JPS6091730A - Radio receiver - Google Patents

Abstract

PURPOSE:To reduce distortion by operating an attenuation circuit from an antenna input terminal when an antenna input level is a prescribed value or over. CONSTITUTION:A control voltage from an AGC circuit 13 is compared with a reference voltage fed to a terminal 42 by an operational amplifier 33 of a control circuit 14. When an output of the operational amplifier 33 is at a low level, a diode 23 is turned on, a diode 24 is turned off and a signal coming from an antenna terminal 20 is transmitted without being attenuated. When the control voltage is larger than the reference voltage, since an output of the operational amplifier 33 goes to a high level, the diode 23 is turned off and the diode 24 is turned on, and the signal coming from the antenna input terminal 20 receives the attenuation decided by resistors 22 and 25.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an AMt only PM radio receiver.

Conventional configuration and problems thereof FIG. 1 shows an outline of a conventional FM radio receiver. In Figure 1, 1 is an antenna, 2 is an antenna tuning circuit, 3 is a high frequency amplifier circuit, 4 is an R, F tuning circuit, 5 is a local oscillator, 6 is a mixer, 7 is an intermediate frequency lance, 8 is an intermediate 9 is an FM detector, 10 is a stereo demodulator, 11 is a low frequency power amplifier, and 12R and 12L are right and left circular speakers, respectively. 13 is an AGC circuit. Note that the component surrounded by the dotted line is the front end section.

Next, the operation of the conventional example will be explained. In Fig. 1, the antenna receives a radio wave, the antenna tuning circuit 2 selects the desired radio wave, the high frequency amplifier 3 amplifies it, the R and F tuning circuit 4 selects the desired wave, and the mixer 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, and an intermediate frequency transformer 7 extracts only the intermediate frequency signal, and this is sent to the intermediate frequency transformer 7. The frequency amplifier 8 amplifies the signal, and the FM detector 9 converts it into a PM multiplied intermediate frequency audio signal. In the case of stereo broadcasting, a stereo demodulator 10
This audio signal is separated into a right channel and a left channel, each amplified by a low frequency power amplifier 11, and then sent to speakers 12R and 12J.

is driven and played as sound. The A()C circuit 13 is
The intermediate frequency output of the mixer 6 is detected, and the gain of the high frequency amplifier 3 is controlled by outputting a DC voltage 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 input level of the mixer 6 (hereinafter referred to as MIX input) increases in accordance with the antenna input until the antenna signal input level (hereinafter referred to as antenna input) reaches 11.

When the antenna input is larger than 11, A, OC circuit 13
As a result, the MIX input becomes constant. However, when the antenna input becomes larger than 12, it exceeds the control range of the AGC circuit 13, and the A, GC circuit 13
It becomes impossible to control the X human power, and as the antenna input increases again, Ml and the X input increase. Mochi is a huge mix
Distortion occurs in the signal due to the input, and this distortion indicates the limit level that can be confirmed by sound as a low frequency signal after FM detection. That is, when an M I

As described above, the conventional circuit has the drawback that when there is an antenna input that exceeds the control range of the A, OC 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 human power level of the antenna signal, and when it exceeds a predetermined level, automatically activates an attenuation circuit to reduce interference caused by large input interference waves. It is something.

First Embodiment An embodiment of the present invention will now be described in detail with reference to FIGS. 3 to 5. Note that in FIG. 3, the same parts as in FIG. 1 are given the same numbers. In FIG. 3, 111 is a control circuit that compares the output voltage of the A, 0-C circuit 13 with a predetermined value and generates a corresponding control signal, and 15 is controlled by a control signal output from the control circuit 14. It is an automatic attenuation circuit.

FIG. 5 shows the relationship between the antenna input level and the output voltage of the AGC circuit 13. Here, A, G C circuit 13
The vertical axis represents the DC output voltage, and the horizontal axis represents the antenna input level. Figure 4 d: Shows the control circuit 14 and automatic attenuation circuit 15 in Figure 3. In FIG. 4, 20 is an antenna input terminal r-, 21 and 27 are DC blocking capacitors, and 23 and 24 are switching diodes 1' and 2.
2. 25 is a resistor for setting the attenuation amount, 26 is a resistor for DC bias, 28 is an output terminal of the automatic attenuation circuit, 2
9 is a high frequency blocking coil, 30, 31id Bino (Sconten "l-theal").

The above elements 20 to 3] constitute the automatic attenuation circuit 15.

32 is a dryer for driving an automatic attenuation circuit, 33 is an operational amplifier (hereinafter referred to as an operational amplifier), 34.35°37.3
8 is a resistor for setting the switching level, 36 is an NPN type transistor, 39 is an input terminal to which the output voltage of A, GC circuit] 3 is applied, 40 is a power supply terminal, 41 is an output terminal of the operational amplifier 33, 42 is the reference voltage input terminal.

Next, the operation of the above embodiment will be explained. In FIG. 5, when the antenna input level becomes larger than (2), the automatic attenuation circuit 15 applies a predetermined amount of attenuation. With the insertion of the automatic attenuation circuit 15, the AGC circuit output voltage is shifted in parallel toward the antenna input level by the above-mentioned attenuation amount, as indicated by the dot-dashed line in FIG. Next, when the antenna input level becomes less than 18, the attenuation amount is made zero. ■, and 1
A predetermined amount of hysteresis is defined as the difference in level from 8.

