JPS62254507A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To decrease the variation of an output DC potential by inserting a resistor in series with a base of a specific transistor (TR). CONSTITUTION:A resistor R11 is inserted in series with a base of a TR Q8. The inserted resistor R11 produces a potential difference between a bias potential VB2 and the base of the TR Q8 when a common base current amplification factor of an NPN TR is small. The potential difference acts like decreasing collector currents of TRs Q8, Q9, Q10 thereby finally decreasing the output DC potential V2, then the variation of the voltage V2 is corrected. Since the variation of the DC potential at the output terminal due to the variation of the common base current amplification factor of the NPN TR is decreased, the variation in the dynamic range of the output signal of the amplifier circuit is decreased. Even when the circuit of the next stage is coupled in terms of DC, the variation in the operating point is decreased.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a transistor differential amplifier circuit including a constant current source, and more particularly to a circuit that reduces variations in output DC potential due to variations in the current amplification factor of NPN transistors. .

[Conventional technology]

Conventionally, as an amplifier circuit in an integrated circuit, Japanese Patent Application Laid-Open No. 59-1
The method described in No. 25107 has often been used.

FIG. 2 shows a practical circuit in which the conventional constant current source is replaced with a current mirror circuit, where 3 is a power supply voltage supply terminal, and 4 to 6 are bias voltage sources 7 are gain control voltage sources.

The input signal voltage is applied to terminals 1, 1', and a first circuit consisting of transistor Q, resistor R, and bias voltage VB2
constant current source and transistor (1-Qt and resistor R1,
The current is converted into a signal current by the action of the differential circuit consisting of R, and passes through the transistor Q to become the collector current of the transistor Qs. Next, transistors Q, ~Q,. and the collector current of transistor Qro, which is the output of the second constant current source consisting of resistors R6 to R3°, and transistor Q.

The difference current between the collector current of Q? and the collector current of Q? reaches the collector. Here again, transistor Q and resistor R1
The transistor Qy which is the output of the third constant current source consisting of
The difference between the collector current and the difference current passes through the common-base transistor Q6, and is finally converted into an output voltage by the resistor R6, which is taken out from the terminal 2.

This circuit is an NPN transistor Qs -Qt -Qs
Although Q6 and Q6 are connected in cascade, the DC potential of output terminal 2 can be set low, making it an especially effective amplifier circuit when you want to widen the dynamic range of the output signal with a low-voltage integrated circuit. It is.

[Problem that the invention seeks to solve]

However, the above-mentioned conventional technology has a problem in that the DC potential (hereinafter referred to as r) of the output terminal 2 varies greatly. V when there is no signal in FIG. 2 can be calculated as follows. In the following two, transistor Q, (B m
1 to 1o) collector and emitter.

The base currents are represented by ICn, I, , I, and n, respectively, and the directions of the currents are NPN transistors Q1 to Q&
(DIcn.

IBn and PNP transistors Q, ~Q,. I,
For r&, the direction flowing into the transistor is positive, and for the others, the direction flowing out from the transistor is positive. It is assumed that the base-emitter voltage and common base current amplification factor of the pup transistor are all equal, and each i'xz
It is expressed as p and α. Similarly, let the base-emitter voltage and base-ground current amplification factor of the NPN transistor be V□ and α, respectively. Further, it is assumed that the gain control voltage VC is negative and sufficiently large, and the transistor Q4 is in a cut-off state. At this time, IC9” 189 +1810” Ice °°−
−−−−:−−−−−−−−−−−−(1) IC9−
αP I...
...open...song...hit...(211C8-α1111
・・・・・・・・・・・・－・・・・・・・・・・・・
・Song・・Open−・・Song・T311B, = (1-αP)
Hit 9 IK songs... 1 ~ Songs... (4) IJ.

=(1-αp>1g, . . .
・Song...(5) II! ! 10R10=II! 9R9
°°°°°゛°“°“°°10°°°°0°°1a°1
0°°°0°0(6) IC7°=αP/7110 ・
・・・－・・・・・・・・・・・・・・・・・・・・・
・・・・・・・From equation (7) 111 to (7), ICI
When looking for the relationship between Q and zga, when RI-R1 and there is no signal (input terminals 1 and 1' are at the same potential), then.

Next, calculating the collector current IC6 of the transistor Q6, IC6-aIE&=α(Ic," Ics -1c+a
) -== al) IC7-α117 relationship and (8
) formula and α [by substituting the formula, we get V! -Vccx, 'C&・・・・・・・・・−・
...beat...beat...music...beat...Ia3~(
From formula 14, %Vl is as follows.

・・・・・・・・・(19 a! As can be seen from equation 9, V depends on the transistor base ground current amplification factor α2 and α. For example, consider the case of the following constant .

