JPH0671213B2 - Gain control circuit of receiver - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gain control circuit of a receiving device preferably used for an electronically tuned radio receiver.

2. Description of the Related Art In a radio receiver of the superheterodyne system using a tuning circuit having an electronically variable reactance element such as a variable capacitance diode called a variable cap,
Since the capacitance of the barrier cap changes according to the input signal voltage, distortion may occur depending on the input signal voltage. Occurrence of such distortion is roughly classified into the following two types.

(1) When the received signal itself is distorted In the varicap, the harmonic component increases as the input signal voltage increases. Therefore, in the superheterodyne receiver, due to the accuracy of the local oscillation circuit,
When the received signal has twice the frequency of the intermediate wave signal,
A subtle difference occurs between the intermediate frequency signal between the received signal and the local oscillation signal and the intermediate frequency signal between the second harmonic of the received signal and the local oscillation signal, and a beat sound is generated due to this difference.

(2) When there is distortion other than the received signal When there is a signal (interfering signal) having a frequency near the tuning frequency signal, a harmonic is generated in the interfering signal itself. That is, the input signal voltage of the varicap is V
And the capacitance of the barrier cap when there is no AC signal is C ₀ , the capacitance change of the barrier cap due to the AC signal is Δ
C is Is approximated by. However, a, b, and c are coefficients.

Here, the carrier level is E, the modulation degree is m, the carrier angular frequency is ωct, and the modulation angular frequency is ωmt. When the interference signal is represented by E (1 + mCOSωmt) COSωct (2), From formula 1, It can be expressed as. The underlined portion in the third expression is a direct current component and a low frequency component of the modulated wave of the interference signal, and the received signal is amplitude-modulated by these components, which deteriorates the intermodulation characteristic.

In order to solve the above problems, the gain control of the input signal has been conventionally performed so that the input voltage of the barrier capacitor does not exceed a predetermined value. Generally, when the above two characteristics, that is, the beat characteristic and the intermodulation characteristic are compared, the input signal level allowed for the varicap is smaller than that for improving the beat characteristic due to the required performance and the degree of influence. Need to be kept to. Therefore, in a typical conventional technique, automatic gain control (hereinafter referred to as "AGC") is performed using the configuration shown in FIG.

FIG. 13 is a block diagram showing the electrical configuration of a typical prior art radio receiver 1. In this radio receiver 1, the received signal from the antenna 2 is transmitted from the attenuator 3 and the high frequency amplifier circuit 4 through the line 5 to the tuning circuit 6
Entered in. The tuning circuit 6 has the same frequency characteristic and is composed of a two-stage LC filter including a coil and a barrier cap. The output from the tuning circuit 6 is given to the mixing circuit 8 from the line 7, is mixed with the local oscillation signal from the local oscillation circuit 9, and is output to the line 10 as an intermediate frequency signal. This intermediate frequency signal is given to the detection circuit 16 and demodulated into an acoustic signal, and is sonicated from the speaker 18 via the power amplification circuit 17.

The output from the high frequency amplifier circuit 4 and the output from the tuning circuit 6 are added by the adder circuit 11 and input to the AGC circuit 12. In the AGC circuit 12, the output from the adder circuit 11 is amplified by the amplifier circuit 13 and envelope-detected by the detection circuit 14. The detection circuit 14 generates a duty pulse corresponding to the input signal level, and this pulse is converted into a DC voltage level by the smoothing circuit 15 and given to the attenuator 3 from the line 19.

The attenuator 3 changes the attenuation rate of the received signal from the antenna 2 in response to the input voltage from the line 19 and guides it to the high frequency amplifier circuit 4, whereby the AGC operation is realized. In the radio receiver 1, the AGC operation for improving the cross modulation characteristic is performed based on the output from the high frequency amplifier circuit 4, and the AGC operation for improving the beat characteristic is performed based on the output from the tuning circuit 6.

In the radio receiver 1 configured as described above, the level of the input signal to the tuning circuit 6, that is, the high frequency amplifier circuit 4
The output signal level from the tuning circuit 6 is indicated by reference numeral 1 in FIG. 14, and the output signal level from the tuning circuit 6 is indicated by reference numeral 2 in FIG.
Indicated by.

On the other hand, the level of the disturbing signal applied to the barrier cap is
Due to the characteristics of the first-stage tuning circuit itself, the more it detunes, the more it attenuates. Therefore, when the AGC operation for improving the intermodulation characteristic is performed based on the input signal of the tuning circuit 6 indicated by reference numeral 1 in FIG. 14, even if the interfering signal is detuned, the attenuator 3 The output signal from the device is suppressed to an unnecessarily low level, which suppresses the received signal of the radio broadcast desired to be received, and the audio output may be reduced.

