JPS6054509A - Nonlinear circuit - Google Patents

Abstract

PURPOSE:To obtain a nonlinear circuit where the inclination of nonlinear characteristics can be controlled with an external signal, by switching the gain of an amplifier with the output of a comparing circuit. CONSTITUTION:When an input signal VIN is higher than a reference voltage VR, a transistor TRQ6 of a comparing circuit 2 is in the cutoff state, and the gain of an amplifier 1 is R3/2R4 if R4=R5 is true. Meanwhile, when the input signal VIN is lower than the voltage VR, the TRQ6 of the comparing circuit 2 is made conductive, and a signal current (i) equal to VIN/R6 is flowed to a resistance R6. This current (i) is shunt to TRs Q3 and Q4 in a gain control amplifier 3 by a gain control signal. Thus, the gain of the amplifier 1 is controlled between R3/2R4+R3/R6 and R3/2R4 and has characteristics shown in a figure. At this time, a smooth curve indicated by a dotted line (r) is obtained by diodes D1 and D2.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a nonlinear circuit whose input/output characteristics exhibit nonlinearity and in which the input/output gain of the nonlinear portion can be controlled.

Background technology and its problems FIG. 1 shows a well-known nonlinear circuit in which the input VIN is E.

If it is less than +VP (V, , is the on-voltage of diode D), the output vou'r is the same as the input, and the input/output characteristics are the second
As shown in the figure, it is a direct expansion with a slope of 1. Input VIN is E.

When +■ is exceeded, the diode D is turned on, and the input/output characteristic has a slope of □ (direct of <1)]H+R2 line.

Input/output gain characteristics (slope) in the non-linear part of the circuit shown in Figure 1
Continuous control is the axis of rotation.

OBJECTS OF THE INVENTION The present invention proposes a nonlinear circuit that can control the slope of nonlinear characteristics using an external signal.

Summary of the Invention The non-linear circuit of the present invention is an amplifier circuit capable of controlling the amplitude of an input signal (V, N) (a differential amplifier (1) in the embodiment of FIG. 6 or a differential amplifier (1) in the embodiment of FIG. 7). Motion 7 mph (lυ
(corresponding to 121). The gain of this amplifier circuit is controlled by the output of a comparison circuit (corresponding to the comparison circuit (2) in FIG. 6 or the comparison circuit in FIG. 7).

This comparison circuit compares the input signal level (■□N) and the reference level (E, ), and outputs an output that can change the gain of the amplifier circuit from the first gain to the second gain with the reference level as the boundary. occurs.

As a result, the input/output characteristics of the amplifier circuit exhibit nonlinearity having a turning point at the reference level.

The output of this comparison circuit is controlled by a control circuit (corresponding to gain control amplifier (3) in FIG. 6 or gain control amplifier a9 in FIG. 7) according to a gain control signal applied from the outside. As a result, the slope of at least one of the straight lines constituting the curve of the nonlinear characteristic is arbitrarily variably controlled by an external gain control signal.

Example The present invention will be explained below based on examples.

FIG. 6 is a circuit diagram showing a first embodiment of a nonlinear circuit to which the present invention is applied, and FIG. 4 is an input/output characteristic diagram thereof. Third
In the figure, the input signal MIN passes through a differential amplifier fi+ consisting of transistors Q1 and Q2, and a linear output V
. It is derived as UT. Transistor pair Q configuring this differential amplifier il+ 1. The emitter of Q2 is connected through resistors R4 and R5 (approximately 4=R, 5), and a current source Q I (current value I,) is coupled to the connection point. The output is taken out from one end of the load resistor R3 at the collector of one transistor Q2 whose base is fixed at the reference voltage 8. Therefore, the input/output gain (slope) of this differential amplifier (1) becomes □ as shown in FIG.

2 ×R4 Human power signal ■N is one of the transistor pair Q5, Q6 (Q
5) is also given to the base. These transistors Q
5. Q6 constitutes a comparator circuit (2) (or a clip circuit), and the emitters of each transistor Q5 and Q6 are connected via diodes DI, D2 and resistor R6, and are connected to the connection point between diode D1 and resistor R6. is the current source Q7 (current I
,) are connected.

