JPS5841683B2 - current amplification circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current amplification circuit suitable for integrated circuits, and in particular to one that obtains an output current that is exactly proportional to an input current.

FIG. 1 shows a conventional current amplification circuit, in which E is a DC bias source, V't is an input voltage source, Ql is a diode, and the base and collector of the transistor are commonly connected to be used as a diode.

Q2 is an amplification transistor.

Note that R1 is a relatively large resistor for converting the input voltage source vi into a current source.

According to this circuit, the collector potential of transistor Q1 is approximately 0.7 V, so transistor Q2
The base potential of is also approximately 0.7V.

In this state, a signal current ■ flows through the resistor R1 to the base of the transistor Q2.

When +11n (■o is a DC bias current and 11'H is an AC signal current) is applied, an output current ratio of approximately 1:1 is applied to the collector of the transistor Q2.

2+i0 flows. Therefore, the amplification degree β of the composite i of the transistor Q2 and the diode Q1 becomes β-02-↓1.

IOtIH However, this amplifier circuit has a drawback that the value of the composite amplification degree β varies widely.

This has a major disadvantage in that external circuits for integrated circuits require correction in the circuit, which increases the number of manufacturing steps and increases the number of defective integrated circuits.

The large variation a in the composite amplification degree β in the conventional circuit is due to the fact that the base-emitter voltage VBE2 versus emitter current characteristic of the amplifying transistor Q2 does not match the base-emitter voltage VBE1 versus emitter current characteristic of the transistor Ql.

That is, the collector-emitter voltage VC of transistor Q1
Although EI is substantially fixed at its base-emitter voltage ■BE1, the collector-emitter voltage VCE2 of transistor Q2 fluctuates depending on the current flowing therethrough, effectively changing the collector potential of each transistor. This is because it was not possible to keep them the same.

In order to eliminate these drawbacks, a circuit as shown in FIG. 2 has been proposed, which will first be described in detail.

In Figure 2, a second transistor Q is connected to the output current path connected to the collector of the first transistor Q2 for amplification.
A rectifying junction element, that is, a diode made of the transistor Q1, is connected between the base and emitter electrodes of the first transistor Q2, and a signal voltage source Vi and a bias source E are connected to the base electrode of the first transistor Q2.
are connected through a resistor R1, the emitter electrode of the second transistor Q3 is connected to the collector electrode, and the first transistor Q is connected to the base electrode of the second transistor Q3.
A bias voltage was supplied such that the collector-emitter voltage VCE2 of the second transistor Q3 was approximately equal to the forward conduction voltage of the rectifying junction element (transistor Q), and the output current was taken out from the collector electrode of the second transistor Q3. It is something.

The bias voltage to be supplied to the base of the second transistor Q3 is supplied from the midpoint of the connection between the series circuit of two diodes Q4 and Q5 and the resistor R3.

With this configuration, the collector-emitter voltage VCE2 of the first transistor Q2 is approximately the threshold value of the diode Q5, vBE=o, 7v, and the collector-emitter voltage VCEI of the transistor Q1 is also approximately v(,
E, = o, 7v, and the first transistor Q2
The base-emitter voltage to emitter current of transistor Q1 corresponds almost completely to 1:1, and in this state, the second
The collector output current of transistor Q3 corresponds to its emitter current in a 1:1 ratio.

Therefore, in this circuit, the collector voltage of the first transistor Q2 is made the same as its base voltage, so the base-emitter voltage VBE vs. emitter current ■E characteristic of the first transistor Q2 matches the VBE vs. ■E characteristic of the transistor Q1. Therefore, variations in the composite amplification degree β can be prevented.

By the way, in the embodiment shown in FIG. 2, the collector-emitter voltage VCE2 of the transistor Q2 is substantially equal to VBE.
Since the input current, that is, the collector current of transistor Q1, and the output current, that is, the collector current of transistor Q
Although the two collector currents are substantially the same, strictly speaking, there is a slight difference.

In other words, since the input current changes according to the signal current,
As a result, the base-emitter voltage VBE1 of the transistor Ql also changes.

This voltage fluctuation is transmitted to the collector-emitter voltage VCEI of the transistor Q1 and the base-emitter voltage VBE2 of the transistor Q2, but the collector-emitter voltage VCE2 of the transistor Q2 is given by a fixed bias power supply formed by diodes Q4 and Q5. Because it is
It is not possible to follow this.

The present invention provides a current amplifier that further improves the above-mentioned drawbacks, and will be described in detail below with reference to FIG. 3.

In FIG. 3, parts corresponding to those in FIG. 2 are designated by the same reference numerals, and detailed explanation thereof will be omitted.

In FIG. 3, a path for supplying input current to a first diode made of transistor Q1 connected between the base and emitter of transistor Q2 of Tate 1 is connected to a second diode made of transistor Q4, and the diode The voltage across Q1 and Q4 is transferred to the second transistor Q.
It is designed to be supplied to the base of No. 3.

By configuring in this way, the diode Q is
It can also be used as diode Q5 shown in the figure, and even if the input current fluctuates and the base-emitter voltage of diode Q1, which is a transistor, changes, the base-emitter voltage of diode Q4, which is a transistor, changes. Since the base-emitter voltage of the transistor Q3 changes similarly, the collector-emitter voltage VCE2 of the transistor Q2 can also follow it.

In this way, the collector potentials of transistors Q and Q2 become substantially equal in their operating states, making it possible to equalize the input current and the output current.

Here, the transistor Q6 forms an emitter follower for the input voltage source Vt, and together with a relatively large resistor R1 forms a circuit that equivalently converts the output of the input voltage source Vl into an input current source.

In the above embodiment, the base-emitter junction areas of the transistors Q1 and Q2 are equal, so the input current and the output current are equal to each other, and the current gain is 1. It is clear that if the base-emitter junction area is different, a proportional current gain can be obtained.

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing an example of a conventional current amplification circuit, FIG. 2 is a connection diagram showing an example of a current amplification circuit, and FIG. 3 is a connection diagram showing an embodiment of the current amplification circuit of the present invention. Ql is a rectifying junction element, Q2 is a first transistor, Q3
is the second transistor, and Q4 and Q5 are each a diode.

Claims (1)

[Claims] 1. A first diode is connected to the base of the first transistor in the same direction as the base-emitter polarity of the first transistor, and the emitter of the first transistor and the other end of the first diode are referenced. a second transistor in series with the collector-emitter of the first transistor;
The transistors are connected so that the currents flowing through the collector emitters of the first and second transistors are almost the same, and the output current is obtained from the collector of the second transistor, and the base of the first transistor is connected. and the base of the second transistor, a second diode is connected in the same direction as the first diode so as to supply an input current to the base of the second transistor, and A current amplification circuit in which the base potential and the collector potential of the transistor are made substantially equal so that the input current and the output current are proportional to each other.