JPH0648982Y2 - Variable compression ratio compression circuit - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to a compression circuit suitable for noise reduction of communication devices such as mobile phones and audio equipment, and the input / output voltage ratio can be set arbitrarily. The present invention relates to a variable compression ratio type compression circuit.

[Prior art]

As shown in FIG. 3, the conventional compression circuit is mainly composed of an inverting amplification type operational amplifier circuit 3, and a variable gain circuit 4 and a rectifying / smoothing circuit 5 to which an output signal from the operational amplifier circuit 3 is supplied. The output terminal of the variable gain circuit 4 is connected to the inverting input terminal of the operational amplifier circuit 3. 1 is an input terminal, 2 is an output terminal, and C1, C3, and C4 are coupling capacitors. C2 is a bypass capacitor, and 9 is a reference voltage source supplied to the non-inverting input terminal of the operational amplifier circuit 3.

[Problems to be solved by the device]

Such a conventional compression circuit is used in a communication device such as a car telephone, and is a circuit that compresses an input signal to a predetermined level and outputs the compressed signal. The output from the operational amplifier circuit 3 is rectified by the rectifying / smoothing circuit 5, and the gain control current I _G according to the DC level thereof is flown into the variable gain circuit 4 or is drawn to control the gain control circuit 4. There is. And the output current obtained through the variable gain circuit 4.
Whether I _OUT is drawn from the input stage of the operational amplifier circuit 3,
Alternatively, the variable gain circuit 4 adjusts the gain between the input and output terminals of the operational amplifier circuit 3, feeds it back to the operational amplifier circuit 3, compresses the input signal level to a predetermined level, and derives the output signal. It is a thing.

The variable gain circuit 4 is supplied with the output current I _IN from the operational amplifier circuit 3 via the coupling capacitor C3 and the resistor R2, and the gain control current I _G according to the output voltage V _OUT of the operational amplifier circuit 3. Are drawn in or flowed in through the rectifying / smoothing circuit 5. The variable gain circuit 4 draws or flows an output current I _OUT according to the DC level of the gain control current I _G from the inverting input terminal side of the operational amplifier circuit 3 so that the output current I _OUT is between the input and output terminals of the operational amplifier circuit 3. Is a control circuit for controlling the gain of the. The output current I _OUT from the variable gain circuit 4 is expressed by the following equation.

(However, I ₀ is the current value peculiar to the current source of the amplifier forming the variable gain circuit 4, and R ₂ is the resistance value of the resistor R _2. ) The DC current I _G is the operational amplifier. Output voltage V _{OUT of} 3 and resistance
Required by R1.

I _G = V _OUT / R ₁ (2) (However, R ₁ is the resistance value of the resistor R _1. ) The output current I _OUT from the variable gain circuit 4 is Is asked.

I _OUT = V _IN / R ₃ ………… (3) (However, V _IN is the input signal voltage applied to input terminal 1, R
₃ is the resistance value of the resistor R3. ) Therefore, the following equation is obtained from the equations (1), (2) and (3).

Equation (4) is expressed as the following equation when logarithms are taken on both sides.

21ogV _OUT ＝ logV _IN ＋ logK ………… (5) Also, when converting equation (5) in decibels, it is expressed as the following equation.

2 | V _OUT | _dB = | V _IN | _dB + | K | _dB (6) Note that K = I ₀ · R ₁ · R ₂ / R _3, which is an eigenvalue.

As is clear from the equation (6), the input voltage V _IN and the output voltage V
_When I convert the relationship of _OUT to Digibell, the input / output ratio is about 1/2.

The input / output characteristics of such a compression circuit are obtained by feeding back the operational amplifier circuit 3 by the variable gain circuit 4 to obtain a ratio of the output signal level to the input signal level as shown in (b) of FIG. Is set to a fixed value of 1/2. Incidentally, the horizontal axis of FIG. 4 is the input signal level, and the vertical axis is the output signal level. The so-called normal compression circuit input / output characteristics are fixed according to the 1/2 rule. When the compression ratio of the input and output signals is fixed in this way, there is a drawback that it can be used only for limited applications such as car telephones, and there is room for improvement.

