on the above configuration, an intermediate frequency signal corresponding to the electric field strength is normally output to terminal a according to the characteristics shown in FIG. is applied to the terminal. The terminal S is a terminal for controlling the degree of separation of the stereo demodulation circuit 6 using a DC voltage, and its characteristics are as shown in FIG.

When multipath interference occurs, it is equivalent to when the electric field strength decreases, so the potential at terminal a decreases according to the characteristics shown in FIG. 2. This drop variation is made up of diode 9 and resistor 1.
0, the signal is detected by the capacitor 11, and the potential of the terminal is lowered, the degree of separation of the stereo demodulation circuit 6 is destroyed, and noise due to multipath interference is reduced. The problem here is that when multipath interference occurs, the potential at terminal a fluctuates with a waveform as shown in FIG. 4 depending on the radio wave condition.

At this time, although the detection output is subject to multipath interference, the DC voltage VD and AC voltage va shown in Fig. 5 are applied to the terminals, so the degree of separation of the stereo demodulation circuit 6 cannot be controlled and the noise is reduced. It is something that cannot be done.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and provides a radio receiver that has a simple configuration and is capable of reliably eliminating the interference noise.

Structure of the Invention The present invention includes a detection circuit for detecting an intermediate frequency signal and a rectification circuit for rectifying the output of the detection circuit, and a signal obtained by combining the detection output of the detection circuit and the rectification output of the rectification circuit is used to generate a stereo demodulation circuit. By controlling the degree of separation, multi-noise interference noise can be significantly reduced.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. In FIG. 6, parts that are the same as those in the conventional example shown in FIG. 1 are given the same numbers and their explanations will be omitted.

Connect the terminal to the anode via capacitor 12 (fil
l iK is connected to the cathode side of the diode 13 which is grounded, and its connection point is connected via the diode 14 to the base of the transistor 17.18. 15 is a resistor, 16 is a capacitor, and these are transistors 17
．． 18 base and ground. The emitter of the transistor 17 is connected to the collector of the transistor 18, and the collector of the transistor 17 is connected to the emitter of the transistor 18. The emitter side of the transistor 17 is grounded, and the collector side is connected to a terminal.

The operation based on the above configuration will be explained.

As in the conventional flJ, a voltage according to the electric field strength is outputted to the terminal a, and the wave is detected and applied to the terminal A. Next, a case will be explained in which a waveform as shown in FIG. 4 is output from terminal output 1 when multi-signal interference is received. At this time, a direct current voltage (2) detected by a diode 9 and an alternating current voltage (va) as shown in FIG. 5 are applied to the terminals. This AC voltage va is taken out with capacitor 2.
6 to rectify and convert to DC voltage. The Martinos interference force received here; if the AC voltage va becomes large, C5
The potential of the tunnel rises according to the characteristics shown in Figure 7, and the potential of the tunnel increases.
The output impedance of register 17.18 is lowered by i1,
The potential of the standing high riser drops as shown in FIG. Therefore, the separation degree of the stereo demodulation circuit 6 is 75, and the multi-noise interference noise is reduced.

On the other hand, when there is no multi-nox interference, the AC voltage va
is small, therefore the output impedance of the transistor 18 is also large, and the potential at the terminal does not drop, so the degree of isolation of the stereo demodulation circuit 6 is maintained at a high level. That is, in the present invention, when multipath interference occurs and the AC component V is large, the degree of separation of the stereo demodulation circuit 6 is controlled by the rectified output of the transistors 17 and 18, whereas when the electric field strength simply decreases, the degree of separation of the stereo demodulation circuit 6 is controlled by the conventional example. Similarly, the degree of separation is controlled by the detection output.

Here, the voltage applied to the terminal (control voltage)
The relationship between V and AC voltage V will be explained with reference to FIG. A shows the characteristic when AC voltage va is most likely to be generated due to multipath interference, and in this case, the control voltage to the stereo demodulation circuit 6 changes depending on the electric field strength. - An auspicious day is a characteristic when a large AC voltage va occurs due to multipath interference. In this case, even if the electric field strength is large, the control voltage is kept low and no longer depends on the electric field strength, and changes according to the AC voltage va. . Ha, 2 is the middle value between A and Mou.

Effects of the Invention As is clear from the embodiments described above, the present invention provides a detection circuit for detecting an interlayer wave signal in Fig. 1 and a rectification circuit for rectifying the detection output, and synthesizes the rectified output and the detection output. This system controls the degree of separation of the stereo demodulation circuit by using the following methods.This method can significantly reduce multipath interference noise, and can be realized at low cost with a simple configuration, making it highly practical. is a dog.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional example, Figs. 2 to 5 are characteristic diagrams for explaining the same operation, Fig. 6 is a circuit diagram showing an embodiment of the present invention, and Figs. 7 to 9 are the same. It is a characteristic diagram for explaining operation. 1...--Receiving antenna, 5...Intermediate frequency amplification circuit, 6... -Stereo demodulation circuit, 9...
・Diode, 13゜14・・・Diode, 1
7.18...transistor. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 6
Figure 3 Figure 4 Figure 5 Figure 7 Figure 8

Claims (1)

[Claims] It has an intermediate frequency amplification circuit that is equipped with a first terminal that outputs an intermediate frequency signal according to the electric field strength, and a stereo demodulation circuit that is equipped with a second terminal that can control the degree of separation with a DC voltage, A detection circuit that detects an intermediate frequency signal is connected to the terminal, a rectifier circuit that rectifies the detection output is connected to the detection circuit, and the detection output of the detection circuit and the rectified output of the rectification circuit are combined and sent to the second terminal. A radio receiver configured to supply