JPH053926B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a transistor amplifier, and particularly relates to an improvement of a base current correction circuit for correcting the base current of an amplifying transistor.

(Prior Art) As is well known, in transistor amplifiers, a base current correction circuit is used to prevent error components such as offsets from occurring in the output signal due to the base current flowing through the amplifying transistor. is provided.

FIG. 5 shows a conventional base current correction circuit used in a transistor differential amplifier. That is, in the figure, 11 and 12 are input terminals, which are connected to the bases of NPN type transistors Q1 and Q2, respectively. These transistors Q1,
Each collector of Q2 is connected to a power supply terminal 13 to which a positive voltage Vcc is applied via resistors R1 and R2, respectively. And the above transistor Q
1 and Q2 have their respective emitters commonly connected to each other, and the connection point is connected to the power supply terminal 15 to which the negative voltage Vee is applied via the constant current source 14 of the output current 20, so that a differential Amplification circuit 16
It consists of

Here, between the two power supply terminals 13 and 15,
An NPN type transistor Q3 and a constant current source 1 that generates an output current 0 which is 1/2 of the constant current source 14 for constant current biasing the transistor Q3.
7 are connected in series. Then, the base current of this transistor Q3 is reflected by a current mirror circuit 18 consisting of PNP type transistors Q4 to Q6, and is reflected by the transistors Q1 and Q6.
2, the base currents of the amplification transistors Q1 and Q2 are corrected.

Here, the input bias current 1 of the circuit shown in FIG.
Let the current amplification factors of the transistors of the shape βn and
When βp is assumed, 1=3/(βp+3)・0/(βn+1). That is, since the input bias current 1 without base current correction is 0/(βn+1), by performing base current correction, an improvement of 3/(βp+3) is achieved.

Furthermore, FIG. 6 shows another conventional base current correction circuit, in which the transistor Q shown in FIG.
The diode connection of No. 4 (that is, the collector-base common connection of transistor Q4) is replaced with a PNP type transistor Q7. The input bias current 1 in this case is 1=3/{βp(βp+1)+3}・0/(βn
+1), which is an improvement of 3/{βp(βp+1)+3} times compared to the case without base current correction.

However, in the conventional base current correction circuit shown in FIGS. 5 and 6, the base current of the transistors constituting the current mirror circuit 18, that is, the current supplied to the bases of transistors Q4 to Q6, is Since the correction current is obtained from the base terminal, errors tend to occur in the correction currents supplied to the bases of the amplification transistors Q1 and Q2, and there is a problem that accurate base current correction cannot be obtained. There is.

(Problems to be Solved by the Invention) As described above, in the conventional base current correction circuit, errors tend to occur in the correction current supplied to the base of the amplification transistor, and accurate base current correction cannot be obtained. There is a problem.

Therefore, this invention was made in consideration of the above circumstances, and reduces the error in the correction current supplied to the base of the amplification transistor with a simple configuration.
Furthermore, it is an object of the present invention to provide an extremely good base current correction circuit for a transistor amplifier that can obtain accurate base current correction.

[Structure of the Invention] (Means for Solving the Problems) That is, the base current correction circuit for a transistor amplifier according to the present invention corrects the base current of a transistor constituting a current mirror circuit by using a constant current biased transistor, The constant current bias is obtained from the connection portion of this transistor with a constant current source for constant current bias.

(Function) According to the above configuration, it is possible to reduce the error in the correction current supplied to the base of the amplification transistor, and in turn, it is possible to obtain accurate base current correction. It is.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. In FIG. 1, the same parts as in FIG. 5 are shown with the same symbols, and only the different parts will be explained here. That is, the base common connection point of each of the transistors Q4 to Q6 constituting the current mirror circuit 18 is connected to the connection point between the emitter of the transistor Q3 and the constant current source 17 via the diode D1 with the polarity shown. What we did is different from the conventional method.

According to such a configuration, the input bias current 1 is as follows: 1=3/{βp(βn+1)+3}・0/(βn
+1), which is an improvement of 3/{βp(βn+1)+3} times compared to the case without base current correction. Now, if we compare the formula for the input bias current shown in this example with the formula for the input bias current shown in Figure 5 earlier, this example has an improvement of approximately 1/(βn+1) times. The error component included in the correction current supplied to the bases of transistors Q1 and Q2 is reduced. For this reason,
As a result, accurate base current correction can be obtained. In addition, diode D
Reference numeral 1 functions to prevent saturation of the transistor Q4.

