JP3128473B2 - Radio receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio receiver that performs muting in a weak electric field.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 2, there is known a radio receiver which detects that a received signal has become a weak electric field and mutes a detection signal. In such a radio receiver, the noise level increases when the electric field becomes weak, but the noise level can be suppressed by muting, and a good audibility can be obtained.

In FIG. 2, a received RF signal is converted into an IF signal in a frequency conversion circuit (1). The IF
The signal is amplified by an IF amplifier circuit (2) and detected by a detection circuit (3).
Detected at After that, the output signal of the detection circuit (3) is
Applied to the muting circuit (4). On the other hand, the output signal of the IF amplifier circuit (2) is applied to the electric field strength detection circuit (5), and the electric field strength is detected. Further, the output signal of the IF amplifier circuit (2) is applied to the Hall detection circuit (6),
Hall detection is performed by looking at the level of the amplified IF signal. Thereafter, the output signals of the electric field strength detection circuit (5) and the Hall detection circuit (6) are applied to a muting signal generation circuit (7) and are synthesized. When the electric field becomes weak,
A muting signal is generated from a muting signal generation circuit (7), and the detection signal is muted according to the muting signal.

In general, the output signal of the IF amplifier circuit (2) is applied to an electric field strength detection circuit (5) to detect the electric field strength of a received signal. Therefore, the output signal of the electric field strength detection circuit (5) is as shown in FIG. Further, when the Hall detection circuit (6) detects the IF signal by Hall detection, the output signal of the Hall detection circuit (6) becomes as shown in FIG. And a muting signal generation circuit (7)
Is obtained by inverting and adding the output signal of the electric field strength detection circuit (5) as shown in FIG. 3 (b) and the output signal of the Hall detection circuit (6) as shown in FIG. 3 (c).
A muting signal as shown in (d) is generated. By muting the detection signal in accordance with the muting signal, the received signal level and the noise level change as indicated by the line (a) in FIG. 3A, and the noise is reduced. The line (b) in FIG. 3A shows the change in the received signal level and the noise level when no muting is performed.

[0005]

However, FIG.
(A) Detection circuit when there is no received signal (3)
If the amount of attenuation of the output signal is the no-input mute attenuation,
RF amplifier circuit and IF constituting frequency conversion circuit (1)
There has been a problem that the non-input mute attenuation changes due to variations in the gain of the amplifier circuit (2).
That is, the output signal level of the IF amplifier circuit (2) varies due to the variation in the gain, and the output signal levels of the electric field strength detection circuit (5) and the Hall detection detection circuit (6) are determined by the input signals. The output signal levels of the intensity detection circuit (5) and the Hall detection detection circuit (6) also vary. As a result, the muting signal generation circuit (7) generates a muting signal by simply inverting and adding the output signals of the electric field strength detection circuit (5) and the Hall detection circuit (6). The signal varies due to gain variation. As a result, the muting amount of the muting circuit (4) changes, so that the no-input mute attenuation amount does not become constant.

In addition, in the case of a weak electric field, as shown in FIG. 3A, the noise level changes in accordance with the electric field strength. Had occurred.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and includes a frequency conversion circuit for converting a received RF signal into an IF signal, a detection circuit for detecting the IF signal, and the detection circuit. A muting circuit for muting an output signal of the electric field, an electric field intensity detecting circuit for detecting an electric field intensity according to the IF signal, and a muting for operating the muting circuit according to an output signal of the electric field intensity detecting circuit. A muting signal generation circuit for generating a signal,
And a limiter circuit for limiting the level of the muting signal.

[0008] Further, the voltage dividing circuit includes a voltage dividing circuit for dividing an output signal of the limiter circuit, and a first control circuit for generating a control signal, wherein the voltage dividing circuit has a variable voltage dividing ratio in accordance with the control signal. Features. Further, the first control circuit includes a control terminal to which a resistor is connected, a reference voltage generation circuit that generates a first reference voltage and a second reference voltage lower than the first reference voltage, and a voltage value generated at the control terminal. And the first
And a comparison circuit that compares the second reference voltage with the second reference voltage to generate a control signal.

