JP2569391B2 - Compressor circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compressor circuit, and more particularly to a circuit for signal compression used in cordless horns, transceivers and the like.

[0002]

2. Description of the Related Art Conventionally, in a compander such as a low power cordless horn or a transceiver, a compressor circuit formed as an integrated circuit (IC) has been used to compress a transmission signal. FIG. 4 shows an outline of a transmission circuit of a cordless horn as an example. A compressor circuit 2 is connected to a microphone 1, and the compressor circuit 2 has an IDC (Instantanee) for preventing excessive modulation.
ous Deviation Control-Instantaneous Deviation Control) Circuit 3, LP
An F (low-pass filter) 4 is connected. A transmission-side FM modulator (frequency modulator) 6 is connected to the LPF 4 via a secret circuit 5 for preventing eavesdropping and the like, and transmits an FM-modulated audio signal.

FIG. 5 shows a detailed circuit in the compressor circuit 2, and this circuit is a feedback circuit for controlling the gain by the output of a rectifier circuit. That is, first, the input terminal 8 is connected to the adder 9 via the capacitor C1 and the resistor R1.
(Inverting type) connected to the negative-phase input terminal side,
Is supplied with a positive-phase voltage from the power supply 10,
The output terminal 11 is connected via the capacitor C2 at the subsequent stage of the adder 9. Between the input and output of the adder 9 (between the negative feedback input and the output), resistors R2 and R3 and a capacitor C3 are provided in parallel, whereby DC (direct current) feedback is applied and AC (alternating current) gain is set. Is done.

A gain cell 12, a resistor R4 and a capacitor C4 are connected in parallel between the input and output of the adder 9, and the output signal of the adder 9 is input to output a control signal to the gain cell 12. Capacitor C5, resistor R5
And the rectifier circuit 14 is connected.
Has a capacitor C6. In this circuit, all of the circuits except for the capacitors C1 to C6 (external components) are implemented as ICs. When the IDC circuit 3 is incorporated in such a compressor circuit 2, as shown, two diodes D1 having opposite directions are provided between the input and output of the adder 9 as the IDC circuit 3, as shown in FIG. A diode clamp circuit composed of D2 is connected in parallel.

According to the above circuit configuration, the microphone 1
6 is compressed by the compressor circuit 2 and suppressed by the IDC circuit 3 so that excessive modulation is not applied. As a result, FIG.
As shown in the compressor characteristic 101, for example, an output voltage of about 1/2 times the input voltage in decibels, that is, -20
The dB input voltage (VIN) is compressed to an output voltage (VOUT) of about -10 dB. However, in this case the ID
By passing through the C circuit 3, as shown in FIG.
Large AC signals are square waves because they are DC clamped by diodes. Therefore, the LPF 4 removes this harmonic component and converts it into a sine wave signal. Thereafter, the privacy signal circuit 5 performs a modulation process or the like on the audio signal for eavesdropping prevention, and finally performs frequency modulation on the transmission-side FM modulator 6 and transmits the signal.

On the other hand, in a compander, an expander is used in a receiving circuit, and a received signal is expanded by the expander. For example, in the case of FIG.
By obtaining an output voltage of about twice the input voltage as shown in the expander characteristic 102, the input audio signal of the compressor circuit 2 is reproduced as 1: 1 as shown in the characteristic 103.

[0007]

However, in the compressor circuit 2, the LPF 4 removes the harmonic component of the square wave signal by the IDC circuit 3 as described above. This is not always sufficient, and there is a problem that the sound quality is reduced. In addition, when an inverted privacy circuit is connected as the privacy circuit 5 at the subsequent stage, the sound quality is further deteriorated.

Further, the IDC circuit 3 including the diode clamp circuit has a problem that it is easily affected by a temperature change. In addition, since the IDC circuit 3 has a voltage difference of about 1.4 V (0.7 V for one diode) between the two diodes D1 and D2, the maximum value of the amplitude limit is fixed. Therefore, there is also a problem that it is difficult to perform level adjustment with a circuit in a preceding stage or a subsequent stage.

Therefore, the present applicant has proposed to compress the transmission signal using an ALC (automatic level control) circuit. In this case, since the IDC circuit 3 is not used, a sine wave signal is generated. There is an advantage that it can be obtained. However, in this case, there are the following problems. That is, in this case, as shown in FIG.
6, the ALC circuit 17 is connected to the preceding stage. In this case, the ALC circuit 17 also has a rectifier circuit,
A rectifier capacitor C7 is required. Also, ALC
A DC coupling capacitor C8 is required at the connection between the circuit 17 and the compressor circuit 16. These capacitors C7 and C8
However, there is a problem in that the IC becomes an external component when it is formed into an IC, so that terminal pins are required, which hinders the formation of the IC.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to obtain a good sine wave without using an IDC circuit and to reduce the number of external capacitors to realize an IC. It is an object of the present invention to provide a compressor circuit capable of promoting the following.