The main object of the present invention is to provide a compression circuit which is a simple circuit in which the input / output voltage ratio can be arbitrarily set.

[Means for solving the problem]

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and is to provide an inverting amplification type operational amplifier circuit to which an input signal is input, and to obtain a gain control current by smoothing a DC component from the operational amplifier circuit. Rectifying and smoothing circuit, and a gain control current supplied from the rectifying and smoothing circuit, the gain is controlled, and a variable gain circuit that feeds back to the operational amplifier circuit and a variable current is supplied to the gain control current from the rectifying and smoothing circuit And a variable current source circuit that operates.

[Action]

The compression circuit of the present invention comprises an inverting amplification type operational amplifier circuit to which an input signal is input, and a DC component of the output of the operational amplifier circuit is blocked through a capacitor, and a signal component is a variable gain circuit via a resistor. And a rectifying / smoothing circuit, and a variable current from the variable current source circuit is added to the gain control current supplied to the variable gain circuit from the rectifying / smoothing circuit, and the result is supplied to the variable gain circuit to provide an operational amplifier. Is multiplied by negative feedback to set the input / output voltage ratio to a predetermined compression ratio.

〔Example〕

The compression circuit of the present invention, as shown in FIG.
In addition to the conventional compression circuit shown in the figure, a variable current source circuit 7 that supplies a variable current I ₁ to the gain control current I ₂ from the rectifying / smoothing circuit 5
The addition circuit 6 adds the variable current I ₁ to the gain control current I ₂ and supplies the gain control current I _G to the variable gain circuit 4.

FIG. 2 is a circuit diagram showing a specific example of the compression circuit of the variable compression ratio type according to the present invention.

In the figure, the rectifying / smoothing circuit 5 is applied with an output voltage V _OUT via a resistor R1, and the other end of the resistor R1 is connected to a commonly connected input terminal of an amplifier A2 and an inverting amplifier A3. ,
These output terminals are connected to the bases of the transistors Q5 and Q6, respectively, and the collectors of the transistors Q5 and Q6 are connected to the current mirror circuit 12 to form a full-wave rectifier circuit. The output stage transistor of the current mirror circuit 12 is a smoothing capacitor.
Connected to C5 and resistor R7 and smoothed. The other end of the resistor R7 is connected to the base / collector of the transistor Q4 of the current mirror circuit 13, and the collector of the transistor Q3 at the output stage is connected to the variable gain circuit 4.

The output voltage V _OUT of the operational amplifier 3 is supplied to the variable gain circuit 4 through the resistor R2, and the other end of the resistor R2 is connected to the base and collector of the diode-connected transistor Q7, and the collector of the transistor Q7. Is connected to the inverting input terminal of the operational amplifier A1 and is also connected to the constant current source circuit. The non-inverting input terminal of operational amplifier A1 is the reference voltage source.
10 and its output terminal is connected to the bases of the transistors Q8 and Q9. The base of the transistor Q10 is connected to the reference voltage source 10. Transistor Q9, Q
Ten collectors are connected to the power supply voltage, each connected to a current source circuit. The emitters of the transistors Q9 and Q10 are commonly connected to the transistor Q2 of the variable current source circuit 7 and the collector of the transistor Q3 of the rectifying / smoothing circuit 5. The base of the transistor Q10 is connected to the reference voltage source 10, and the collector of the transistor Q9 is connected to the non-inverting input terminal of the operational amplifier 3 via the resistor R8. The non-inverting input terminal of the operational amplifier A1 is connected to the reference voltage source 10.

Incidentally, 6 is an adder circuit, which is achieved by connecting the collectors of the transistors Q2 and Q3 to each other as shown in FIG.

Further, the variable gain circuit 4, the rectifying / smoothing circuit 5 and the variable current source circuit 7 are not limited to those in the embodiment of FIG.

