JPH0462207B2 - - Google Patents

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 PROBLEMS Figure 1 shows a well-known nonlinear circuit, where the input V _IN
If is less than E ₀ +V _F (V _F is the ON voltage of diode D), the output V _OUT is the same as the input, and the input/output characteristic becomes a straight line with a slope of 1 as shown in FIG. input
When V _IN exceeds E _O +V _F , diode D is turned on and the input/output characteristics become a straight line with a slope of R ₂ /R ₁ +R ₂ (<1).

It is difficult to continuously control the input/output gain characteristics (slope) of the nonlinear portion with the circuit shown in FIG.

Purpose 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 nonlinear circuit of the present invention includes amplifier circuits 1 and 1 that obtain an output signal V _OUT by controlling the amplitude of an input signal V _IN .
0 and 11, gain control circuits 3 and 15 that supply gain control output i given from the outside, and the input signal and a predetermined reference level.
Comparing circuits 2 and 14 are provided for comparing the gain control output with V _r and turning on and off the gain control output based on this reference level. The gain of the amplifier circuit is variably controlled in an input signal region where the gain control output is turned on. As a result, the input/output characteristics of the amplifier circuit exhibit nonlinearity with a breaking point at the reference level, and in the input region on at least one side of the reference level,
The gain of the amplifier circuit can be controlled by an external signal (gain control signal).

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

FIG. 3 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. In FIG. 3, an input signal V _IN passes through a differential amplifier 1 consisting of transistors Q1 and Q2 and is derived as a linear output V _OUT . Transistor pair Q1, Q that constitutes this differential amplifier 1
The emitters of No. 2 are connected through resistors R4 and R5 (R4=R5), and a current source QI (current value I ₁ ) is coupled to the connection point. The output is taken out from one end of a load resistor R3 at the collector of one transistor Q2 whose base is fixed to the reference voltage _VR . Therefore, the input/output gain (slope) of this differential amplifier 1 is R3/2×R4 as shown in FIG.

The input signal V _IN is also applied to the base of one of the transistor pair Q5, Q6. These transistors Q5 and Q6 constitute a comparator circuit 2 (or a clip circuit), and the emitters of each transistor Q5 and Q6 are connected via diodes D1 and D2 and a resistor R6, and the coupling between the diode D1 and the resistor R6 A current source Q7 (current I ₂ ) is connected to the point.

Since the base of one transistor Q6 of this comparison circuit 2 is fixed to the reference voltage _VR , when the input signal V _IN is higher than _VR (V _IN ≧ _VR ), the transistor Q6 is cut off. In other words, inputs greater than V _R are clipped. When V _IN falls below VR (V _IN <V _{R )} , transistor Q6 conducts.
A signal voltage approximately equal to the input V _IN is generated at the emitter of transistor Q5, and the base of transistor Q6 is fixed at a constant voltage _VR , so V _IN /R
A signal current i of 6 flows through resistor R6, and approximately the same current flows through the collector of Q6.

This signal current i is the gain control amplifier 3
The gain control output is derived from the summing point 4 connected to the output of the differential amplifier 1 as a gain control output through the transistor Q.
2 in the collector resistor R3. Through this addition, a voltage output whose amplitude is expanded is obtained from the addition point 4 for inputs that are lower than the reference voltage V _R . Therefore, the input/output characteristics of the circuit in Figure 3 have a slope of 1 in the input region below V _R as shown in Figure 4.
The above becomes a group of straight lines.

The gain control amplifier 3 is composed of a differential amplifier consisting of a pair of transistors Q3 and Q4, and the signal current i flowing out from the common emitter is between Q3 and Q4.
4 and in a controlled ratio. This diversion ratio corresponds to the variable gain of the gain control amplifier 3. The gain control signal is provided via a pair of control lines 5 and 6 in the form of a differential signal.

When the gain is controlled to the maximum, the transistor Q4 of the gain control amplifier 3 is almost conductive, and almost all of the output current i of the comparator circuit 2 is connected to Q4.
It flows through the load resistor R3 of the differential amplifier 1 through the summing point 4. Therefore, the voltage gain of the addition signal at one end of R3 in this state is given by R3/R6. Also, the gain of differential amplifier 1 is as described above.
It is R3/2×R4. Therefore, the maximum voltage gain of the superimposed signal at one end of the load resistor R3 (collector of Q2) is R3/2×R4+R3/R6 (for example, 1+1=2), and the slope corresponding to this gain is expressed as shown in Figure 4. The straight line q _nax that has this becomes the input/output characteristic for the input region below V _R .