Also, as indicated by reference numeral 3 in FIG.
When the AGC operation is performed based on the output from the first-stage tuning circuit, if the received signal and the interfering signal are close to each other, the output level of the high-frequency amplifier circuit 4 indicated by reference numeral 1 is higher than that of the high-frequency amplifier circuit 4. Since the output level of the first-stage tuning circuit indicated by the reference numeral 3 is a high level, the level suppression operation more than necessary is performed. Therefore, conventionally, as shown in FIG. 13, the AGC operation for improving the intermodulation characteristic is performed based on the output of the high frequency amplifier circuit 4.

An object of the present invention is to prevent unnecessary level suppression operation,
A gain control circuit of a receiver capable of performing an AGC operation with improved intermodulation characteristics and beat characteristics.

Means for Solving the Problems The present invention has a tuning element having nonlinearity with respect to an input signal level, and controls a reception signal level according to an output signal level of a tuning circuit that tunes to a predetermined frequency. In a gain control circuit of a receiver, a first tuning circuit that is tuned to the frequency and has a characteristic as indicated by reference numeral 3 in FIG. 14 and a second tuning to which an output signal of the first tuning circuit is input. A circuit, an output signal of the first tuning circuit having the characteristic indicated by the reference numeral 3 and an output signal of the second tuning circuit having the characteristic indicated by the reference numeral 2 in FIG. 2 and FIG. The first and second levels are adjusted so that the output signal level from the first tuning circuit becomes smaller than the output signal level from the second tuning circuit as indicated by reference numeral 6 in FIG. Adjusting means, adding means for adding the output signals from the first and second level adjusting means to each other to obtain a characteristic as indicated by reference numeral 5, and as the output of the adding means increases. A gain control circuit for lowering the received signal level.

Operation According to the present invention, the received signal is derived from the gain control circuit through the first and second tuning circuits to a subsequent stage, for example, a circuit for converting to an intermediate frequency. The first and second tuning circuits are connected in series and each tunes to a frequency predetermined by the characteristic indicated by reference numeral 3 in FIG. Therefore, the second tuning circuit outputs a reception signal tuned with the characteristics shown by reference numeral 2 in FIG. 14 and reference numeral 4 in FIG. 2 to the circuit in the subsequent stage.

However, the first and second tuning circuits include tuning elements having non-linearity with respect to the input signal level, such as varicaps, and therefore the input signal level is set to a desired value. Gain control operation is required. For this reason, in the present invention, the output signal of the first tuning circuit having the characteristic shown by reference numeral 3 is taken out for improving the intermodulation characteristic, inputted to the first level adjusting means, and as shown by reference numerals 2 and 4. This characteristic is taken out from the output signal of the second tuning circuit for improving the beat characteristic and is input to the second level adjusting means.

In these first and second level adjusting means, the output signal level from the first tuning circuit having the characteristics shown by the reference numeral 3 is output from the second tuning circuit as shown by the reference numerals 2 and 4. The levels are mutually adjusted so that the characteristic indicated by reference numeral 6 which is smaller than the level is obtained. The outputs from the first and second level adjusting means are added to the adding means, and thus the adding means can obtain an output having a characteristic indicated by reference numeral 5. The output from the adding means is given to the gain control means, and the received signal level is lowered as the output of the adding means increases, and thus the gain control is performed.

Therefore, the received signal level can be controlled such that the intermodulation characteristic and the beat characteristic have an optimal gain in harmony with each other without suppressing the received signal more than necessary.

Embodiment FIG. 1 is a block diagram showing the electrical construction of a radio receiver 21 according to an embodiment of the present invention. The received signal received by the antenna 22 is led from the attenuator 23 to the line 20,
It is given to the first tuning circuit 25 via the high frequency amplifier circuit 24. The output from the first tuning circuit 25 is applied to the second tuning circuit 27 via the line 26, and the output from the second tuning circuit 27 is applied to the mixing circuit 29 via the line 28. A local oscillation circuit 30 is provided in association with the mixing circuit 29, and from the mixing circuit 29, the received signal via the line 28 and the local oscillation signal from the local oscillation circuit 30 are mixed to generate an intermediate frequency signal. Derived. This intermediate frequency signal is detected by the detection circuit.
It is demodulated into an acoustic signal at 31 and is sonicated from the speaker 33 via the power amplification circuit 32.

