JPH01200811A - Automatic gain control circuit - Google Patents

Abstract

PURPOSE:To clearly remove the noise of an input signal by adding a resistance to the emitter of a second transistor(TR) in an AGC circuit to have a current mirror circuit. CONSTITUTION:The input signal from an input terminal VIN is inputted through an amplitude/voltage converting circuit A/V to the base of a TR Q1. A current i1 to be approximately equal to a collector current to flow according to the base current of the TR Q1 is made to flow to the collector of a TR Q2. At the same time, a collector current i2 of a TR Q3 of a current mirror circuit 1 is also made to flow according to the base voltage of the TR Q1. At such a time, since the collector voltage of the TR Q2 is lowered by a resistance RE, the current i2 is made into a value larger than the current i1. By inputting the current i2 to the bases of TRs Q4 and Q5, even with the input signal VIN to be small, the current i2 of the current mirror circuit 1 is made into the large current, and it is inputted to a non-inverting amplifier circuit A. Consequently, since a gain is made large, simultaneously, quick and constant, the noise of the input signal can be clearly removed.

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention relates to automatic gain dividing circuit (hereinafter referred to as AGC circuit) K.
In particular, it relates to improving its gain characteristics.

[Conventional technology]

Is Figure 3 a conventional general current mirror circuit? AG with
It is a C circuit. In the figure, (OP) is the -1000 input terminal (VIN), the operand to which the VC input signal is applied, (
A/V) is the amplitude voltage conversion 101 voltage that converts the amplitude 11111 of the input signal (VrN) into a voltage, and (R1) is the voltage converted by the amplitude voltage conversion +1=ll path (A/V) applied to the base. npn) transistor, (R2)
μpnp) transistor connected to the collector of npn) transistor (R1), (R3) forming a current mirror circuit with pnp transistor (R2) pnp) transistor, (R4) based on the collector current of transistor (R3) npn transistor, (R
5) is its base IC p n p ) transistor (R3
) is applied, and the npn) transistor is reversely connected to the npn) transistor 1o4).
R1) is a resistor, and npn transistor (θ4), (
The common output of the operational amplifier (OP l(/J
It is input to the power terminal through this resistor (R1). (
R21, (Rs) is a resistance, and this
P) is a resistance (+(11, (R2)) is the resistance (R1],
npn) transistors (θ4) and (θ5) constitute a non-inverting term width circuit IAl. (Vout) is the output terminal of the operational amplifier N)P)t/>, and (tmaaa) is the power supply terminal applied to the current mirror circuit (21).

Next, the operation will be explained. At the same time, the input signal is applied to the -1000 input terminal of the operational amplifier 5 (OP), and the input signal is input from the input terminal (7I N ) and is converted to the input signal through the open circuit (A/V). The loss width is converted into a voltage and input to the base of the transistor (θ1).

A collector current of the transistor (θ1) flows in accordance with the base, and a current approximately equal to this collector current flows to the collector of the transistor (θ2). Transistor (θ2
) and (θ3) constitute a current mirror circuit (21), so the collector current of transistor Cθ3 is the same as the collector current of transistor (θ2).
2) flows depending on the base voltage. Then, the collector current of the transistor (θ3) is the transistor C4)(θ
5) is input to the common base of the transistor (θ4) (
A common output current of θ5) flows. This output current increases as the base current of the transistor (θ+1('75) becomes thicker, and becomes constant at a certain value.Then, the output of the transistor (θ4) (θ5) is passed through the resistor (R1) i to the above-mentioned It is input to the other terminal of the operational amplifier (oP).This operational amplifier (OP) is also connected to the resistor IRQ1 (R3) (
R1), transistor (θ4) C84) creates a non-inverting amplifier circuit? Purchase LTL power terminal (vout) 7/:
It is output from

At that time, input signal voltage (VIN) - output signal low voltage (V
Out) characteristics are shown in FIG. In this figure, the amplitude voltage conversion lo] path (A/VJ ct) output voltage is (VA
/V). (vrNl) is the transistor (θ4) (
θ5) is the input signal voltage that u3 starts to generate, and (VIN
2) is an input signal voltage at which the output current of the transistors (θ4) (θ5) becomes constant. (vzul)-(Vxu2
), the output currents of the transistors (θ4) and (θ5) are changing. As a result, the operation as described above results in a characteristic curve as shown in FIG. The gain characteristic curve shown in this figure shows that when the input signal voltage is below (vrN), the input signal voltage is clearly removed, and when it is above (VIN2), it is clearly amplified. This means that the width between (vxnx) and (vxpt2) is changed by m depending on the input signal voltage.