Since the base of one transistor Q6 of this comparison circuit (2) is fixed to the reference voltage VR, the input signal WIN
When is smaller than ■1 (■□NnvR), transistor Q6 is cut off. That is, ■. Any input above will be clipped. When VIN falls below VR (VxN〈
VR), transistor Q6 conducts.

A signal voltage approximately equal to the input WIN is generated at the emitter of the transistor Q5, and the base of the transistor Q6 is fixed at a constant voltage (8), so the signal current i of (XN/R6) flows through the resistor (6), and this Approximately the same current flows into the collector of Q6.

This signal current i passes through the gain control amplifier (3) and is derived from the summing point (4) connected to the output of the differential amplifier (1). Current addition with (in phase with) takes place in the resistor 11.3 of the collector of the transistor Q2.

As a result of this addition, a voltage output whose amplitude is expanded is obtained from the addition point (4) for inputs that are equal to or lower than the reference voltage VR. Therefore, the input/output characteristics of the circuit in Figure 6 are as shown in Figure 4.
In the input region below R, a group of straight lines with a slope of 1 or more is formed.

Gain control amplifier (3) is transistor pair Q3
, Q4, the signal stream i flowing out from its common emitter is divided into Q5 and Q4 in a controlled ratio. This shunt ratio corresponds to the variable gain of the gain control amplifier (31).The gain control signal is transmitted in the form of a differential signal to a pair of control lines (51f
61.

In the state where the gain is controlled to the maximum, the transistor Q4 of the gain control amplifier (31) is almost conductive, and the output current i of the comparator circuit (2) is all Q4, and the summing point (4)
It flows through the load resistor 6 of the differential amplifier (1). Therefore, the voltage gain of the addition signal at one end of R3 in this state is given by R3/R6.

In addition, the gain of the differential amplifier (II) is <-7□4 as mentioned above. Therefore, the maximum voltage gain i of the superimposed signal at one end (collector of Q2) of the load resistor I (, 3) and (for example, 1 + 1 = 2), and the direct qmaX with a slope corresponding to this gain as shown in Fig. 4 is
is the input/output characteristic for the following input area.

When the gain control amplifier (3) is controlled to the minimum gain, the transistor Q6 is conductive and the heel Q4 is non-conductive. Therefore, the signal current i is shunted to Q6, and the gain of the signal added to the addition point 141 becomes zero. That is,
Straight line q in Figure 4. As shown in , there is no nonlinear amplitude expansion at all. The input/output characteristics for the entire input VIN range are direct! (lJ near).

Note that the emitters of the transistor pair Q5 and Q6 forming the comparison circuit (2) (clip circuit) f:s are diodes DI,
It is coupled via resistor R6 via D2.

As is well known, the stiff diodes DI and D2 do not change sharply from off to on (or from on to off) with a steep rise or fall, and have an exponential transition region. Therefore, there is no sudden ripping occurring above the reference level Er, and soft clipping is performed in a region with a width near the threshold level. As a result, the bending point that the nonlinear characteristic had as shown in Figure 4 disappears, and a smooth curved nonlinear characteristic as shown by the dotted line r is obtained, which eliminates the negative effects caused by nonlinear processing of the input signal's axis. I think the pillars will be reduced.

Next, FIG. 5 shows a circuit showing an application example of the nonlinear circuit shown in FIG. 6, and FIG. 6 is a waveform diagram showing its operation.

This circuit is applied to a video signal black expansion circuit, and its purpose is to match the cutoff level of the CRT (video signal pedestal) with the black peak level of the video signal. The goal is to reduce the setup part of the video signal and achieve stable black reproduction.

