JP3018486B2 - Bias circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a bias circuit capable of applying an arbitrary bias voltage and outputting the same current as a current flowing into and out of a bias point.

[Conventional technology]

In a conventional bias circuit for driving the base of a transistor, for example, a common-base bias circuit, when only a low hFE of the driven transistor can be used, the emitter current and the collector current of the transistor are different.

[Problems to be solved by the invention]

As described above, the hFE is low in the grounded base circuit, for example, hFE
If the transistor must be used, for example, when the current is less than 100, the output current becomes smaller than the input current, the loss current becomes 1% or more, and the decrease in gain cannot be ignored. Further, when such a circuit is formed into a monolithic IC, it is difficult to obtain uniform characteristics because the hFE varies considerably for each manufacturing lot.

[Means for solving the problem]

The bias circuit according to the present invention includes first and second transistors of the same conduction type, and connects the base and collector of the first and second transistors and one end of the second current source in common. , The other end of the second current source and one end of the first current source are commonly connected, further connected to a first power supply terminal, and the other end of the first current source is connected to the collector of the first transistor. The base of the third and fourth transistors, which are different from the first and second transistors in conduction type, are connected in common to serve as bias current input terminals, and serve as bias voltage input terminals.
The collector of the fourth transistor is commonly connected and connected to the second power supply terminal, the emitters of the second and fourth transistors are commonly connected, and the emitters of the first and third transistors are commonly connected. As a bias voltage output terminal.

〔Example〕

Next, the present invention will be described with reference to the drawings. FIG. 1 shows a basic circuit of the present invention. In FIG. 1, the current source I1
I2 has the same current value. The transistors Q1, Q2, Q3, and Q4 form a current mirror circuit that uses the base voltage of the transistors Q3 and Q4 as a reference potential and uses the collector of the transistor Q2 as an input point and the collector of the transistor Q1 as an output point. The terminal T4 to which the transistors Q3 and Q4 are connected in common
Is a bias voltage input terminal. Power supply terminals T3 and T5 are set to high potential and low potential with respect to terminal T4, respectively.
Set the voltage to operate Q1, Q2, Q3, Q4. The terminal T1 serves as a bias voltage output terminal, and the terminal T2 serves as a correction current output terminal. The bias voltage output terminal T1 is an output of an emitter follower using the transistor Q3 having the bias voltage input terminal T4 as an input. As for the transistors Q1, Q2, E3, and Q4 constituting the current mirror, if the area ratio is 1: 1 for the transistors Q1 and Q2, and Q3 and Q4, the collector currents of the transistors Q1 and Q2 are equal, and as described above. As described above, if the current sources I1 and I2 have the same amount of current and there is no current inflow and outflow at the bias voltage output terminal T1, no current flows in and out of the correction current output terminal T2. When a current flows into the present bias circuit from the bias voltage output terminal T1, the flowing current becomes an increase in the emitter current of the transistor Q3, and the base-emitter voltage VBE of the transistor Q3 increases by the flowing current. On the other hand, VBE of transistor Q1
Reversely decreases by the VBE increase of the transistor Q3, the collector current of the transistor Q1 decreases by the inflow from the bias voltage output terminal TQ, and the inflow current from the bias voltage output circuit T1 The same amount of current flows out. Conversely, when a current flows out of the bias voltage output terminal T1, the same amount of current as the outflow current similarly flows in from the correction current output terminal T2. The potential of the correction current output terminal T2 is determined by the potential of the circuit to which T2 is connected.

Next, FIG. 2 shows a circuit actually using the bias circuit of the present invention. In FIG. 2, elements having the same functions as those in FIG. 1 are denoted by the same reference numerals. FIG. 2 is a circuit for inverting the signal current, which is obtained by inverting the current of the input current signal source IS at the signal output terminal T6. Terminals T3 and T4 are power supply terminals, and transistors Q5, Q6, Q7 and Q8 constitute a current mirror. The emitter areas of Q5 and Q6 are the same, and the collector current I1 of the transistor Q5 and the collector current I2 of the transistor Q6 have the same current value. Transistor Q8
Is selected to be larger than the DC bias current of the current signal source IS, a current I4-IS flows through the emitter of the transistor Q9. The transistor Q9 is a grounded base circuit. However, when the hFE of the transistor Q9 is low, the collector current of the transistor Q9 is reduced by the base current IB of the transistor Q9, and the signal current is lost.However, from the correction current output terminal T4 of the bias circuit,
Correction current of the same amount as the base current IB of transistor Q9
Since the IF flows out and is added to the collector current of the transistor Q9, the loss in the common base circuit of the transistor Q9 is eliminated. The diode D1 is for securing the potential of the correction current output terminal 2 to a potential for normal operation of the transistor Q1. The transistors Q10 and Q11 are current mirror circuits, and a signal current inverted from the input signal source IS can be obtained from the signal current output terminal T6.

〔The invention's effect〕

As described above, according to the bias circuit of the present invention, the same amount of current as flowing into or out of the bias point can be flowed out or flowed in. Therefore, even when the hFE of the bias driving transistor is low (for example, hFE Is 10
0 or less), the loss is negligible even if the signal current passes through the bias-driven transistor (1 / (1 + hF)
E)), there is almost no gain reduction, and stable operation with little gain variation with respect to IC manufacturing variation (hFE variation) can be obtained.

[Brief description of the drawings]

FIG. 1 shows a basic operation circuit of the present invention, and FIG. 2 shows a use example of the present invention. Q1-Q11: Transistor, D1: Diode, I1-I3
... DC current source, IS ... Signal current source.

Claims (1)

(57) [Claims] A first transistor having a same conductivity type, a base of the first transistor, a base and a collector of the second transistor, and one end of a second current source connected in common; The other end of the second current source and one end of the first current source are connected in common, further connected to a first power supply terminal, and the other end of the first current source is connected to the collector of the first transistor. A correction current output terminal, the bases of third and fourth transistors different from the first and second transistors in conduction type are connected in common to serve as a bias voltage input terminal, and the third and fourth transistors The collector is connected in common to the second power supply terminal, the emitters of the second and fourth transistors are connected in common, the emitters of the first and third transistors are connected in common, and the bias voltage output terminal Bias circuit.