JPH05291858A - Compressor circuit - Google Patents

Abstract

PURPOSE:To progress the circuit integration by devising an excellent sine wave to be obtained without use of an IDC circuit while reducing the number of externally mounted capacitors. CONSTITUTION:The compressor circuit in which an output of a gain control circuit 20 is fed back to the gain control circuit via a rectifier circuit 21 to compress a level of a transmission signal is provided with a comparator 26 receiving an output of the rectifier circuit 21 and comparing it with a reference voltage and with an automatic level control circuit 22 controlling the variable gain of the gain control circuit 20 based on an output of the comparator 26. Thus, a sine wave output is obtained independently of an IDC circuit. Furthermore, the comparator 26 uses a diode for setting of the reference voltage and the temperature characteristic is matched with a rectifier diode D3.

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, an IC (integrated circuit) compressor circuit 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 (Instantane) that prevents excessive modulation.
ous Deviation Control) circuit 3, LP
An F (low pass filter) 4 is connected. Further, 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 an FM-modulated audio signal is transmitted.

FIG. 5 shows a detailed circuit in the compressor circuit 2, which is a feedback circuit for controlling the gain by the output of the rectifier circuit. That is, first, the input terminal 8 is connected to the adder 9 via the capacitor C1 and the resistor R1.
This adder 9 is connected to the (inverting) negative-phase input terminal side.
A positive phase voltage is applied from the power supply 10 to the positive phase input terminal of
At the subsequent stage of the adder 9, the output terminal 11 is connected via the capacitor C2. Resistors R2, R3 and a capacitor C3 are provided in parallel between the input and output of the adder 9 (between the negative feedback input and the output), whereby DC (direct current) feedback is applied and AC (alternating current) gain is set. To be 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 a rectifier circuit 14 are connected to the rectifier circuit 14
Has a capacitor C6. In this circuit, all are integrated into an IC except capacitors C1 to C6 (external components). When the IDC circuit 3 is incorporated in the compressor circuit 2 as described above, two diodes D1 whose directions are opposite to each other are provided between the input and output of the adder 9 as the IDC circuit 3, as shown in the figure. The diode clamp circuit consisting of D2 will be connected in parallel.

According to the above circuit configuration, the microphone 1
The audio signal output from the compressor is compressed by the compressor circuit 2 and is suppressed by the IDC circuit 3 so as not to be excessively modulated. As a result, as shown in FIG.
As shown in the compressor characteristic 101 of the above, for example, a decibel output voltage of about 1/2 times the input voltage, that is, −20
The input voltage (VIN) of dB is compressed to the output voltage (VOUT) of about -10 dB. But in this case the ID
By passing through the C circuit 3, as shown in FIG.
Large AC signals are square wave because they are DC clamped by the diodes. Therefore, the LPF 4 removes this harmonic component and converts it into a sine wave signal. After that, in the confidential circuit 5, the voice signal is subjected to modulation processing or the like for preventing wiretapping, and finally, the transmission side FM modulator 6 frequency-modulates and transmits.

On the other hand, in the compander, an expander is used in the receiving circuit, and the received signal is expanded by this expander. For example, in the case of FIG.
By obtaining an output voltage of decibel which is 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 described above, the LPF 4 removes the harmonic component of the signal that has been converted into a square wave by the IDC circuit 3 as described above. This is not always sufficient, and there is a problem in that the sound quality is degraded. Moreover, if an inversion type confidential circuit is connected as the latter confidential circuit 5, the sound quality is further deteriorated.

Further, the IDC circuit 3 composed of the above diode clamp circuit has a problem that it is easily affected by a temperature change. In addition, the IDC circuit 3 has a voltage difference of about 1.4V (0.7V for one diode) due to the two diodes D1 and D2, so that the maximum value of the amplitude limit is fixed. Therefore, there is also a problem that it becomes difficult to adjust the level between the preceding and succeeding circuits.

Therefore, the applicant has proposed to compress the transmission signal by 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.
The ALC circuit 17 is connected to the front stage of 6, but at this time, the ALC circuit 17 also has a rectifier circuit,
A rectifier circuit 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. This capacitor C7, C8
Since it becomes an external component when integrated into an IC, a terminal pin is required, which hinders the integration into an IC.

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

[0011]

In order to achieve the above object, the present invention provides an output of a gain control circuit to a rectifier circuit, and feeds back the output of the rectifier circuit to the gain control circuit to transmit a transmission signal. A compressor circuit for compressing a level has a comparator that inputs the output of the rectifier circuit and compares it with a reference voltage, and controls the variable gain of the gain control circuit based on the output of the comparator to perform automatic level control. The control circuit is provided.
Further, in the above, a diode is used for setting the reference voltage to the comparator in the automatic level control circuit.

[0012]

According to the above structure, the output of the rectifier circuit provided in the compressor circuit is supplied to the comparator, which compares the output of the rectifier circuit with the reference voltage set by the constant current circuit and the diode, for example. Was
The variable gain of the gain control circuit is controlled based on the comparison output. Therefore, the rectification circuit in the compressor circuit can be used to configure the automatic level control circuit, and the compressor circuit incorporating the automatic level control circuit can execute the shift control without using the IDC circuit.

[0013]

FIG. 1 shows the configuration of a compressor circuit according to an embodiment. This compressor circuit is a control which is a part of a gain control circuit 20, a rectifier circuit 21 and an ALC (automatic level control) circuit. It is composed of a circuit 22. In the gain control circuit 20, the adder 9 is connected to the input terminal 8 via the capacitor C1 and the resistor R1 as in the conventional case, and the positive phase voltage from the power source 10 is applied to the positive phase input terminal of the adder 9. The output terminal 11 is connected to the subsequent stage of the adder 9 via the capacitor C2. This adder 9
Between the input and output (between the negative feedback input and output) of the resistors R2 and R in order to apply DC feedback and set the AC gain.
3 and 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 (reverse phase input terminal) of the adder 9 and the output. Further, the gain cell 23 is provided with a gain controlling transistor Q1 between it and the ground.

