JPH069327B2 - Gain control circuit - Google Patents

Description

The present invention relates to a gain control circuit, and more particularly to a gain control circuit in a video signal amplification system for a color CRT monitor.

[Prior Art] A variable transconductance type multiplication circuit is conventionally used for gain control (amplitude adjustment) in a video signal amplification system for a color CRT monitor.

As a conventional example related to the present invention, for example, edited by Utsunomiya and Wakui: Image Electronic Circuit, edited by Television Society,
Corona, July 1986, PP 100-109.

[Problems to be Solved by the Invention]

In the variable transconductance type multiplication circuit having only the first quadrant of the above-mentioned prior art, the slope of the output signal with respect to the input signal obtained by the magnitude of the control signal, ie, the gain
It becomes like the figure.

On the other hand, the video signal of the video signal amplification system has a signal waveform peculiar to video in which the amplitude changes to the white level side with respect to the black level as shown in FIG.

Therefore, in FIG. 3, if the reference value (black level) of the video signal is set to V _iB , an offset occurs in the output signal and the reference value of the video signal cannot be determined only by this circuit.

An object of the present invention is to provide a gain control circuit in which the slope of the output signal with respect to the input signal, which is changed depending on the magnitude of the control signal, that is, the gain, intersects at one point at all gains.

[Means for Solving the Problems]

In the variable transconductance type multiplying circuit, one of the outputs of the differential amplifier is taken out in a current form, and the operation of the nonlinear corrector for correcting the nonlinear operation of the input transistor of the differential amplifier in the output current. It is achieved by adding a current linked to the current.

[Action]

Extracting and adding the current linked to the operating current of the non-linear correction unit to the output current of the differential amplifier unit adds a bias amount to the slope of the output signal with respect to the input signal set by the control signal, that is, the gain. If this bias amount is obtained as an amount that is inversely proportional to the control signal, a large amount is biased when the gain is small and a small amount is biased when the gain is large, so that all the gains are constant. As a result, the reference value of the video signal can be made constant, so that no offset occurs in the output signal.

〔Example〕

A specific embodiment to which the present invention is applied will be described below with reference to FIG.

In FIG. 1, 1 is an input terminal, 2 is a control terminal, 3 is an output terminal, 4 is a power supply voltage terminal, 100 is a differential amplifier, and 20
Reference numeral 0 is a non-linear correction unit, and reference numeral 300 is a current-voltage conversion unit.
The differential amplifier 100 is a variable transconductance type multiplication circuit, and includes transistors Q ₁ , Q ₂ , Q ₃ , and Q ₆ and a resistor R _{E. The} transistors Q ₁ , Q _{2 form} a differential pair, and The input terminal 1 is connected to the base of Q ₆ . Non-linear correction unit 200 transistor _Q 7 to Q
₁₁ and a resistor R1 and constant current sources CC1 and CC2. The control terminal 2 is provided at the base of the transistor Q ₇ , the reference voltage source Vr is provided at the base of the transistor Q ₈ , and the bases of the transistors Q ₉ and Q ₁₀ are provided. Bias power supply V _B is connected. Current - voltage converter 300 becomes transistors _Q 4, _{Q 5} a resistor _{R 2,} the transistors _Q 4, Q
Each of the emitters ₅ is connected to the output terminal 3.
The bases of the transistors Q ₁ and Q ₂ of the differential amplifier 100 are the transistors Q ₉ and Q _{10 of the} non-linear correction unit 200, respectively.
Connected to the Emitter. The transistor Q ₃ of the differential amplifier 100 and the transistor Q of the current-voltage converter 300
₄ has a current mirror configuration. In addition, the transistor Q ₁₁ and the current-voltage conversion unit 3 of the nonlinear correction unit 200
The transistor Q _{5 of} 00 also has a current mirror configuration,
This current mirror is for applying a bias current.

The operation of FIG. 1 in the above configuration will be described. First, the operation when no bias current is applied except for the current mirror configuration of the transistors Q ₁₁ and Q ₅ will be described.

In the differential amplifier 100, the collector currents of the transistors Q ₁ and Q ₂ are I ₁ and I ₂ , the input signal applied to the input terminal 1 is V _i , the base / emitter voltage of the transistor Q ₆ is V _BE , and the resistor R. _When the value of _E is R _E , the current I ₁ + I _{2 which} is the sum of the collector currents flowing in the transistors Q ₁ and Q ₂ with respect to the input signal V _i is obtained by (V _i −V _BE ) / R _E. Current ratio of _{I 1} and _{I 2,} the transistor _{Q 1}
Let ΔV be the differential voltage between the bases of Q ₂ and Q ₂ , Can be obtained in a relationship. Here, V _T represents a thermal voltage. As can be seen from the equation (1), the linearity of I ₁ / I ₂ is Δ
V is obtained only in the range of V _T , which is as narrow as about 26 mV.