[0011]

In order to achieve the above object, the present invention provides an output of a gain control circuit to a rectifier circuit, feeds back the output of the rectifier circuit to the gain control circuit, A compressor circuit for compressing the level, having a comparator for inputting the output of the rectifier circuit and comparing the input with the reference voltage, and controlling the variable gain of the gain control circuit based on the output of the comparator to perform automatic level control. Is provided.
In the above, a diode is used for setting a reference voltage to a comparator in the automatic level control circuit.

[0012]

According to the above arrangement, the output of the rectifier circuit provided in the compressor circuit is supplied to the comparator, and the comparator compares the output of the rectifier circuit with the reference voltage set by, for example, a constant current circuit and a diode. And
The variable gain of the gain control circuit is controlled based on the comparison output. Therefore, an automatic level control circuit can be configured using the rectifier circuit in the compressor circuit, and the compressor circuit incorporating the automatic level control circuit can execute deviation control without using an IDC circuit.

[0013]

FIG. 1 shows a configuration of a compressor circuit according to an embodiment. The compressor circuit includes a gain control circuit 20, a rectifier circuit 21, and a control circuit which is a part of an ALC (automatic level control) circuit. It comprises a circuit 22. In the gain control circuit 20, an adder 9 is connected to an input terminal 8 via a capacitor C1 and a resistor R1 as in the prior art, and a positive-phase voltage from a power supply 10 is applied to a positive-phase input terminal of the adder 9. The output terminal 11 is connected to the subsequent stage of the adder 9 via a capacitor C2. This adder 9
Between input and output (between the negative feedback input and the output) to apply DC feedback and to set the AC gain.
3 and a capacitor C3 are provided in parallel.

A gain cell 23, a resistor R4 and a capacitor C4 are connected in parallel between the negative feedback input (negative phase input terminal) and the output of the adder 9. The gain cell 23 is provided with a transistor Q1 for gain control between the gain cell 23 and the ground.

The adder 9 is provided in the rectifier circuit 21.
, The capacitor C5 and the resistor R
5 and an operating circuit 24, a capacitor C6 and a resistor R6 are connected in parallel between the operating circuit 24 and the ground, and a diode D3 as a rectifier is connected to the resistor R6 in series. The anode side of the diode D3 is connected to the base of the transistor Q1 in the gain control circuit 20, and the output of the rectifier circuit 21 is used as a gain control signal.
To supply. In such a circuit, the input terminal 8
Is supplied with a voltage VIN, a voltage V
OUT can be obtained at the output terminal 11.

[0016]

V OUT _(rms) = (I 1 · R 4 · R 5 / R 1 · VIN _(av) ) ^1/2 · VIN _(rms) where I 1: current of constant current circuit in gain cell, rms:
Effective value, av: Average value.

Further, in the control circuit 22, a comparator 26 for inputting a signal from the anode side of the diode D3 is provided, and a constant current circuit 27 of variable current is provided. And a diode D4 is connected in series between the two and a voltage on the anode side of the diode D4 is supplied to the comparator 26 as a reference voltage. Also, this comparator 26
In the subsequent stage, a transistor Q2 for current amplification is provided.
The collector of the transistor Q2 is connected to the contact between the gain cell 23 in the gain control circuit 20 and the collector of the transistor Q1. The current IAL of the above constant current circuit 27
C is set by the following equation (2).

[0018]

IALC = VOUT / R5 where VOUT is an effective value output voltage.

FIG. 2 shows a detailed circuit in the comparator 26. The comparator 26 has transistors Q3 (input side) and Q4 which are emitter-connected to a constant current circuit 30 as shown. And this transistor Q
The output side of the rectifier circuit 21 is connected to the base of the rectifier circuit 21 and a diode D5 is connected to the collector side between the rectifier circuit 21 and ground. On the other hand, a reference voltage set by the constant current circuit 27 and the diode D4 is applied to the base of the transistor Q4, and the collector of the transistor Q5 is connected to the collector side. The anode of the diode D5 is applied to the base of the transistor Q5. When the output from the rectifier circuit 21 is higher than a predetermined reference voltage, the transistor Q2 is turned on.

According to the comparator 26, when a voltage higher than the reference voltage applied to the base of the transistor Q4 is input from the rectifier circuit 21 to the transistor Q3, the collector current of the transistor Q3 decreases and the transistor Q5 Operates off. On the other hand, due to the presence of the constant current circuit 30, the collector current of the transistor Q4 increases in proportion to the input voltage of the transistor Q3 and becomes the base current of the transistor Q2 (due to the OFF operation of the transistor Q5). Turn on. Therefore, this transistor Q2
In this case, the current amplified by the current amplifying action flows between the collector and the emitter.
2 is supplied to the gain control circuit 20 as a gain control signal.

