JPS6046132A - Radio receiver - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to AM or FM radio receivers.

1. Configuration of conventional example and its problems FIG. 1 shows an outline of a conventional F'M radio receiver. In FIG. 1, 1 is an antenna, 2 is an antenna tuning circuit, 3 is a high frequency amplifier, and 4 is a T'%, F, tuning circuit. 5 is a local oscillator, 6 is a mixer, 72 is an intermediate frequency transformer, 8 is an intermediate frequency amplifier, 9 is an FM detector, 10 is a stereo demodulator, 11 is a low frequency power amplifier, 12-L, 1. 2-R are right and left speakers, respectively. 13 is an AGC circuit. Furthermore, the component surrounded by a dotted line is a front end section which is an integrated circuit.

Next, the operation of the conventional example will be explained. In FIG. 1, an antenna 1 receives a radio wave, an antenna tuning circuit 2 selects a desired radio wave, a high frequency amplifier 3 amplifies it,
Furthermore, the desired wave is selected by the R1E tuning circuit 4, and the mixer 6
Here, a signal of the difference in frequency between the output oscillated by the local oscillator 5 and the desired wave, that is, a signal component of an intermediate frequency, is created.The intermediate frequency transformer 7 extracts only the intermediate frequency signal and converts this into an intermediate frequency signal. Amplify with frequency amplifier 8,
An FM detector 9 converts the intermediate frequency F'M signal into an audio signal. In the case of stereo broadcasting, the stereo demodulator 10 separates this audio signal into a right channel and a left channel, each of which is amplified by a low frequency power amplifier ]1, and then sent to a speaker 12-3 page γ R,, 1, 2-L. is driven and played as sound. AG
The C circuit 13 detects the intermediate frequency output of the mixer 6 and outputs a DC voltage to control the gain of the high frequency amplifier 3 so that the intermediate frequency output is equal to or less than a set value.

FIG. 2 shows the relationship between the signal input level of the conventional mixer 6 and the antenna signal input level.

The antenna signal input level (hereinafter referred to as antenna input) is 1. Until then, the input level of the mixer 6 (hereinafter referred to as MIX input) increases according to the antenna input.

Antenna input is 1. When it becomes larger, the AGC circuit 13 works, and as a result, the MIX input becomes constant. However, if the antenna input becomes larger than 12, it will exceed the control range of the AGC circuit 13, and the A, GC circuit 13 will no longer be able to control the M1'X human power, and as the antenna input increases, the MIX input will increase again. . 0. indicates that distortion occurs in the signal due to a large amount of MIX input, and the distortion reaches a limit level that can be confirmed by sound as a low frequency signal after Ii"M detection. In other words, MIX input of 01 or higher is unique as an interfering signal. Kaisho GO-46132 (2) If present, distortion such as intermodulation interference occurs and is confirmed as sound.

As described above, the conventional circuit has the disadvantage that when there is an antenna input that exceeds the control range of the AGC circuit 13, distortion due to interference waves becomes noticeable.

OBJECTS OF THE INVENTION The present invention eliminates the drawbacks of the conventional example described above, and provides a radio receiver in which distortion due to interference waves is less likely to occur even with a large antenna input.

Structure of the Invention In order to achieve the above object, the present invention detects the antenna signal input level and automatically activates an attenuator when the antenna signal input level reaches a predetermined level, thereby eliminating distortion caused by large input interference waves. This is something that can be reduced.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below. In addition, the third
In the figure, the same parts as in FIG. 1 are given the same numbers. In FIG. 3, reference numerals 14 denote R, F, and a control circuit that detects the high frequency signal output level of the tuning circuit 4, compares it with a predetermined 5 page value, and generates a corresponding control signal;
5 is an automatic attenuation circuit controlled by a control signal output from the control circuit 14.

FIG. 4 shows the control circuit 14 and automatic attenuation circuit 1 of the above embodiment.
5 is shown. In FIG. 4, 16 is a buffer amplifier, 17 is an amplifier, 18 is a detector, 19 is a voltage comparator,
20 indicates a driver, and 21 indicates an automatic attenuator.

Next, the operation of the second embodiment will be explained. In FIG. 4, RoF and the output of the tuning circuit 4 are added to the input terminal of the buffer amplifier 16, but the influence on l"t, F, the tuning circuit 4, and the mixer 6 is reduced.

The high frequency signal taken out by the buffer amplifier 16 is amplified by the amplifier 17, and the detector 18 outputs a DC voltage according to the input high frequency signal level. Voltage comparator 19
, compare the DC voltage output from the detector 18 with the set value, and if the output level is lower than the set value, for example, 8V.
If the value is equal to or greater than 1 set value, a direct current voltage of QV is generated. The output voltage of the voltage comparator 19 is input, and the driver 20 operates the automatic six-vane attenuator 21. The setting value of the voltage comparator 19 is
By setting R, , F in correspondence with the high frequency output level of the tuning circuit 4, the on/off level of the automatic attenuator 21 can be set.

In this embodiment, when the antenna input level becomes too high, the attenuator is automatically activated to attenuate the input signal level by a predetermined amount, which has the advantage of reducing distortion from interfering silver at the time of large input.

Although the above embodiment is an example of an FPyI receiver, the present invention can also be applied to an AM receiver or the like.

Effects of the Invention The present invention has the above configuration, and since the attenuator is operated at the antenna input terminal when the antenna input level is above a predetermined value, distortion can be reduced when the antenna input is large.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional FM radio receiver, Fig. 2 is a diagram showing the relationship between the antenna input level of the FM radio receiver and the mixer input level, and Fig. 3 is an embodiment of the present invention. Figure 4 is a block diagram of the automatic attenuator and control circuit of the FM radio receiver. 1. Antenna, 2... Antenna tuning circuit, 3...
High frequency amplifier, 4...LP, tuning circuit, 5...local oscillator, 6...mixer, 7. intermediate frequency transformer, 8.
...Intermediate frequency amplifier, 9...FM detector, 10...Stereo demodulator, 1]...Low frequency power amplifier, 12-L,
12-R. ... Speaker, 13 ... AGC circuit, 14 ... Control circuit, 15 ... Automatic attenuation circuit, 16 ... Buffer amplifier, 17 ... Amplifier, ]8 ... Detector, 19.
...Voltage comparator, 20...Driver, 21...Automatic attenuator.

Claims (1)

[Claims] A high frequency amplification circuit, a mixer to which the output of the high frequency amplification circuit is applied, a control circuit that detects the signal input level of this mixer and outputs a control signal, and an automatic What is claimed is: 1. A radio receiver comprising: an attenuation circuit; the automatic attenuation circuit is controlled by a control signal output from the control circuit.