The circuit in Figure 5 is almost the same as that in Figure 3, and the differential amplifier (11
As shown in FIG. 6A, a video signal in which the pedestal level is DC offset by α with respect to the reference voltage Er is applied to the input. α is, for example, a 50 white level, and the comparator circuit (2) in FIG. 5 extracts a black signal (shaded in FIG. 6A) below the reference voltage E. This black signal passes through the gain control amplifier (3) and the addition point (4).
) is added to the output of the input differential amplifier (1;
The black signal is expanded as shown in the diagonal section of FIG. 6B. Through this expansion, the gain of the gain control amplifier 13) is controlled so that the black peak coincides with the pedestal. The gain control signal is given, for example, as the output of a comparator that compares the black peak hold value and the pedestal level, and this control signal is given to the gain control amplifier (31) to adjust the expansion gain in the nonlinear portion of Fig. 4. This black extension control is controlled as follows.
It may be feedback control based on the result of black extension.

In FIG. 5, transistors Q5 and Q6 are made inoperative in the sync signal portion so that the sync signal extending below the pedestal level is not detected as a black signal by the comparator circuit 12). That is, the blanking pulse BLK is applied to the control transistor Q8, and the transistor Q8 is
is turned on, and current source transistor Q7 is turned off. As a result, the transistor pair Q5 and Q6 constituting the comparison circuit (2) is turned off, and the black detection operation is prohibited.

Next, FIG. 7 is a circuit diagram showing another embodiment of the nonlinear circuit of the present invention, and FIG. 8 is its input/output characteristic diagram. In Fig. 7, a differential amplifier 0 consisting of transistor pair Ql 5 and Ql 6 is shown.
ω and transistors Q12, Ql coupled to its output
3 differential amplifiers (Ill constitutes a well-known gain control amplifier) The output of the differential amplifier aω is a pair of transistors Q11 whose bases are fixed at a constant voltage,
The signal voltages are converted into signal voltages having mutually opposite phases at the respective emitters of Ql 4, and are applied as differential inputs to a differential amplifier. One transistor Q13 of this differential amplifier ttn
The gain G of the output signal voUT taken out from the load resistor RL with respect to the input signal VIN is , and the emitter current source (+
It is possible to control the gain G by the current ratio 1/2 of 21.03).

The input signal VIN is also applied to the base of one transistor Q17 of the comparator circuit (14+) consisting of transistors Q17 and Ql8.The base 4 voltage vn is applied to the base of the transistor on the iln side of this comparator circuit 04. Therefore, when VIN≧VB, transistor Q17 is on and Ql8 is off, and the output current of Q17 is added as the emitter current of differential amplifier Uυ. This addition current can be controlled by the magnitude of the common emitter current i of the comparator circuit (1 (a)), and this current i is controlled by a control amplifier (5) consisting of a transistor pair Ql9, Q20 and a current source (161). In other words, the transistors Q19 and Q19 can be controlled by an external control signal.
By changing the ratio of the current (total I) that is shunted through Q20, the common emitter current i of the comparator circuit α (a)
can be controlled, and in the case of VIN≧■, this current i is sent to the differential amplifier U as the output of the transistor Q17.
It is added to the current source ■1 of υ. On the other hand,■! When N<Vl, transistor Q17 is turned off and the input/output gain is fixed.

Therefore, the input/output characteristics of the circuit in Figure 7 are similar to those in Figure 8.
In the figure, if the collector connections of transistors Q17 and Ql8 are swapped, the gain control region of the input/output characteristics (
The nonlinear region) is a region where VIN≦vR as shown in FIG.

Next, FIG. 10 shows a modification of the nonlinear circuit shown in FIG. 7, and FIG. 11 shows the input/output characteristics of the circuit shown in FIG. m
In Fig. 10, the collector of one transistor Q18 constituting the comparator circuit (141) is connected to one end jc of the current source (121) of the differential amplifier Uflll, and the current source 1131
The transistors Q17 and Ql8 of the comparator circuit f141 control the transistors Q17 and Ql8 of the comparator circuit f141. In order to ensure the operating point of transistor Q18, a normal voltage shifted down from the reference voltage V□ by the voltage of Zener diode ZD2 is applied to the base of transistor Q18, and for balance, the other transistor Q1
The base of 7 is given an input 1; 1-voltage voltage N which is shifted down by the voltage of the Zener diode ZDI.