Therefore, the non-linear correction unit 200 is used to obtain a wide linear operation range. Therefore, transistors Q ₁ and Q ₂
The differential voltage ΔV between the bases of the transistors is generated as a voltage obtained between the emitters of the transistors Q ₉ and Q ₁₀ . That is, Δ
V is the collector currents of the transistors Q ₉ and Q ₁₀ , I _A and I _B , respectively, Can be obtained at. Furthermore, ICC values of the reference signal V _r, a constant current source CC1 CC2 of (2) of the current ratio I _{B /} I _A is a control signal applied to the control terminal 2 V _c, a reference voltage source V _r , And the value of the resistor R ₁ is R ₁ , Can be obtained at. Therefore, substituting equation (2) into equation (1), And the exponential current operation of the differential amplifier 100 can be linearized by the logarithmic conversion of the non-linear correction unit 200.
Moreover, the current ratio I ₁ / I ₂ can be changed _depending on the magnitude of the control signal V _c with respect to the reference signal V _r . That is, it indicates that the gain is changed by the control signal.

The collector current I ₂ thus obtained is obtained as an output signal at the output terminal 3 of the current-voltage conversion unit 300 by the current mirror of the transistors Q ₃ and Q ₄ . now,
The current ratio of the current mirror transistors _{Q 3} and _{Q 4} 1: thought 1, when the value of the resistor _{R 2} and _{R 2,} the output signal _{V 0} becomes _R 2 _{I 2.} At this time, the relationship between the input signal V _i and the output signal V ₀ is represented by FIG. 3 when the control signal V _c is used as a parameter.

Next, the bias operation with the current mirrors of the transistors Q ₁₁ and Q ₅ inserted will be described. This bias action is
To add the collector current of the transistor Q ₅ , that is, the bias current, to the collector current of the transistor Q ₄ . Therefore, the output signal V ₀ now includes the transistor Q
₁₁ and the current ratio of the current mirror of _{Q 5} 1: Taken _{1, V 0 = R 2 (} I 2 + I B) ... (5) is obtained, substituting with reference to further (3) in the equation _{Then, V 0 = R 2 {I} 2 + icc- (V c -V r) / R 1} ... is amended (6). The expression (6) is shown in the graph of FIG. 2, which shows that the output signal V ₀ intersects with all the control signals V _c at one point of V _OA as compared with FIG.

This operation is based on the equation (6), I _{2 is changed} to Ic at V _c = V _r .
When V _c <V _r , the gain V _o / V _i is small, so that a bias amount larger than Icc is added, and when V _c > V _r , the gain is large. We are going to add. This bias amount is linked to I _B , which changes in inverse proportion to the control signal V _c , so that the output signal V ₀ has an intersection with a value larger than R ₂ I ₂ .

Although this intersection has been described when the current ratio of the current mirrors of the transistors Q ₁₁ and Q ₅ is 1: 1, it can be realized with other current ratios, so that the intersection can be obtained at any position.

In addition, although the present embodiment has been shown as an example using the bipolar transistor process having PNP and NPN, CMOS and
It can also be realized by using a device process such as BiCMOS.

According to the present embodiment, by adding the current linked to the operating current inversely proportional to the control signal of the non-linear correction unit to the output current proportional to the control signal of the differential amplification unit, the input obtained by all the control signals can be obtained. The slope of the output signal with respect to the signal,
That is, the gains can intersect at one point.

FIG. 5 shows a configuration example of a video signal amplification system for a color CRT monitor. In FIG. 5, the part to which the present invention is applied is 43.
It is a gain adjustment circuit of 0. In FIG. 5, the same parts as those in FIG. 1 are designated by the same reference numerals. 1 is an input terminal, 3 is an output terminal, 2
Is a control terminal. In addition to applying the variable voltage source 431 shown in FIG. 5 to the control terminal 2, a divided voltage by a volume can be applied.

〔The invention's effect〕

According to the present invention, the slope of the output signal with respect to the input signal obtained by the magnitude of the control signal, that is, the gain can intersect at one point at all gains, so that the video signal amplification for a color CRT monitor or a color television receiver is amplified. The reference value of the system video signal, that is, the black level can be stably obtained without offset.

Further, since the reference value can be set without offset by the gain control circuit itself, there is an effect that it can be used as a direct connection gain control circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is an input / output characteristic diagram of FIG. 1, and FIG. 3 is a transistor Q _{11 of} FIG.
Input-output characteristic diagram when excluding Q ₅ and, Figure 4 is a video signal waveform diagram, FIG. 5 is a block diagram of a video signal amplification system according to the present invention. 1 ... input terminal, 2 ... control terminal, 3 ... output terminal, 4 ... power supply voltage terminal, 100 ... differential amplifier, 200 ... non-linear correction unit, 300 ... electric - voltage conversion _unit, Q 1 to Q ₁₁ ... transistor, _{R 1, R 2, R E} ... resistance, CC1, CC2 ... constant current source, V r _... reference voltage source, V B _... bias power supply.

Claims (2)

[Claims] 1. A variable transconductance type multiplying circuit, wherein one output of a differential amplifying section is taken out in a current form, and a non-linear correcting section for correcting the non-linear operation of the differential amplifying section input transistor to this output current. A gain control circuit characterized by adding a current linked to an operating current. 2. A gain control circuit according to claim 1, which is applied to a color CRT monitor and a video signal amplifying system of a color television receiver.