FIG. 2 shows another embodiment of the invention, in which the diode D1 shown in FIG. 1 is replaced with a PNP type transistor Q8. The input bias current 1 in this case is 1=3/{βp(βp+1)(βn+1)+3}・
0/(βn+1), which is an improvement of 3/{βp(βp+1)(βn+1)+3} times compared to the case without base current correction.Similarly to the above, this value is Compared to the conventional one shown in Fig. 6, this is improved by approximately 1/(βn+1) times.

FIG. 3 and FIG. 4 each show a modification of each of the above embodiments. First, Figure 3 shows the first
A modification corresponding to the embodiment shown in the figure is shown. That is, the current mirror circuit 18 is
It has a configuration consisting of PNP type transistors Q9 to Q16, and the common connection point of the bases of transistors Q13 to Q16 is connected to the connection point between the emitter of transistor Q3 and constant current source 17 via diode D1. be.

According to such a configuration, the transistor Q13
Since Q16 acts to equalize the collector potentials of transistors Q9 to Q12, it is possible to prevent collector current errors of transistors Q9 to Q12 from occurring due to the Early effect. In this case, the input bias current 1 is 1=4/[{βp ² (βn+1)/(βp+1)}+
4]·0/(βn+1), and the input bias current 1 is improved by a factor of 4/[{βp ² (βn+1)/(βp+1)}+4].

Moreover, FIG. 4 shows a modification corresponding to the embodiment shown in FIG. 2. That is, the current mirror circuit 18 is replaced by a PNP type transistor Q.
17 to Q24, and the transistor Q
The base common connection point of transistors 21 to Q24 is connected to the emitter of transistor Q8.

Even with such a configuration, the transistor Q2
Since transistors Q1 to Q24 act to equalize the collector potentials of transistors Q17 to Q20, it is possible to prevent collector current errors of transistors Q17 to Q20 from occurring due to the Early effect. In this case, the input bias current 1 is 1=4/{βp ² (βn+1)+4}・0/
(βn+1), and the input bias current 1 is improved by a factor of 4/{βp ² (βn+1)+4}.

Here, if we compare the input bias current equations shown in FIGS. 3 and 4 above with the input bias current equations shown in FIGS. 5 and 6 above, we can see that FIGS. The improvement is approximately 4/3 (βn+1) times, and the error component contained in the correction current supplied to the bases of transistors Q1 and Q2 is reduced.

It should be noted that the present invention is not limited to the above-described embodiments, and can be implemented with various modifications without departing from the gist thereof.

[Effects of the Invention] Therefore, as detailed above, according to the present invention, it is possible to reduce the error in the correction current supplied to the base of the amplification transistor with a simple configuration, and furthermore, to perform accurate base current correction. It is possible to provide an extremely good base current correction circuit for a transistor amplifier that can be obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing one embodiment of a base current correction circuit for a transistor amplifier according to the present invention, FIG. 2 is a circuit configuration diagram showing another embodiment of the invention, and FIGS. 3 and 4 are A circuit configuration diagram showing a modification of the embodiment shown in FIGS. 1 and 2, respectively, and FIGS. 5 and 6 are circuit configuration diagrams showing a conventional base current correction circuit, respectively. 11, 12...Input terminal, 13...Power terminal,
14... constant current source, 15... power supply terminal, 16...
Differential amplifier circuit, 17... constant current source, 18... current mirror circuit.

Claims (1)

[Claims] 1: a first transistor for amplification; a second transistor, one end of which is connected to a first power supply and whose polarity is the same as that of the first transistor; a constant current source connected between the other end of the current path and a second power source and biasing the second transistor with a constant current; and a constant current source that returns the base current of the second transistor to the base of the first transistor. a current mirror circuit connected between the commonly connected bases of the transistors constituting the current mirror circuit and the other end of the current path of the second transistor, and supplying base current to the transistor constituting the current mirror circuit; A base current correction circuit for a transistor amplifier, comprising circuit means for supplying the base current. 2. The circuit means has one end of the current path connected to the commonly connected bases of the transistors forming the current mirror circuit, and the other end of the current path connected to the other end of the current path of the second transistor. 2. A base current correction circuit for a transistor amplifier according to claim 1, comprising a diode. 3 The circuit means has one end of the current path connected to the commonly connected bases of the transistors forming the current mirror circuit, the other end of the current path connected to the second power source, and the base connected to the second power source. 2. A base current correction circuit for a transistor amplifier according to claim 1, comprising a transistor connected to the other end of a current path of the transistor.