JPS627210A - Gain control amplifier circuit - Google Patents

Abstract

PURPOSE:To control independently two control terminals individually by using a DC bias current comprising a current from the 1st current source circuit and a current shared by a branching means so as to decide the gain of a signal amplification means. CONSTITUTION:Differential transistor (TR) pair Q5, Q6 constitute the branching means. In setting the entire DC bias current IE of, e.g., a differential amplifier 2, the two control terminals VC1, VC2 adjust the 1st control circuit C1. When the set value is changed in a predetermined range, the voltage of the 2nd control circuit C2 is changed. The range of change is set to (n+1) times or it by selecting optionally the emitter area of a TR Q4 to n-time of that of a TR Q3. In using the circuit for a white balance circuit of a video camera, the terminal VC1 is used for a control terminal for accurate basic adjustment and the terminal VC2 is used for a control terminal of the white balance automatic control circuit.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a gain control amplifier circuit. Regarding circuits.

[Prior art]

BACKGROUND ART In various fields, there are cases in which it is desired to adjust the gain of an amplifier to a reference value during initial setting, and then automatically control and change this value in accordance with the conditions of use.

For example, in the case of a white non-lanance circuit for a video camera, when the product is shipped from the factory, adjustments are made so that the colors of the object illuminated at a predetermined color temperature are accurately reproduced.

However, this adjustment needs to be readjusted when photographing a subject illuminated with light of a different color temperature. For this reason, the white balance circuit itself is connected to the first control terminal for adjusting the circuit characteristics to the color temperature mentioned above when it is shipped from the warehouse, and the internal one for the video camera automatically by pressing the button, etc., depending on the usage conditions. and a second control terminal for changing the set value in response to a signal calculated and output.

Conventionally, as shown in Figure 2, the conventional configuration method has been a configuration in which two stages of variable gain amplifier circuits (AI, A2) are connected in series, but this has the disadvantage of deteriorating frequency characteristics and increasing the number of elements. There is.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned drawbacks.The present invention provides a gain control amplifier that has two control terminals in one variable gain amplifier circuit and can independently control each terminal. The purpose is to provide circuits.

In particular, the present invention reduces the direct current of the differential amplifier to two independent currents. The present invention provides a gain control amplifier circuit that can be individually controlled by control terminals.

[Structure of the invention]

In order to achieve the above object, the present invention provides first and second current source circuits that are commonly controlled via a first control circuit, and the current of the second current source circuit is divided into two. and a second control circuit that controls the distribution ratio thereof, and a DC bias current formed from the current of the first current source circuit and the current p-divided by the branching means. A gain control amplifier circuit was constructed from the determined signal amplification means.

Furthermore, the circuit comprises a first current mirror circuit in which the current ratio of the first and second current source circuits is set to an arbitrary ratio, and the current value is controlled by the first control circuit while maintaining the current ratio. It is recommended to configure it so that

Furthermore, the current distributed by the branching means is combined with the current of the first current source circuit through a second current mirror circuit whose current ratio is set to an arbitrary ratio, thereby increasing the amplification means. It may also be configured to form the DC bias current supplied to! Wear.

〔Example〕

The present invention will be described in detail below using embodiments shown in the accompanying drawings.

FIG. 1 is a diagram showing an embodiment of the present invention. Reference numeral 2 denotes an amplifier 1 whose gain can be changed depending on the DC bias current IE.

Reference numeral 1 denotes a circuit block for controlling the DC bias current generator E according to the present invention. In this circuit, the emitters are commonly connected, one collector is connected to the positive feed line, the other collector is connected to the supply point (a) of the 6-Iass current II, and each base is connected to the second A branching means is constituted by a differential transistor pair (Q5, Q3) connected to the control circuit C2.

Furthermore, a first current source is constituted by a transistor Q6 whose collector is connected to the supply point (a) of the circuit E.

A second current source is constituted by a transistor q whose collector is connected to the emitter connection point of the transistors Q, . Also Q3. A first control circuit C1 is connected as a reference current supply source for transistors i and Q7'l, which together with Q4 constitute a current mirror circuit.

Further, the transistor q has an emitter area n times larger than that of the transistor Q3 so that a collector current n times larger than that of the transistor Q3 flows. Further, the transistor q may be a multi-emitter transistor in which n emitters are connected.

In such a circuit configuration, the collector current of Q6 is
e, the current IE supplied to the amplifier (2) is IE
= Ie + knIe --(1)
There is one. However, k is the current distribution ratio by Q5-Q6FC, and 0≦ and ≦1 f.

An example of a circuit applied to the amplifier (2) having this circuit configuration is shown in FIG. The voltage gain of this circuit is RcI.

G"REIE......(2).

Here, in the case of Figure 1, substituting (1) into (2) and ~
RcI.

[Existence] ~ stone; shore] di ...... (3) Here 1
■ Since the value changes between 0 and 1 depending on c2, the gain can be Rc I o Rc I .

7 to 7 stone T-boxes Changes in width (4).

Since the circuit with this configuration has only one gain stage of the conventional configuration for the signal, its amplitude and one-phase frequency characteristics are good.