[0009] Furthermore, a microphone computer for setting a reception state of the radio receiver is provided,
The control circuit comprises a latch circuit for holding an output signal from the microcomputer. Still further, a limit level of the limiter circuit is made variable, and a second control signal for changing the limit level is generated.
And a control circuit.

[0010]

According to the present invention, a received RF signal is converted into an IF signal by a frequency conversion circuit and then detected by a detection circuit. The output signal of the detection circuit is muted by the muting circuit. Further, in the electric field strength detection circuit, the electric field strength is detected according to the IF signal, and when the electric field becomes weak, a muting signal is generated from the muting signal generation circuit. The muting signal is applied to a limiter circuit, and its maximum level is limited. Therefore, the no-input mute attenuation amount can be always kept constant, and the change in the noise level according to the electric field strength at the time of the weak electric field can be made constant.

[0011]

FIG. 1 shows an embodiment of the present invention.
(8) a frequency conversion circuit for converting an RF signal into an IF signal, (9) an IF amplification circuit for amplifying the IF signal,
(10) a detection circuit for detecting the output signal of the IF amplifier circuit (9), (11) a muting circuit for muting the output signal of the IF amplifier circuit (10), (12)
Is a low-frequency amplifier circuit for amplifying the detection output signal, (13) is a speaker driven by the output signal of the low-frequency amplifier circuit (12), and (14) is a received signal according to the output signal of the IF amplifier circuit (9). Electric field strength detection circuit for detecting the electric field strength of
(15) is a Hall detection circuit that performs Hall detection on the output signal of the IF amplifier circuit (9), and (16) is an electric field strength detection circuit (1)
4) and a muting signal generation circuit for generating a muting signal in accordance with an output signal of the Hall detection circuit (15); (17) a limiter circuit for limiting the muting signal level; and (18) a limiter circuit (17). ) Is a voltage dividing circuit for dividing the output signal, and (19) is a control circuit for changing the voltage dividing ratio of the voltage dividing circuit (18).

In FIG. 1, a received RF signal is converted into an IF signal by a frequency conversion circuit (8) and then amplified by an IF amplifier circuit (9). An output signal of the IF amplifier circuit (9) is detected by a detection circuit (10). Detection circuit (10)
After passing through the muting circuit (11),
The signal is amplified by the low frequency amplifier circuit (12), and the speaker (13) is driven by the output signal of the low frequency amplifier circuit (12).

On the other hand, the output signal of the IF amplifier (9) is
Electric field strength detection circuit (14) and Hall detection circuit (15)
Is applied to In the electric field strength detection circuit (14), I
The electric field strength of the received signal is detected in accordance with the output signal of the F amplifier circuit (9),
An output signal corresponding to the electric field strength as shown in (b) is generated. Further, in the Hall detection circuit (15), the output signal of the IF amplification circuit (9) is subjected to Hall detection, and an output signal whose level decreases when a weak electric field is generated as shown in FIG. The output signals of the electric field strength detection circuit (14) and the Hall detection circuit (15) are added after being inverted by the muting signal generation circuit (16), respectively. By such processing,
A muting signal as indicated by a dotted line in FIG. 3D is generated from the muting signal generation circuit (16). The muting signal is applied to a limiter circuit (17), and the maximum value of the muting signal level is limited to a predetermined value V1 as shown by the solid line in FIG. Furthermore, a limiter circuit (1
The output signal of 7) is divided by the voltage dividing circuit (18), and the output signal of the voltage dividing circuit (18) is applied to the muting circuit (11). Then, the amount of attenuation of the muting circuit (18) is determined according to the output signal of the voltage dividing circuit (18).

Thus, the maximum level of the muting signal is limited, so that the levels of the received signal and noise generated from the muting circuit (7) change as shown in FIG. Here, since the maximum level of the muting signal is limited by the operation of the limiter circuit (17), the attenuation of the muting circuit (11) during a weak electric field is constant. Therefore, the gain of the RF amplifier circuit and the IF amplifier circuit (9) constituting the frequency conversion circuit (8) varies, and even if the muting signal level varies, the mute attenuation at the time of no input is kept constant. be able to. Further, it is possible to reduce a noise change according to a change in the electric field strength at the time of a weak electric field. However, the limiter level of the limiter circuit (17) is set to a level that is not affected by the variation in the muting signal level,
The muting circuit (11) is set so that the maximum attenuation is obtained at the limiter level.

