JPS624884B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an input circuit for a bipolar semiconductor circuit, and more particularly to an improvement in the input circuit in which the input current flowing from the input signal source is kept constant.

In bipolar semiconductor circuits that accept signals from various signal sources, input circuits using bipolar transistors are used to prevent input signals from being overloaded by the signal sources and impairing input signal accuracy.

Figure 1 is a circuit diagram showing a conventional example of such an input circuit, where 1 and 2 are input terminals, 3 and 4 are common collector PNP transistors whose bases are connected to input terminals 1 and 2, respectively, and 5 is a power supply. terminal, 6
and 7 are drain-type current sources connected between the emitters of transistors 3 and 4, respectively, and the power supply terminal 5; 8 and 9, whose bases are connected to the emitters of transistors 3 and 4, respectively, and whose emitters commonly sink current sources; grounded via source 10
The npn transistors 11 and 12 are pnp transistors whose collectors are connected to the collectors of transistors 8 and 9, respectively, whose bases are connected to each other, and whose emitters are both connected to the power supply terminal 5.
The base and collector of the transistor 11 are short-circuited to form a diode connection.

Since there is no need to explain the operation of this circuit, the explanation will be omitted, but the currents of constant current sources 6 and 7 are both I ₁ , the current of constant current source 9 is I ₀ , and the base current of transistors 8 and 9 is I _B1 , the base currents of transistors 3 and 4 are I _B2 , then the current I ₁ and the current I _B1 are set to have the following relationship.

I _B1 ≪I ₁ [1] Also, the current amplification factor of transistors 3 and 4 (pnp
When the transistor current amplification factor) is h _FEp , the circuit input current I _B2 is expressed as I _B2 = (I ₁ - I _B1 )/h _FEp . However, since I ₁ >>I _B1 from equation [1], the input current I _B2 is expressed as I _B2 ≈I ₁ /h _FEp . As described above, there is a drawback that the input current varies greatly depending on the magnitude of the current amplification factor _hFEp of the input transistor.

This invention was made in view of the above points, and by using a current mirror circuit instead of a transistor similar to the input transistor and a fixed current source, the current amplification factor of the input transistor can be changed. The purpose of this invention is to provide an input circuit in which the input current is constant even when the input current is constant.

FIG. 2 is a circuit diagram showing an embodiment of this invention.
The same reference numerals as in the conventional example in FIG. 1 indicate equivalent parts. 1
3 is a multi-collector PNP transistor whose emitter is connected to a power supply terminal 5 and whose two collectors are connected to the emitters of input transistors 3 and 4, respectively. 14 has an emitter area of transistor 1
3, a pnp transistor 1 whose base and collector are both connected to the base of the transistor 13 and whose emitter is connected to the power supply terminal 5;
5 is a pnp transistor whose emitter is connected to the collector of the transistor 14, whose collector is directly grounded, and whose base is grounded via a sink type constant current source 16.

Transistor 15 and transistors 3 and 4 are formed on the same chip and in the same shape, and have the same current amplification factor _hFEp . Let the current of the suction type constant current source 16 be _I2 . Transistors 13, 14, and 15 constitute a current mirror circuit, and by sinking the base current of transistor 15 with a sink type constant current source 16, the emitter of transistor 15,
and I ₂ in the diode-connected transistor 14.
×h A current of _FEp flows. Therefore, when the emitter areas of transistors 13 and 14 are equal, the total collector current of transistor 13 is equal to I ₂ ×h _FEp due to the current mirror principle, and I ₂ is applied to each collector, that is, the emitter of transistors 3 and 4, respectively. A current of ×h _FEp /2 flows. Here, as mentioned above, transistors 15, 3 and 4 have the same current amplification factor h _FEp , so the input current I _B2 to the bases of transistors 3 and 4 is I _B2 = I ₂ ×h _FEp /2/h _FEp =I ₂ 2 and becomes a constant value of 1/2 of the current of the sink type constant current source 16. Therefore, even if the current amplification factor varies due to the manufacturing process of the integrated circuit, the input current is kept constant without being affected by the variation.

Note that in the above embodiment, the input transistors 3,
Although 4pnp transistors were used, an npn transistor may also be used, and in this case transistor 1
A similar effect can be obtained by using an npn transistor in 5 and by making the constant current source 16 into a constant current source. Furthermore, it goes without saying that the input transistors may be Darlington connected.

As explained above, in the input circuit according to the present invention, the current of the transistor of the input circuit is regulated by the current mirror circuit, and the current determining transistor of the mirror circuit is made to have the same current amplification factor as the input transistor. The input current flowing to the base of the input transistor can be kept constant without being affected by the current amplification factor of the transistor.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional input circuit.
FIG. 2 is a circuit diagram showing an embodiment of the present invention. In the figure, 1 and 2 are input terminals, 3 and 4 are first and second input transistors, respectively, and 5
is a power supply terminal, 13 is a multi-collector transistor, 14 is a diode-connected transistor, 15
1 is a constant current supply transistor, and 16 is a constant current source. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1 First and second PNP (or NPN) type input transistors with differential input signals directly input to their respective bases and each collector (or emitter) grounded, emitters connected to the power supply terminal and two collectors A multi-collector PNP transistor connected to the emitter (or collector) of the first and second input transistors, each having an emitter region of the same area as the emitter region of the multi-collector transistor; A diode-connected PNP transistor connected in parallel between the emitter and base of the transistor, and the emitter is connected to the base of the multi-collector transistor and the base and collector of the diode-connected transistor, and the collector is grounded. A constant current source is connected between the base and the ground point, and a pnp (or npn) type transistor for constant current supply having a current amplification factor equal to that of the first and second input transistors is provided. input circuit.