[Problem I that the invention seeks to solve]

AGC circuit with conventional general current mirror circuit
11 is configured as described above, the characteristic between (vrsx) and (vnr2) in FIG. 4 remains constant. In other words, there was a problem that noise in the input signal was not clearly removed.

This invention was made in order to eliminate the above-mentioned royalties, and it is an AGC that can clearly remove noise from input signals.
The purpose is to obtain a circuit.

〔assignment? Means to solve]

AGC having a current mirror circuit according to the present invention
The circuit has a resistor of y3 added to the emitter of the second transistor.

[Effect]

In the AGC circuit according to the present invention, the current 2 for increasing the width of the inversion term can be increased by the resistor attached to the emitter of the second transistor, and as a result, the gain characteristics are improved.

[Embodiments of the invention]

Figure 1 Hakono Invention'7) -Real* $I VC becoming AG
It is a C circuit.

In the figure, are the same symbols as in Figure 3 corresponding parts? The explanation will be omitted. Hereinafter, a specific enumeration of this invention will be explained. In the figure (RE l is the current mirror circuit I)
ll 'i Constituting PNP) transistor (θ1)
is a resistor connected to the emitter of .

The following describes the operation of the AGC circuit which is an example of the present invention.An input signal is input from the input terminal (VIN), and the input signal is input through the Iff circuit (A/V). is input to the base of the transistor (θ1), which is converted to a low voltage. A collector current of the transistor (θ1) flows through the base magnetic pressure VC, and a collector current (hereinafter referred to as current 11) of the collector 4 (transistor lθ2, which is substantially the same as the current) flows.

At the same time, current mirror circuit 111 Gold? The collector circulation current (hereinafter referred to as current 1) of the transistor (θ3)
2) also flows based on the pace voltage of the transistor (θ1). At this time, the resistor (RF, ) 7C: Therefore, the transistor (
Since the collector voltage of θ2) decreases, the current 12 becomes a current larger than the current I. The current i2 is input to the base of the transistor (ua l (G l). As a result, even if the input signal is small, the current i2 of the current mirror circuit 12
Since the current becomes a large current and can be input to the non-inverting amplifier circuit/Al, the current becomes constant and quickly becomes constant.

Input signal voltage at that time (VII - output signal voltage (V□)
ua) characteristics are shown in FIG. In the figure, the same symbol as in Fig. 4 is i.
The explanation is omitted since it constitutes a considerable part. (VII
3) is the input signal voltage at which the output currents (θ4) and (θ5) in the above AC three-time crystal are constant and the gain of the AGC circuit is constant. The characteristics of the gain characteristic curve shown in this figure are different from those of the conventional AGCLgJ path when the input signal is (V
II2) The gain becomes constant at a lower value (V+s3). Then, the slope between (VII1) and (Vxs3) becomes large and becomes zero. This shows that input signals below (VIN) can be clearly removed.

〔Effect of the invention〕

As described above, according to the present invention, the emitter VC of all second transistors in the AGC circuit having a current mirror circuit
The advantage of this method is that the noise in the input signal can be clearly removed because the resistor is connected to the arm.

[Brief explanation of the drawing]

Figure 41 is a circuit diagram showing the entire AGC circuit according to the present invention.
The figure is a graph showing the gain characteristic (characteristic of output voltage (vout) versus input signal voltage (VIN)K) curve of the AGC circuit according to the present invention, FIG. 3 is a circuit diagram showing a conventional AGC circuit, and FIG. 3 is a graph showing gain characteristics of a conventional AGCLgJ path. In the figure, (θ1), lθ4) (θ5) are NPN transistors, (θ2), fθ3) are PNP transistors, (REI. fRl), (R21, 1R31 are resistors, (OP company operational amplifier circuit, (tVcc) is a The continuous terminal (Vuq) is an input terminal.

Claims (1)

[Claims] an operational amplifier to which an input signal is applied to one input terminal; a circuit for converting the amplitude of the input signal into a voltage; and a first transistor of one polarity to which the voltage converted by the conversion circuit is applied to the base. A second transistor which is tangential to the collector of the first transistor and has a polarity opposite to that of the first transistor, and a third transistor that forms a current mirror circuit with the second transistor have their collector currents in common. is applied to the base of
The fourth and fifth transistors are connected in reverse to each other, and the common output of the fourth and fifth transistors is applied to the other input terminal of the operational amplifier, and the fourth and fifth transistors are connected to the emitter of the second transistor. Automatic gain control circuit featuring a resistor.