The relationship between α and V at this time is a! It is calculated from Equation 9 and graphed as shown in Figure 3.

As is clear from FIG. 3, when the common base current amplification factor α of the NPN transistor becomes smaller, the circuit of FIG.
Since the DC potential V at the output terminal 2 increases, there are problems in that the dynamic range of the output signal decreases, and when the next stage is DC coupled, the operating point changes.

The object of the present invention is to eliminate the drawbacks of the above-mentioned prior art.

An object of the present invention is to provide a transistor amplifier circuit with small variations in output DC potential.

[Means for solving problems]

The above object is achieved by inserting a resistor K in series with the base of the transistor Q in FIG.

[Effect]

The insertion resistor generates a potential difference between the bias potential VB□ and the base of the transistor Q8 when the common base current amplification factor of the NPN transistor is small.

This potential difference is the transistor Qa=Qe, Q+. works to reduce the collector current of V, and eventually the output DC potential V
, it is possible to correct variations in %V.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

Figure 1 shows a resistor R11 in series with the base of the transistor Q.
The only difference from Figure 2 is that .

In Figure 1, VB2 188 R11VBII = IMB RB
°゛°°°゛°°°°°°°゛°°゛°°°゛°”°
aSIE8=C'-α) IMB ・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
Since αD holds true, and the other equations are exactly the same as in the case of FIG. 2, the output DC potential V when there is no signal is as follows.

V, = Vcc-R6(VB2-VB, )α!・・・
・・・・・・・・・・・・・a9 As a calculation example, graph the relationship between the common base current amplification factor α of the NPN transistor and the output DC voltage V2 using the same constant as in Figure 3 and the insertion resistor R11 as a parameter. The result will be as shown in Figure 4.

As is clear from FIG. 4, by appropriately selecting the value of the insertion resistor R11, V2 can be kept at a substantially constant value over a wide range of α. A simple way to choose the value of resistor R11 is to use the value of V when α is the minimum value and α-1
It is sufficient to set a value such that the values of r when ,
In the case of Fig. 4, Ω is considered to be the optimal value for R11=9, but α and V! Since the relationship between .alpha. and .alpha. is not linear, when .alpha. is an intermediate value between the above minimum value and 1, r is a little low.

FIG. 5 is a circuit diagram showing another embodiment of the present invention, and P
The resistor R11 is designed to compensate for a change in the base terminal of the transistor Q+o due to a decrease in the current amplification factor of the NP transistor. Also, the transistor Qst
+Qst lowers the impedance of the base terminal of the transistor Q1°. In this case as well, the resistance R
II functions in the same manner as in FIG. 1, and can keep the output DC potential V substantially constant.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to reduce the variation in the DC potential of the output terminal due to the variation in the common base current amplification factor of the NPN transistor, and therefore the variation in the dynamic range of the output signal of the amplifier circuit is reduced. Further, even when the next stage circuit is coupled in a direct current manner, the variation in the operating point is reduced.

[Brief explanation of drawings]

1 and 5 are circuit diagrams showing an embodiment of the present invention. FIG. 2 is a circuit diagram of a conventional technology. FIG. 4 is a graph showing the relationship between the output DC potential and the common base current amplification factor of the NPN transistor in the circuit of FIG. 1.1'・・・・・・・・・・・・Input terminal 2・
・−・・・・・・・・・・・・・・・・・・Output terminal 3・
・・・・・・・・・・・・・・・・・・・Power supply voltage supply terminals 4 to 6・・・・・・・・・Bias voltage source 7
・・−・−・・・・・・・・・・・・・・Gain control voltage source 8 ・・・・・・・・・・・・・・・・・・・・・・・DC level shift circuit QI-QIt ...Transistors R0 to R3! ...Resistance Figure 1 Figure 2 Figure 4 (V)

Claims (1)

[Claims] a circuit that includes a first constant current source and converts an input voltage into a first output current; and a circuit that takes the difference between the second constant current source and the first output current and outputs a second output current. , a DC level shift circuit, a circuit that calculates the difference between a third constant current source and the second output current, and outputs a third output current;
The first and third constant current sources include first and third NPN transistors, respectively, and the emitters of the first and third transistors are connected to the first and third NPN transistors, respectively. , is connected to ground via a third resistor, the base is connected to a common reference potential, and forms part of a first current mirror circuit that supplies a constant current from the collector, and the second constant The current source includes a second NPN transistor that is part of the first current mirror circuit, and first and second PNP transistors that form the second current mirror circuit.
A collector of the second NPN transistor, which is one of the outputs of the first current mirror circuit, and a collector of the first PNP transistor, which is an input of the second current mirror circuit, are connected to each other. An amplifier circuit characterized in that the base of the second NPN transistor is connected to the reference potential via a fourth resistor.