The control circuit (1) is connected to the voltage dividing circuit (18).
The control signal generated from 9) is applied, and the voltage dividing ratio of the voltage dividing circuit (18) is changed according to the control signal. Therefore, the output signal level of the voltage dividing circuit (18) changes due to the operation of the voltage dividing circuit (18), and the maximum attenuation of the muting circuit (11) is changed according to the voltage dividing ratio.
Therefore, since the no-input mute attenuation is determined according to the destination, the voltage division ratio can be changed only by changing the control signal from the control circuit (19), and the radio receiver according to the destination can be easily formed. Can be configured.

FIG. 4 shows the voltage dividing circuit (18) of FIG.
(20a) to (20c) are voltage dividing resistors for dividing the output signal of the limiter circuit (17), and (21a) and (21b) are voltage dividing resistors (20b). ) And (20c) are connected to one end of a switching transistor, (22a) to (22c) are resistors for generating reference voltages Vr1 and Vr2, (2c)
3) and (24) are resistors for generating voltages to be compared, and (25) and (26) are reference voltages Vr1 and Vr2.
Are applied to the first and second comparison circuits. The components other than the resistor (24) are integrated into an IC on the same substrate.
Becomes an external resistor of the IC. If the resistance values of the resistors (22a) to (22c) are all set to R, the reference voltage Vr1 applied to the negative input terminal of the first comparison circuit (25) becomes 2 · Vcc / 3 (Vcc: power supply Voltage), and the reference voltage Vr2 applied to the positive input terminal of the second comparison circuit (26) becomes Vcc / 3.

In such a state, the external terminals (2
When an external resistor (24) having a resistance value equal to the resistance value of the resistor (23) is connected as shown in FIG. 7), the voltage value at the positive input terminal of the first and second comparison circuits (25) and (26) Is Vc
c / 2. Therefore, the output signal of the first comparison circuit (25) becomes "L" level, and the output signal of the second comparison circuit (26) becomes "H" level. The first and second comparison circuits (2
The output signals of 5) and (26) are transistors (21a)
And (21b), the transistor (21a) is turned off, and the transistor (21b) is turned on. Therefore, the output signal of the limiter circuit (17) is applied to the muting circuit (11) after being divided by the voltage dividing resistors (20a) and (20c).

When the external terminal (27) is grounded,
Since the output signals of the first and second comparison circuits (25) and (26) are both at "L" level, the transistor (21)
Both a) and (21b) are turned off. Therefore, the output signal of the limiter circuit (17) is directly applied to the muting circuit (11). Further, when the external terminal (27) is opened, the first and second comparison circuits (25) and (2)
Since the power supply voltage Vcc is applied to the positive input terminal of 6),
The output signals of the first and second comparison circuits (25) and (26) both become "H" level, and both the transistors (21a) and (21b) turn on. Therefore, the output signal of the limiter circuit (17) is divided by the resistors (20a) to (20c) and then applied to the muting circuit (11).

Therefore, it is possible to change the voltage division ratio only by changing the connection method of the external resistor (24) to the external terminal (27), and therefore, a radio receiver that can easily correspond to the destination is provided. Can be provided. FIG. 5 shows another specific configuration example of FIG. 4. (28) is a microcomputer for setting the reception state of the radio receiver, and (29a) and (29b) are digital signals from the microcomputer (28). This is a latch circuit for holding data. The microphone computer (28) is, for example,
This is for controlling the reception tuning frequency of the frequency conversion circuit (8).

In FIG. 5, the microcomputer (2)
The digital data generated from the latch circuit (29)
a) and (29b), the latch circuit (29a)
And (29b) generate an "H" or "L" level output signal. Then, the transistors (21a) and (21
b) is turned on or off according to the output signals of the latch circuits (29a) and (29b), and the voltage dividing resistors (20a) to (2a)
0c) changes the partial pressure ratio.