The output from the first tuning circuit 25 is given to one input of an adding circuit 37 via a line 35 and an amplifying circuit 36. The output from the second tuning circuit 27 is given to the other input of the adding circuit 37 from the line 38 through the amplifying circuit 39. The adder circuit 37 gives an output corresponding to the output from the amplifier circuits 36 and 39 to the amplifier circuit 42 of the AGC circuit 41.

The output from the amplifier circuit 42 is envelope-detected by the detection circuit 43, and a duty pulse corresponding to the output from the addition circuit 37 is derived from the detection circuit 43 to the smoothing circuit 44.
The smoothing circuit 44 derives a DC voltage level signal corresponding to the duty of the input pulse signal to the attenuator 23. The AGC circuit 41 configured in this manner increases the attenuation rate of the attenuator 23 as the output from the adder circuit 37 increases, and lowers the reception signal level input to the high frequency amplifier circuit 24.

The first and second tuning circuits 25 and 27 are both
The frequency characteristic shown by reference numeral 3 in the figure is obtained, and the frequency characteristic obtained by combining the first and second tuning circuits 25 and 27 is as shown by reference numeral 2 in FIG. 14 and reference numeral 4 in FIG. Become. Further, the gain of the amplifier circuit 36 is set relatively lower than the gain of the amplifier circuit 39. Therefore, the output signal of the first tuning circuit 25 having the characteristic shown by the reference numeral 3 is As shown by reference numeral 6 in FIG. 2, the output signal of the second tuning circuit 27 shown by the reference numerals 2 and 4 is suppressed to be small.

FIG. 3 shows a high-frequency amplifier circuit 24 and first and second tuning circuits 25 and 27 in the radio receiver 21 having the above-mentioned configuration.
FIG. 6 is an electric circuit diagram when and are realized by a general configuration.
The received signal from the attenuator 23 input from the line 20 is given to the base of the transistor 51 forming the high frequency amplifier circuit 24. The collector of the transistor 51 is connected to the high level power source Vcc through the primary winding 53 of the tuning coil 52, and the emitter is grounded. One terminal of the secondary winding 54 of the tuning coil 52 has a varicap 55.
The first tuning circuit 25 includes the tuning coil 52 and the varicap 55.

The other terminal of the secondary winding 54 of the tuning coil 52 is connected to the line
The primary winding 63 of the tuning coil 62 of the second tuning circuit 27 via 26
It is connected to one of the terminals and is grounded via a coil 57 for coupling the first tuning circuit 25 and the second tuning circuit 27. The line 35 is drawn out from the tap 58 of the secondary winding 54 and connected to the amplifier circuit 36.

The other terminal of the primary winding 63 of the tuning coil 62 is grounded via a varicap 65, and thus the varicap 65 and the tuning coil 62 form a second tuning circuit 27.
The line 38 is drawn out from the tap 68 of the primary winding 63,
It is connected to the amplifier circuit 39. The output from the second tuning circuit 27 is led to the line 28 from the secondary winding 64 of the tuning coil 62.

In the high frequency amplifier circuit 24 and the first and second tuning circuits 25 and 27 shown in FIG. 3, the transmission characteristic of the tuning circuit 25 is shown in FIG. 4 and the phase characteristic is shown in FIG. Similarly, the transmission characteristic of the tuning circuit 27 is shown in FIG. 6, and the phase characteristic is shown in FIG. The graphs shown in FIGS. 4 to 7 are all calculated. These 4th
From the calculation results shown in FIGS. 7 to 7, the transmission characteristics obtained by adding the first and second tuning circuits 25 and 27 are as shown in FIG.

From FIG. 8, the transmission characteristic sharply drops when the tuning frequency exceeds 1 MHz. This means that the output impedance of the first tuning circuit 25 becomes inductive due to the coil 57, whereas the second tuning circuit 27 also becomes inductive at a frequency lower than the tuning frequency and becomes in phase. On the other hand, at a frequency higher than the tuning frequency, the second tuning circuit 27 becomes capacitive and the phase thereof is inverted, and the level of the output derived on the line 35 and the output derived on the line 38 are increased. This is because the relationship causes cancellation. Such a problem occurs at a frequency lower than the tuning frequency when a capacitor is used in place of the coil 57, and the transmission characteristic sharply deteriorates as described above.

However, since the output from either the first or second tuning circuit 25 or 27 is taken as a current instead of a voltage, the phase of this current is shifted by 90 degrees from the phase of the voltage. , The phase difference between the output from the first tuning circuit 25 and the output from the second tuning circuit 27 is within 90 degrees,
It is possible to approach a desired frequency characteristic shown by reference numeral 5 in FIG. 2 which will be described later.