In this case, the two control terminals (Vcl, Vc2) can be used to set the entire DC bias IE of the differential amplifier by adjusting the voltage of the first control circuit C1. In order to change f within the specified range, it is sufficient to change the voltage of the second control circuit C2. Also, from equation (2), this change width is arbitrarily selected to make the emitter area of the transistor Q4 n times q. Especially υ its range (
n+1) times.

Therefore, when using this circuit in the white balance circuit of a video camera, %Vcl should be used as a control terminal during delivery or accurate basic adjustment, and %Vc2 should be used as a white balance circuit.
Is it suitable for use as a control terminal for an automatic balance control circuit?
6ru.

FIG. 4 is a diagram showing another embodiment of the present invention.

In the configuration of FIG. 4, the collector current Ie of - controlled via the control circuit C1 is
5. (1-
R)=R ratio 1 is distributed, and the branched current RIe is 1
:Current mirror circuit set to the ratio of n (Q6.Q9
) ft to nRIe, and then combined with the collector current Ie of Q3 to create the DC bias current Ig of the signal amplifying section 2.
It is configured so that

That is, the difference from the embodiment shown in FIG. 1 is that the reference current Ie set from the control voltage VcIK is (1-R):R
The point is that the amount is multiplied by n after being distributed to . Therefore, the current consumption can be reduced compared to the embodiment of FIG. 1 in which Ie is multiplied by n and then distributed to (1-R):R. Furthermore, the bias current supply point (a) to the amplifier (2) is Qs, Q,
It is suitable for low voltage operation because the saturation voltage muff can be lowered by 100 ms. Since equation (1) also holds true in this circuit, when applied to the circuit of FIG. 3, the gain and its variable width are expressed by equations (3) and (4), as in the embodiment of FIG.

FIG. 5 is an example of a circuit implemented by applying the gain control amplifier circuit shown in FIG. 4 to the circuit shown in FIG.
2. Ql5).

Ql2. The Ys of Q13 are each connected to the bias power supply VB3 via a resistor. Q1! The pace is connected via another resistor to the midpoint terminal of a voltage source Vc1, for example, a semi-fixed voltage source for basic White-Nolanance setting, dIJneem. Therefore, by adjusting this semi-fixed volume,! 1llQ12- Q1? By varying the current distribution ratio to the differential transistor consisting of i! l) Ql2 t-Change the flowing DC bias current.

The DC bias currents Ie flowing through Q3 and Q4 are controlled equally through the current mirror circuit.

On the other hand, the second control circuit C2 has Q5. A fixed bias voltage source VB1 is connected to Q6 through a resistor, and an external control terminal is connected to Q6 through a resistor. It is connected to the control output terminal Vc2 of. Therefore, Q5.
Change the current distribution ratio of Q6. The width of this change is determined by setting the current mirror ratio of Qa and Q9 within the range required during circuit design.

A differential amplifier (Ql.

The video signal Vin input to Q2) is amplified by the differential amplifier (Q14.Ql5) constituting the output stage.
Output to out.

〔Effect of the invention〕

In the variable gain amplifier circuit according to the present invention, as described above, two
It has two control terminals, each control terminal can be controlled independently, and it has good frequency characteristics because it has only one gain stage for an input signal. Therefore, it is suitable for a control circuit in which one control terminal is used for basic adjustment and the other control terminal is used for automatic adjustment or fine adjustment.

Furthermore, the width of change in the current controlled by one control terminal,
That is, the gain change width can be set by the current ratio of the current mirror circuit independently of other control terminals. That is, since the cost can be determined by the emitter area ratio of the transistors constituting the current mirror circuit, it is suitable for designing the circuit, especially when implementing it into an IC.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the present invention, FIG. 2 shows a conventional gain control amplifier circuit, FIG. 6 shows an example of an amplifier circuit to which the present invention can be applied, and FIG. The figure shows another embodiment of the present invention. Figure 5 is a circuit diagram when the circuit of Figure 4 is actually applied. (Symbols in the figure) Q, ~Q15...・Transistor, (2 others) Figure 1 Figure 2 Figure 3 Figure 14tm Procedural Amendment February 7z, 1985

Claims (1)

[Claims] 1) First and second current source circuits that are commonly controlled via a first control circuit, and the current of the second current source circuit are
The gain is determined by a branching means for distributing the current to the first current source circuit, a second control circuit for controlling the distribution ratio thereof, and a DC bias current formed from the current of the first current source circuit and the current distributed by the branching means. 1. A gain control amplifier circuit comprising signal amplification means. 2) A first current mirror circuit is configured in which the current ratio of the first and second current source circuits is set to an arbitrary ratio, and the current value is controlled by the first control circuit while maintaining the current ratio. A circuit according to claim 1, characterized in that the circuit is controlled. 3) The signal amplification means combines the current distributed by the branching means with the current of the first current source circuit through a second current mirror circuit whose current ratio is set to an arbitrary ratio. A circuit according to claim 1, characterized in that the circuit forms the DC bias current supplied to the circuit.