The operation of the compression ratio variable type compression circuit of the present invention will now be described based on the embodiment of FIG.

Output voltage V _OUT of the operational amplifier 3 is output variable current I ₂ is rectified and smoothed by the rectifying and smoothing circuit 5, the variable current I ₂ is drawn from the variable gain circuit 4 via the current mirror circuit 13. Moreover, the variable current I ₁ is drawn from the variable current source circuit 7 from the variable gain circuit 4. Therefore, the variable current I _G drawn from the variable gain circuit 4 is expressed by the following equation.

I _G = I ₁ + I ₂ ……………… (7) I ₂ = V _OUT / R ₁ ………… (8) Therefore, the variable current _IG is (7) (8) It is expressed as the following equation from the relation of equations.

I _G = I ₁ + V _OUT / R ₁ (9) The output current I _OUT of the variable gain circuit 4 is expressed by the equation (1).
From the expressions (3) and (9), the relationship of the following expression is obtained.

Further, when the equation (10) is expressed in logarithm, it is expressed as logV _OUT + log (V _OUT + I ₁ R ₁ ) = logV _IN + logK …………………… (11). Also, when the equation (11) is converted in decibels, it is expressed as the following equation.

│V _OUT │ _dB ＋ log (V _OUT ＋ I ₁ R ₁ ) ＝ ｜ V _IN ｜ _dB ＋ | K | _dB …………………… (12) (K is K = I ₀ · R ₁ · R ₂ / R ₃ and K is an eigenvalue.) As is clear from the expression (12), the compression ratio of the present invention is the compression ratio of the input voltage V _IN and the output voltage V _OUT is the variable current source circuit. 7
This is done by controlling the variable current I _G by controlling the current I ₁ output from. The input / output terminals of the operational amplifier 3 are controlled by the variable gain circuit 4 and can be adjusted to a desired compression ratio. As shown by the input / output characteristics in FIG. , (1: 1) to the straight line (b) in Fig. 4 as shown in the straight line (b) in Fig. 4.
It is possible to change the compression ratio range shown in (c) of FIG. 4 during (1: 1/2) as shown in FIG.

Further, in the compression circuit of the present invention, as is apparent from the expression (12), if the variable current I ₁ is zero, the compression ratio of the input voltage V _IN and the output voltage V _OUT becomes 1: 1/2, The compression ratio approaches (1: 1) as the variable current I ₁ is increased.

[Effect of device]

The variable compression ratio type compression circuit of the present invention is a compression circuit that can set a desired compression ratio by operating a variable current source circuit with an extremely simple circuit. It is extremely effective as a compression circuit of a noise reduction circuit for applications such as cordless horns.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a variable compression ratio type compression circuit of the present invention, and FIG. 2 is a circuit diagram showing a specific example of a variable compression ratio type compression circuit of the present invention. FIG. 3 is a circuit diagram showing a conventional compression circuit, and FIG. 4 is a diagram for explaining input / output characteristics of the compression ratio variable type compression circuit of the present invention. 3: Operational amplifier circuit, 4: Variable gain circuit, 5: Rectification smoothing circuit, 6: Addition circuit, 7: Variable current source circuit, 9, 10: Reference voltage source, 12, 13: Current mirror circuit,

Claims (1)

[Scope of utility model registration request] 1. An inverting amplification type operational amplifier circuit to which an input signal is input, and an output signal of the operational amplifier circuit is obtained through a capacitor, and the output signal is supplied via first and second resistors, respectively. A variable gain circuit and a rectifying / smoothing circuit, the gain of the variable gain circuit is controlled by a gain control current output from the rectifying / smoothing circuit, and the output of the variable gain circuit is an inverting input of the operational amplifier circuit. In the compression circuit connected to the terminal, the current supplied from the variable current source circuit is added to the gain control current supplied from the rectifying / smoothing circuit to the variable gain circuit, and the gain control current is supplied. The compression ratio variable type compression circuit, wherein the input signal supplied to the operational amplification circuit is output at a desired compression ratio by controlling the gain of the.