FIG. 9 shows a high frequency amplifier circuit 24 and a first embodiment of the present invention.
3 is an electric circuit diagram of a second tuning circuit 25 and 27. FIG. In FIG. 9, parts corresponding to those in FIG. 3 are designated by the same reference numerals. In the configuration shown in FIG. 9, one terminal of the varicap 55 is connected to one terminal of the secondary winding 54 of the tuning coil 52, and the resonance of the first tuning circuit 25 derived from the other terminal. Current is drawn from transistor 71 through line 72a through resistor 72 for current / voltage conversion.

FIG. 10 is a graph showing the phase characteristic of the resonance current derived from the first tuning circuit 25 to the transistor 71. Therefore, the transmission characteristic of the sum of the output voltage derived from the first tuning circuit 25 to the line 35a and the output voltage derived from the second tuning circuit 27 to the line 38 is as shown in FIG. , AGC, as indicated by reference numeral 5 in FIG. 2 above.
It is possible to obtain a desired characteristic in which the output voltage to the circuit 41 exhibits a sharp rise in the vicinity of the tuning frequency and gradually decreases with detuning.

FIG. 12 is an electric circuit diagram showing a specific configuration of the radio receiver 21 according to the embodiment of the present invention, and the same reference numerals are given to the portions corresponding to the above-mentioned FIG. 1 and FIG. The received signal from the antenna 22 is input to the high frequency amplifier circuit 24 via the line 20 and given to the base of the transistor 51 from the resistor 81. In the first and second tuning circuits 25 and 27, the varicaps 55 and 65 are connected to the line 84 via resistors 82 and 83, respectively.
A tuning bias voltage input from is applied. The connection point between the variable cap 55 and the resistor 82 is a capacitor.
It is connected to one terminal of the secondary winding 54 of the tuning coil 52 via 85, and the connection point of the varicap 65 and the resistor 83 is connected to the other terminal of the primary winding 63 of the tuning coil 62 via the capacitor 86. Connected.

The output from the first tuning circuit 25 is the secondary winding of the tuning coil 52.
The resonance current, which is led to the line 35 via the coil 87 connected to one terminal of 54, and flows in the secondary winding 54 in this way, can be shunted and led to the amplifier circuit 36. The inductance of the coil 87 is determined from the divided flow rate to the amplifier circuit 36, and the inductance of the coil 87 and the tuning coil are determined.
The parallel combined inductance of 52 with the secondary winding 54 is chosen to be equal to the inductance of the primary winding 63 of the tuning coil 62. The coil 57 is the primary winding 63 of the tuning coil 62.
It is selected to be about 1/10 of the inductance of.

The amplifier circuit 36 is composed of a transistor 88, a capacitor 89, and a resistor 90. The output of the first tuning circuit 25 led to the line 35 is a resistor via the capacitor 89.
It is applied to the emitter of transistor 88 which is grounded by 90. The base of this transistor 88 has a line
A bias voltage is applied via 91.

The amplifier circuit 39 includes a transistor 92, a capacitor 93, and a resistor 94. The output from the second tuning circuit 27 input via the line 38 is given to the base of the transistor 92 from the capacitor 93. The bias voltage from the line 91 is also applied to the ace of the transistor 92 via the resistor 95. The emitter of the transistor 92 is grounded via the resistor 94.

The output of the amplifier circuit 36 derived from the collector of the transistor 88 and the output of the amplifier circuit 39 derived from the collector of the transistor 92 are added at the connection point 96, and the amplifier circuit
Entered in 42. It should be noted that the gains of the amplifier circuits 36 and 39, that is, the peak value levels of the characteristic indicated by reference numeral 6 and the characteristic indicated by reference numeral 4 in FIG. It can be set by the tap ratio in 63.

This connection point 96 is also connected to the high level power supply via the resistor 97.
Connected to Vcc. The output of the amplifier circuit 42 is given to the smoothing circuit 44 including the low-pass filter 98 and the amplifier circuit 99 via the detection circuit 43.

The output from the smoothing circuit 44 is input to the attenuator 23 via the resistor 100. The attenuator 23 is a capacitor 101,
102 and diodes 103 and 104 are included,
The DC voltage from the smoothing circuit 44 is applied from the capacitor 101 through the diode 103 to the connection point 105 between one terminal of the capacitor 102 and the anode of the diode 104. The cathode of the diode 104 is grounded and the capacitor 102
The other terminal of is connected to the line 20. Thus, when the DC voltage level derived from the smoothing circuit 44 becomes high,
The diode 104 becomes conductive, the received signal input via the line 20 is bypassed, and the attenuation rate increases.