When the gain control amplifier 3 is controlled to the minimum gain, the transistor Q3 is conductive.
Q4 becomes non-conductive. Therefore, the signal current i is Q3
The gain of the signal that is diverted to the summing point 4 and added to the addition point 4 becomes zero. That is, as shown by the straight line q ₀ in FIG. 4, no nonlinear amplitude expansion is performed. Input V _IN
The input/output characteristics over the entire range are linear.

Note that the emitters of the transistor pair Q5 and Q6 constituting the comparison circuit 2 (clip circuit) are coupled to each other by a resistor R6 via diodes D1 and D2.
As is well known, these diodes D1 and D2 do not change from off to on (or from on to off) with a steep rise or fall, and have an exponential transition region. Therefore, sudden clipping does not occur above the reference level E _r , and soft clipping is performed in a region with a certain width near the threshold level. As a result,
The bending point of the nonlinear characteristic as shown in Figure 4 is eliminated, and a smooth curved nonlinear characteristic as shown by the dotted line r is obtained, and the adverse effects of nonlinear processing of the amplitude axis of the input signal are reduced. Ru.

Next, FIG. 5 is a circuit showing an application example of the nonlinear circuit shown in FIG. 3, and FIG. 6 is a waveform diagram showing its operation. This circuit is applied to a black expansion circuit for video signals, and its purpose is to
The goal is to match the CRT's cutoff level (video signal pedestal) with the video signal's black peak level, thereby reducing the setup portion of the input video signal and achieving stable black reproduction.

The circuit in Fig. 5 is almost the same as that in Fig. 3, and the reference voltage E _r is applied to the input of the differential amplifier 1 as shown in Fig. 6A.
A video signal whose pedestal level is DC offset by α is given. α is, for example, 50
% white level, and in comparator circuit 2 of Fig. 5, a black signal below the reference voltage E _r (diagonal lines in Fig. 6 A)
is extracted. This black signal passes through the gain control amplifier 3 and is added to the output of the input differential amplifier 1 at the addition point 4, and the black signal is expanded as shown in the shaded area in FIG. 6B. Due to this expansion, the gain of the gain control amplifier 3 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 3 to control the expansion gain as shown in the non-linear portion of FIG. Ru. This black extension control may be feedback control based on the result of black extension.

In FIG. 5, transistors Q5 and Q6 are made inoperative during 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 2. That is, the blanking pulse BLK is applied to the control transistor Q8, and during the synchronization signal period (blanking period), this transistor Q8 is turned on and the current source transistor Q7 is turned off. As a result, the transistor pair Q5 and Q6 constituting the comparator 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 10 consisting of a transistor pair Q15, Q16 and a differential amplifier 1 consisting of transistors Q12, Q13 coupled to its output.
1 constitutes a well-known gain control amplifier. The output of the differential amplifier 10 is converted into a signal voltage of opposite phase to each other at the emitters of a pair of transistors Q11 and Q14 whose bases are fixed at a constant voltage, and is applied to the differential amplifier 11 as a differential input. The output signal taken out from the load resistance R _L of one transistor Q13 of this differential amplifier 11
The gain G of V _OUT with respect to the input signal V _IN is G=V _OUT /V _IN =I ₁ /I ₂・R _L /2R _E , and the current ratio of the emitter current sources 12 and 13 of each differential amplifier 10 and 11 is It is possible to control the gain G by I ₁ /I ₂ .

The input signal V _IN is supplied to one transistor Q17 of the comparator circuit 14 consisting of transistors Q17 and Q18.
It is also given to the base of Since the reference voltage V _R is applied to the base of the other transistor of this comparison circuit 14, when V _IN ≧ V _R , the transistor Q17 is turned on and Q18 is turned off, and the output current of Q17 is changed to the differential amplifier 11. is added as the emitter current. This addition current can be controlled by the magnitude of the common emitter current i of the comparator circuit 14, and this current i is
0 and a current source 16
It can be controlled by the gain control output i of 5. That is, the common emitter current i of the comparator circuit 14 can be controlled by changing the ratio of the current (total I ₃ ) that flows through the transistors Q19 and Q20 even in response to an external control signal, and V _IN ≧V. In the case of _R , this current i is added to the current source I ₁ of the differential amplifier 11 as the output of the transistor Q17. On the other hand, if V _IN < _VR ,
Transistor Q17 is turned off and the input/output gain is fixed.

Therefore, the input/output characteristics of the circuit in Fig. 7 exhibit nonlinear characteristics as shown in Fig. 8, and when V _IN ≧ V _R , the maximum gain
Gain can be controlled within the range of I ₁ + I ₃ /I ₂・R _L /2R _E , minimum gain I ₁ /I ₂・R _L /2R _E , and constant gain I ₁ /I ₂・R when V _R <V _R Fixed to _L /2R _E.