In the rectifier circuit 21, the adder 9 is added.
Capacitor C5 and resistor R to input the output signal of
5 and an operating circuit 24 are connected to the operating circuit 24. A capacitor C6 and a resistor R6 are connected in parallel with the ground, and a diode D3 as a rectifying element is connected in series to the resistor R6. 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 for the gain control circuit 20.
Supply to. In such a circuit, the input terminal 8
When the voltage VIN is supplied to the
OUT can be obtained at the output terminal 11.

[0016]

[Formula 1] VOUT _(rms) = (I1 · R4 · R5 / R1 · VIN _(av) ) ^1/2 · VIN _(rms) where I1: 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 the constant current circuit 27 and the ground are provided. A diode D4 is connected in series between the input terminal and the output terminal, and the voltage on the anode side of the diode D4 is applied to the comparator 26 as a reference voltage. In addition, this comparator 26
A transistor Q2 for current amplification is provided in the latter stage,
The collector of the transistor Q2 is connected to the contact point 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 mathematical formula 2.

[0018]

EQUATION 2 IALC = VOUT / R5 where VOUT is the 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 the constant current circuit 30 as shown in the figure. And this transistor Q
The output side of the rectification circuit 21 is connected to the base of 3, and the diode D5 is connected to the collector side to the 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. Then, the anode side voltage of the diode D5 is applied to the base of the transistor Q5, and when the output from the rectifier circuit 21 is larger 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 to the transistor Q3 from the rectifier circuit 21, the collector current of the transistor Q3 becomes small and the transistor Q5. Works off. On the other hand, the existence of the constant current circuit 30 causes the collector current of the transistor Q4 to increase 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
Then, the current amplified by the current amplification action flows between the collector and the emitter, and this transistor Q
The amplified current signal 2 is supplied to the gain control circuit 20 as a gain control signal.

The embodiment is constructed as described above, and the audio signal voltage obtained by the microphone is input to the input terminal 8 shown in FIG.
Is input as VIN 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 once. Therefore, the output of the adder 9 is the operating circuit 24, the capacitor C6, the resistor R6.
And the diode D3 which is a rectifying element, and the rectified output is supplied to the comparator 26. In this comparator 26, as shown in FIG. 2, the reference voltage set by applying IALC of the constant current circuit 27 to the diode D4 and the output voltage of the rectifier circuit 21 are compared. In the embodiment, since the diode D4 is used to set the reference voltage of the comparator 26 as described above, it can be adapted to the temperature characteristic of the diode D3 as the rectifying element, and the characteristic variation due to the temperature change can be prevented. It will be possible.

In this way, the control circuit 22 constitutes an automatic level control circuit including the gain control circuit 20 and the rectifier circuit 21, and the current corresponding 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 the transistor Q5 of FIG. 2 causes the comparator 26 to operate and send the gain control signal to the gain control circuit 20 only when the output voltage of the rectifier circuit 21 is higher than the reference voltage. To give. Then, 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 becomes large, the output of the compressor circuit is output. Is controlled in a suppressing direction.

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. , By this, the output of the compressor circuit is the above formula 1.
The output is controlled by the calculation of.

Further, as shown in FIG. 3, the external capacitors in the ALC compressor 28 of the above embodiment are the input capacitor C1 and the output capacitor C2.
Since the capacitor C3 of the adder 9 and the capacitor C6 which is a rectifying element are used, the rectifying capacitor C7 and the coupling capacitor C8 of the conventional ALC circuit 17 are unnecessary as compared with the conventional example of FIG.

In the above embodiment, the diode D4 is used to set 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 for feeding back the output of the rectifier circuit to the gain control circuit, and providing a control circuit having a comparator for inputting the output of the rectifier circuit and comparing it with a reference voltage, and based on the output of the comparator, a variable gain of the gain control circuit. Since an automatic level control circuit for controlling L is formed, the conventional IDC circuit is not used, and L
It is possible to obtain a sine wave output without requiring a PF. Therefore, since the diode clamp circuit is not used as the IDC circuit, the maximum value of the IDC voltage is not fixed, and there is an advantage that the level can be easily adjusted in relation to the circuit at the preceding stage or the latter stage.

Since the rectifier circuit provided in the conventional automatic level control circuit is replaced with the rectifier circuit in the compressor circuit, it is possible to reduce the number of external capacitors. As a result, it is possible to reduce the number of terminals of the IC chip and promote the IC integration.

Further, if the reference voltage source is composed of a diode, the temperature characteristics of the diode serving as a rectifying element will match, and the deterioration of the characteristics due to temperature changes can be improved.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing a configuration in a comparator of the embodiment of FIG.

FIG. 3 is a diagram showing a configuration of an external capacitor of the compressor circuit of the embodiment.

FIG. 4 is a circuit block diagram showing a configuration of a transmission portion of a conventional cordless horn or the like.

FIG. 5 Conventional compressor circuit (including IDC circuit)
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 diagram 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)

[Claims] 1. A compressor circuit for supplying the 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, the input of the rectifier circuit being input. And a reference voltage, and a control circuit for controlling the variable gain of the gain control circuit based on the output of the comparator to perform automatic level control. 2. The compressor circuit according to claim 1, wherein a diode is used to set a reference voltage to the comparator in the control circuit.