The embodiment has the above configuration, and the audio signal voltage obtained by the microphone is applied to the input terminal 8 shown in FIG.
Is input as VIN to the gain circuit 23 and once supplied to the gain cell 23 and the operation circuit 24 in the rectifier circuit 21 after passing through the adder 9 in the gain control circuit 20. Therefore, the output of the adder 9 is the operation circuit 24, the capacitor C6, the resistor R6
The rectified output is supplied to a comparator 26. In the comparator 26, as shown in FIG. 2, the reference voltage set by applying IALC of the constant current circuit 27 to the diode D4 is compared with the output voltage of the rectifier circuit 21. In the embodiment, since the diode D4 is used to set the reference voltage of the comparator 26 as described above, the temperature can be matched with the temperature characteristic of the diode D3 as a rectifying element, and the characteristic variation due to a temperature change can be prevented. It becomes possible.

As described above, the control circuit 22 constitutes an automatic level control circuit including the gain control circuit 20 and the rectifier circuit 21, and controls the current according to the voltage difference between the output voltage of the rectifier circuit 21 and the reference voltage. 2 is fed back to the gain control circuit 20, but only when the output voltage of the rectifier circuit 21 is higher than the reference voltage by the transistor Q5 in FIG. To give. In the gain cell 23 in the gain control circuit 20, the voltage applied to the negative-phase input terminal of the adder 9 is controlled by the gain control signal, and when the output of the rectifier circuit 21 increases, the output of the compressor circuit increases. Is controlled in the direction of suppressing.

On the other hand, when the output voltage of the rectifier circuit 21 is smaller than the reference voltage, there is no output from the comparator 26, and the gain cell 23 is controlled by the output of the transistor Q1 operated by the output of the rectifier circuit 21. Thus, the output of the compressor circuit becomes
The output is controlled by the calculation of

As shown in FIG. 3, an external capacitor in the ALC compressor 28 of the above embodiment is composed of a capacitor C1 at an input portion and a capacitor C2 at an output portion.
, The capacitor C3 of the adder 9 and the capacitor C6, which is a rectifying element, eliminate the need for the rectifying capacitor C7 and the coupling capacitor C8 of the conventional ALC circuit 17 as compared with the conventional example of FIG.

In the above embodiment, the diode D4 is used for setting the reference voltage of the comparator 26 in the control circuit 22, but a resistor or a diode-connected transistor or the like can be used instead of the diode D4.

[0026]

As described above, according to the present invention,
A compressor circuit that feeds back the output of the rectifier circuit to the gain control circuit; and a control circuit that has a comparator that receives the output of the rectifier circuit and compares the output with the reference voltage. Is formed without using a conventional IDC circuit.
A sine wave output can be obtained without requiring a PF. Therefore, since the diode clamp circuit is not used as the IDC circuit, there is an advantage that the maximum value of the IDC voltage is not fixed, and the level can be easily adjusted in relation to the previous or subsequent circuit.

Since the rectifier circuit provided in the conventional automatic level control circuit is substituted for the rectifier circuit in the compressor circuit, the number of external capacitors can be reduced. As a result, the number of terminals of the IC chip can be reduced, and IC implementation is promoted.

Furthermore, if the reference voltage source is constituted by a diode, the temperature characteristics of the diode as the rectifying element match, and deterioration of the characteristics due to a temperature change can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a configuration of a compressor circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration inside a comparator of the embodiment of FIG. 1;

FIG. 3 is a diagram illustrating a configuration of an external capacitor of the compressor circuit according to the embodiment.

FIG. 4 is a circuit block diagram showing a configuration of a transmission portion such as a conventional cordless horn.

FIG. 5 shows a conventional compressor circuit (including an IDC circuit).
FIG. 3 is a circuit diagram showing the configuration of FIG.

FIG. 6 is an explanatory diagram showing the operation of the compander.

FIG. 7 is a diagram showing a configuration of an external capacitor when an ALC circuit is added to a compressor circuit in the related art.

FIG. 8 is a waveform chart showing an output signal of the IDC circuit.

[Explanation of symbols]

 2, 16 ... compressor circuit, 3 ... IDC circuit, 9 ... adder, 12, 23 ... gain cell, 14, 21 ... rectifier circuit, 17 ... ALC circuit, 20 ... gain control circuit, 22 ... control circuit, 26 ... comparator, C1 to C8: capacitors, R1 to R6: resistors, D1 to D5: diodes, Q1 to Q5: transistors.

Claims (2)

(57) [Claims] 1. A compressor circuit for supplying an output of a gain control circuit to a rectifier circuit, feeding back the output of the rectifier circuit to the gain control circuit, and compressing the level of a transmission signal. And a control circuit for performing automatic level control by controlling a variable gain of the gain control circuit based on the output of the comparator. 2. The compressor circuit according to claim 1, wherein a diode is used for setting a reference voltage to a comparator in said control circuit.