In the radio receiver 21 configured as described above, the first
By the AGC circuit 41 controlling the attenuation factor of the received signal by the attenuator 23 based on the output current drawn from the tuning circuit 25 to the line 35, the cross modulation characteristic can be improved, and the second tuning circuit 27 The beat characteristic can be improved by controlling the attenuation rate by the attenuator 23 based on the output voltage derived on the line 38. The phase of the output current from the first tuning circuit 25 and the second tuning circuit
The phase of the output voltage from 27 is within a range of ± 90 degrees, and therefore the input voltage of AGC circuit 41 does not have the local dip shown in FIG. 8 and is shown in FIG. It is possible to obtain a desired characteristic shown by the reference numeral 5 in FIG. 2 which has a steep rise near the tuning frequency and gradually decreases with detuning. Further, the gains of the amplifier circuits 36 and 39 can be individually set to optimum values in accordance with the required performance, and the attenuator 23 can prevent the received signal level from being suppressed more than necessary.

As described above, according to the present invention, the reception signal level decreases as the sum of the signal level based on the output of the first tuning circuit and the signal level based on the output of the second tuning circuit increases. The signal based on the output of the first tuning circuit is used as a signal for improving the intermodulation characteristic by making it relatively smaller than the signal based on the output of the second tuning circuit. The signal based on the output of is used as a signal for improving the beat characteristic, so that the received signal is not suppressed more than necessary, and the received signal has an optimal gain in which the intermodulation characteristic and the beat characteristic are harmonized. You can control the level.

[Brief description of drawings]

FIG. 1 is a block diagram showing the electrical configuration of a radio receiver 21 according to an embodiment of the present invention, FIG. 2 is a graph for explaining the AGC operation of the radio receiver 21, and FIG. 3 is a high frequency amplifier circuit 24.
FIG. 4 is a graph showing the transmission characteristic of the first tuning circuit 25 shown in FIG. 3, and FIG. 4 is an electric circuit diagram in the case where the first and second tuning circuits 25 and 27 are realized by a general configuration. FIG. 6 is a graph showing the phase characteristic of the first tuning circuit 25, FIG. 6 is a graph showing the transmission characteristic of the second tuning circuit 27, FIG. 7 is a graph showing the phase characteristic of the second tuning circuit 27, and FIG. The graph shows the transmission characteristics of the first and second tuning circuits 25 and 27 together.
FIG. 9 is an electric circuit diagram showing the actual configuration of the high-frequency amplifier circuit 24 and the first and second tuning circuits 25 and 27 of one embodiment of the present invention, and FIG. 10 is the first tuning shown in FIG. FIG. 11 is a graph showing the phase characteristics of the circuit 25, and FIG. 11 is a graph showing the transmission characteristics of the first and second tuning circuits 25 and 27 shown in FIG.
FIG. 12 is an electric circuit diagram showing a concrete structure of a radio receiver 21 of an embodiment of the present invention, FIG. 13 is a block diagram showing an electric structure of a radio receiver 1 of the prior art, and FIG. 14 is a radio. 6 is a graph for explaining the AGC operation of receivers 1 and 21. 21 ... Radio receiver, 23 ... Attenuator, 24 ... High-frequency amplifier circuit, 25 ... First tuning circuit, 27 ... Second tuning circuit, 29 ... Mixing circuit, 30 ... Local oscillation circuit, 31, 43 ……
Detection circuit, 36,39,42,99 …… Amplification circuit, 37 …… Adding circuit, 41 …… AGC circuit, 44 …… Smoothing circuit, 52,62 …… Tuning coil, 55,65 …… Barrier cap

Claims (1)

[Claims] 1. A gain control circuit of a receiving device, which has a tuning element having nonlinearity with respect to an input signal level, and controls the received signal level in accordance with the output signal level of the tuning circuit which tunes to a predetermined frequency. In the first tuning circuit, the first tuning circuit that tunes to the frequency and the second tuning circuit to which the output signal of the first tuning circuit is input, and the output signals of the first and second tuning circuits are input, respectively. Between the first and second level adjusting means for adjusting the level so that the output signal level from the first tuning circuit becomes smaller than the output signal level from the second tuning circuit, and the output signals from the first and second level adjusting means are mutually And a gain control circuit for reducing the received signal level as the output of the addition circuit increases. .