Therefore, the comparator circuit Q41 compares the input signal vIN with the torque VR at the time t1, and if %VIN≧vFL, the first. In this case, transistor Q17 is on and Ql8 is off, and the gain control current is connected to the current source (13+) of differential amplifier U.
is added to the current I. Therefore, the input/output gain is the first
It is increased as shown by the solid line in the first quadrant of FIG.

Also, if N<VR, transistor Q17 is off and Ql8 is on, and the gain control current is changed to the differential amplifier a [
is added to the current source (12+ current source).

Therefore, the input/output gain is reduced as shown by the solid line in the third quadrant of FIG.

The input/output gain is variably controlled by the control amplifier a9 which controls the common emitter current of the comparator circuit α(a) as in FIG. That is, the current shunt ratio of transistors Q19 and Q20 (total I3) that constitutes the control amplifier (19) is determined by the gain control signal.
is controlled, this controlled current becomes the common emitter current of the comparator circuit α4, one transistor Q17 or Ql8 on the comparator circuit side is turned on according to the input signal VIN, and the current source 1 or the current source 1 is output as a gain control current. It is added to 2. The gain of the two-stage gain control circuit consisting of the differential amplifier GOIIIυ is proportional to 11/I2, so as shown in Figure 11, the gain increases in the input range of 78 or higher and decreases in the input range of VR or lower. By switching the collector connections of transistors Ql 7 and Ql 8 that constitute comparison circuit a (a) in Fig. 10, a nonlinear characteristic with a variable gain as shown by the dotted line in Fig. 11 can be obtained. It will be done.

Effects of the Invention As described above, the present invention compares the level of the input signal with the reference level, and based on the comparison result, the input/output gain of the circuit σ] is configured to change with the reference level as the border, and By controlling the above comparison result output using an external gain control signal and variably controlling the input/output gain,
Foldable bag 0> The bag is configured to change the inclination of at least one side. With this configuration, it is possible to obtain a very useful integrated linear circuit in which the slope of the nonlinear characteristic can be arbitrarily and variably controlled from the outside.

4. Brief explanation of the drawings 0 Fig. 1 is a circuit diagram of a conventionally well-known nonlinear circuit, Fig. 2 is an input/output characteristic diagram of Fig. 1, and Fig. 6 is a circuit diagram of a nonlinear circuit according to the present invention. 4 is the input/output characteristic diagram of FIG. 3, FIG. 5 is a circuit diagram showing an application example of the nonlinear circuit of FIG. 6, and FIG. 6 is the circuit of FIG. 5. 7 is a circuit diagram showing a second embodiment of the non-linear circuit according to the present invention, FIG. 8 is an input/output characteristic diagram of FIG. 7, and FIG. Fig. 10 is a circuit diagram showing a modified example of the nonlinear circuit shown in Fig. 7, and Fig. 11 is a human output characteristic diagram when the wiring of the circuit shown in Fig. 10 is partially changed. .

In addition, in the symbols used in the drawings, (11...
・・・・・・・・・・・・Differential up (2)・・・・・・
・・・・・・Comparison circuit (3)・・・Song...
...Kane Control Amplifier Scream [11]...
・・・・・・Differential amplifier■・・・・・・・・・・・・
...At the time of comparison circuit......Gain control amplifier agent Masaru Dotsu〃 Yoshio Tsuneko〃 Toshiki Sugiura

Claims (1)

[Claims] An amplifier circuit that can control the amplitude of the input signal compares the level of the input signal with a predetermined reference level, and changes the gain of the amplifier circuit from the first gain to the second gain with this reference level as a boundary. The output of the comparison circuit is controlled in accordance with an externally applied gain control signal, and the output of the comparison circuit is controlled in accordance with an input signal region on at least one side of the reference level. A non-linear circuit comprising a controller circuit that variably controls the gain of an amplifier circuit.