The digital data according to the destination is preset in the microcomputer (28). When the power is turned on, the digital data is stored in the latch circuit (29).
a) and (29b), and the output signals determine the voltage dividing ratio of the voltage dividing resistors (20a) to (20c). Then, the no-input mute attenuation amount can be set according to the destination.

As described above, the microcomputer (2)
By using 8), the circuit can be made into an IC, and it is not necessary to add an external element. FIG. 6 shows another embodiment of the present invention, in which (30) is a limiter circuit capable of changing a limiter level, and (31) is a second control circuit for changing the limiter level. By changing the control signal according to the destination, the limiter level is changed, and the no-input mute attenuation is changed according to the destination. At this time, even if the limiter level is changed, the change in the electric field strength of the muting signal is always the same, so that the change in the muting characteristic according to the change in the limiter level can be eliminated.

[0023]

As described above, according to the present invention, the maximum level of the muting signal is limited to a predetermined value.
The maximum attenuation of the muting circuit is constant, and regardless of the variation in the gain of the RF amplifier circuit and the IF amplifier circuit,
The non-input mute attenuation can be kept constant.

Further, at the time of a weak electric field, the noise level becomes constant in accordance with the electric field strength, so that a sense of incongruity in hearing can be reduced particularly in an in-vehicle radio receiver in which the electric field strength changes frequently. Furthermore, since the output signal of the limiter circuit is divided by the voltage dividing circuit, if the voltage dividing ratio is set according to the destination, the specification can be easily adapted to the destination. When the voltage division ratio is set, it can be set depending on whether or not a resistor is connected, so that a radio receiver suitable for IC integration can be set.

Furthermore, since the voltage division ratio is set by using a microcomputer, a radio receiver suitable for IC integration can be provided. Furthermore, if the maximum mute attenuation is adjusted by changing the limiter level of the limiter circuit, the muting characteristic can be made constant regardless of the change in the limiter level.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional example.

FIG. 3 is a characteristic diagram for explaining the operation of the present invention.

FIG. 4 is a circuit diagram showing a specific configuration example of a main part of the present invention.

FIG. 5 is a circuit diagram showing another specific configuration example of a main part of the present invention.

FIG. 6 is a block diagram showing another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 8 frequency conversion circuit 9 IF amplification circuit 10 detection circuit 11 muting circuit 12 low frequency amplification circuit 13 speaker 14 electric field strength detection circuit 15 level detection circuit 16 muting signal generation circuit 17 limiter circuit 18, 30 voltage dividing circuit 19 first control Circuit 25 First comparison circuit 26 Second comparison circuit 28 Microcomputer 29a, 29b Latch circuit 31 Second control circuit

Claims (5)

(57) [Claims] A frequency conversion circuit for converting a received RF signal into an IF signal; a detection circuit for detecting the IF signal; a muting circuit for muting an output signal of the detection circuit; and an electric field according to the IF signal. An electric field intensity detection circuit for detecting the intensity; a muting signal generation circuit for generating a muting signal for operating the muting circuit in accordance with an output signal of the electric field intensity detection circuit; and a level of the muting signal. A radio receiver, comprising: a limiting limiter circuit; 2. A voltage dividing circuit for dividing an output signal of a limiter circuit, and a first control circuit for generating a control signal, wherein the voltage dividing circuit has a variable voltage dividing ratio according to the control signal. The radio receiver according to claim 1, wherein: 3. The control circuit according to claim 1, wherein the first control circuit includes a control terminal to which a resistor is connected, a reference voltage generation circuit that generates a first reference voltage and a second reference voltage lower than the first reference voltage. 3. The radio receiver according to claim 2, further comprising: a comparison circuit that compares the first voltage value with the first reference voltage and generates a control signal. 4. A microphone computer for setting a receiving state of the radio receiver, wherein the first control circuit comprises a latch circuit for holding an output signal from the microcomputer. 2. The radio receiver according to 2. 5. The radio receiver according to claim 1, further comprising: a second control circuit that changes a limit level of the limiter circuit and generates a control signal for changing the limit level.