At this time, the output voltages of the automatic attenuation circuit 15 in FIG.
The operation of the 1-share circuit 14 will be explained. The output of the driver 32 for driving the automatic attenuation circuit and the output of the operational amplifier 3:3 have opposite polarities, and for example, OV and 8V each output a DC voltage. Attenuation 11'r of automatic attenuation circuit 15
, is zero, the output of the dryer 32 is iJ, 8 to l, and the output of the operational amplifier 33 is OV. When the above conditions are met,
In terms of direct current, the switching diode 23 is biased in the forward direction, and current flows from the driver output to the operational amplifier (32 to 41) through the resistor 26. In addition, resistance 2
It is also divided into 2. At this time, the switching diode 24
is reverse biased. Under this condition, the signal that also enters the antenna input terminal 20 is transmitted to the output terminal 28 of the automatic attenuation circuit 15 with almost no attenuation. Next, dry
When the output of the operational amplifier 32 is OV and the output of the operational amplifier 33 is 8, the switching diode 23 is reversed and the resistor 25. Diode 24° Resistor 22. A current flows in the order of the coil 29. Note that the current is also shunted to resistor 2G. At this time, the signal input from the antenna input terminal 20 is transmitted to the output terminal 28 of the automatic attenuation circuit 15 after being attenuated by the amount determined by the resistor 22 and the resistor 25 . Next, the operation of control circuit]4 will be explained.

The output of the operational amplifier 33 is determined by the magnitude of the mutual voltages at its two input terminals. That is, negative input terminal 3
Regarding the voltages at the two input terminals, 9 and the positive input terminal 42, if the voltage at the input terminal 39 is higher than the input terminal 42, the output of this operational amplifier 33 will be approximately OV, and in the opposite case, the output will be approximately 8 It constitutes a filter.

In this control circuit 14, the switching input voltage of the automatic attenuation circuit 15 is expressed by the following equation, assuming that the insertion level is the main level and the reverse off level.

Wow<tv-! ,, -1-Vcc v,. =-
-(+++(,,-1-IL2) where, ■Mo, is the resistance value of the resistor 37, R2 is the resistance value of the resistor 3B, ■(,3 is the resistance value of the resistor 34, ■t4 is the resistance value of the resistor 3
5, Vcc is the voltage applied to the power supply terminal 40,
() indicates the maximum output DC voltage of the operational amplifier 33 and the DC operating voltage between the base and emitter of the transistor 36 in VB.Here, when the voltage applied to the input terminal 39 is lower than the ON level, the automatic Attenuation circuit 1
5 works, and a predetermined amount of attenuation is obtained. At this time, the output voltage of the operational amplifier 33 is switched from approximately OV to approximately 8V. Next, when the A()C circuit voltage becomes higher than the off level, the automatic attenuation circuit 15 is switched and the amount of attenuation becomes approximately zero. In this way, the antenna power level can be set in correspondence with the on/off level of the circuit output voltage.

Omuro 1fNi-tai II IF I (Hate-kun) Antenna input level disaster: When it gets low, the attenuator is automatically activated to obtain a predetermined amount of attenuation of the input signal level. It has the advantage of reducing distortion. A resistor 25 is added to keep the matching with the antenna tuning circuit constant even when the automatic attenuation circuit is activated, eliminating the negative effect of the automatic attenuation circuit on selectivity. has advantages.

Effects of the Invention The present invention has the above-described configuration, and provides the following effects.

(a) Since the attenuation circuit is activated at the antenna input terminal when the antenna power level is above a predetermined value, distortion can be reduced when the antenna input is large.

(1) Even when the attenuation circuit is activated, it has the advantage of not affecting the selectivity of the antenna tuning circuit because it is a circuit that can be matched with the antenna tuning circuit at the subsequent stage.

[Brief explanation of drawings]

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 same 1.0M radio receiver and the human power level of the mixer, and Fig. 3 is a diagram of the conventional FM radio receiver. A block diagram of a Ji″M radio receiver in one embodiment,
Figure 4 is an electrical circuit diagram of the main parts of the FM radio receiver, and Figure 5 is the antenna input level and AG of the FM radio receiver.
It is a figure which shows the relationship with C circuit output voltage. 1...-antenna, 2...-antenna tuning circuit, 3...
・High frequency amplifier circuit, 4-11. , F tuning circuit, 5 local oscillator, 6 mixer, 7 intermediate frequency transformer, 8
- Intermediate frequency amplifier, 9J/'M detector, 10... Stereo demodulator, 11 Low frequency power amplifier, 1211. ．． 12
L speaker, 13-4 GC circuit, 14/control circuit, 1
5 Automatic attenuation circuit, 20・Antenna input terminal, 21...
Capacitor, 22 - Resistor, 23.24 Switching diode, 25', 26 - Resistor, 27 - Capacitor, 28 Output terminal, 29 - High frequency blocking coil,
30.31 Bypass capacitor, 32...driver,
33 ・Operation amplifier (op-amp) 34. 35... Resistor, 36... Transistor, 37° 38 Resistor, 39
・Input terminal, 40 ・Power terminal, 41 Output terminal, 4
2 Reference voltage input terminal.

Claims (1)

[Claims] A first switching diode connected to a signal transmission path, a first resistor connected in parallel to the first switching diode, and a signal applied to the first switching diode through the first resistor. an antenna tuning circuit that amplifies the output of the antenna tuning circuit, an AGC circuit that generates a DC voltage according to the antenna electric field level and controls the gain of the high frequency amplifier circuit, and an output of the AGC circuit. a comparison means for comparing the voltage with a predetermined value and outputting an open side 1 signal depending on the magnitude; a polarity conversion means for changing the polarity of the control signal output from the comparison means; a second switching diode connected in series with one end of the first switching diode, and a second resistor; and a second switching diode connected in parallel to the series circuit of the second switching diode and the second resistor. 3, and the output of the polarity converting means is applied to the other end of the first switching diode.