In addition, in FIG. 7, transistors Q17 and Q
By replacing the collector coupling with 18, the gain control region (nonlinear region) of the input/output characteristics becomes the 9th
As shown in the figure, the region is V _IN ≦ _VR .

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. In FIG. 10, the comparator circuit 14
The collector of one transistor Q18 constituting the comparator circuit 1 is connected to one end of the current source 12 of the differential amplifier 10, so that the currents I ₁ and I ₂ of the current sources 13 and 12 are connected to the comparator circuit 1.
It is designed to be controlled by four transistors Q17 and Q18. In order to secure the operating point of transistor Q18, a voltage shifted down from the reference voltage V _R by the voltage of Zener diode ZD2 is applied to the base of Q18, and for balance, a Zener diode is applied to the base of the other transistor Q17. An input voltage V _IN shifted down by the voltage of ZD1 is given.

Therefore, the comparison circuit 14 essentially compares the input signal V _IN and the reference voltage _VR , and if V _IN ≧ _VR , the transistor Q17 is on and Q18 is off.
The gain control current is added to the current I ₁ of the current source 13 of the differential amplifier 11. Therefore, the input/output gain is increased as shown by the solid line in the first quadrant of FIG. Also, if V _IN < _VR , transistor Q1
7 is off and Q18 is on, and the gain control current is added to the current I ₂ of the current source 12 of the differential amplifier 10. Therefore, the input/output gain is reduced as shown by the solid line in the third quadrant of FIG.

The input/output gain is determined by the comparator circuit 14 as in FIG.
It is variably controlled by a control amplifier 15 which controls the common emitter current of. That is, the control amplifier 15 is controlled by the gain control signal.
The current shunting ratio (total I ₃ ) of the transistors Q19 and Q20 constituting the circuit is controlled, and this controlled current becomes the common emitter current of the comparator circuit 14, and one transistor Q1 of the comparator circuit 14
7 or Q18 is turned on in response to the input signal V _IN and is added to the current source I ₁ or I ₂ as a gain control current. The gain of the two-stage gain control circuit consisting of the differential amplifiers 10 and 11 is proportional to I ₁ /I ₂ , so as shown in Figure 11, the gain increases in the input region above V _R and increases in the input region below V _R. A nonlinear characteristic in which the gain decreases in the input region is obtained.

Note that if the connections of the collectors of transistors Q17 and Q18 constituting the comparator circuit 14 are switched in FIG. 10, a variable gain nonlinear characteristic as shown by the dotted line in FIG. 11 can be obtained.

Effects of the Invention According to the present invention, the input/output gain of the amplifier circuit is given a polygonal (non-linear) characteristic in which it changes with the reference level as a boundary by comparing the input signal with the reference level, and furthermore, the input signal on at least one side of the reference level is Since the gain of the amplifier circuit (the slope of the polygonal line) can be variably controlled in the region by an external gain control signal, it can be used as a non-linear variable gain circuit for various signal processing.

[Brief explanation of the drawing]

A circuit diagram of a conventionally well-known nonlinear circuit shown in Fig. 1,
FIG. 2 is an input/output characteristic diagram of FIG. 1, and FIG. 3 is a circuit diagram showing a first embodiment of the nonlinear circuit according to the present invention.
Fig. 4 is an input/output characteristic diagram of Fig. 3, Fig. 5 is a circuit diagram showing an application example of the nonlinear circuit of Fig. 3, and Fig. 6 is a waveform diagram of a video signal showing the operation of the circuit of Fig. 5. , FIG. 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. 9 is a partial modification of the circuit connection of FIG. 7. FIG. 10 is a circuit diagram showing a modification of the nonlinear circuit shown in FIG. 7, and FIG. 11 is an input/output characteristic diagram of FIG. In addition, in the symbols used in the drawings, 1...
... Differential amplifier, 2 ... Comparison circuit, 3 ... Gain control amplifier, 10, 11 ... Differential amplifier,
14...comparison circuit, 15...gain control amplifier.

Claims (1)

[Claims] 1. An amplifier circuit that obtains an output signal by controlling the amplitude of an input signal; a gain control circuit that supplies a gain control output to the amplifier circuit in response to a gain control signal applied from the outside; and the input Compare the signal to a predetermined reference level,
A comparison circuit that turns on and off the gain control output based on the reference level, and variably controls the gain of the amplifier circuit in an input signal region where the gain control output is turned on. straight line circuit.