JPH0318763B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier circuit, and more particularly, to prevention of saturation of an output transistor in an amplifier circuit configured with a semiconductor integrated circuit.

FIG. 1 shows an amplifier circuit used as a conventional driver circuit. That is, this amplifier circuit is composed of a semiconductor integrated circuit, and transistors 2 and 4 are installed at its input section, and these transistors 2 and 4 constitute a current inversion circuit, so that the current applied to the input terminal 6 is inverted. and flows to transistor 4.

A current is applied to the transistor 4 via a resistor 10 from a power supply terminal 8 to which a drive voltage Vcc is applied, and current is also drawn from the base of a transistor 12 for output driving. As a result, current flows through transistor 12 and output transistor 14
A current flows through. This current flows to a load 20 connected between the output terminal 16 and the reference potential point terminal 18, and the load 20 is driven by this current.

Here, the current flowing through the load 20 is I _L , and the load 20
Assuming that the resistance value of is R _L , the voltage drop of the load 20 is given by the product of both R _L and I _L . When this voltage value increases, the output transistor 14, which is a PNP transistor, becomes saturated, and a leakage current flows from its collector toward the semiconductor substrate of the semiconductor integrated circuit, as shown by a broken line 22.

When this leakage current increases, a so-called floating potential occurs in the semiconductor substrate, and in the worst case, there is a risk that the constituent elements of the semiconductor integrated circuit may malfunction.

In particular, in integrated circuits, if it is attempted to prevent such potential floating without using an additional circuit, it is necessary to increase the area of the ground line, which causes a reduction in the degree of integration. Furthermore, leakage current increases loss in the transistor, resulting in insufficient capacity and rapid temperature rise.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an amplifier circuit that suppresses saturation of an output transistor and improves operational reliability.

That is, in the amplifier circuit of the present invention, the bases of the second transistors 4 are commonly connected to the bases and collectors of the first transistors 2 whose bases and collectors are connected in common, and the bases and collectors of the first transistors are connected in common. An input circuit that applies an input signal to the collector is installed, a power supply is connected to the collector of the second transistor of this input circuit via the first resistor 10, and the drive transistor 12 which is to drive the output transistor 14 is connected to the collector of the second transistor of the input circuit. In the base-connected amplifier circuit, an emitter E is formed on the surface layer of an epitaxial layer 36 formed on a semiconductor substrate 32, a first collector C ₁ surrounds the emitter, and a base B surrounds the first collector. and a transistor 24 formed by surrounding the base to form a second collector C ₂ is used as the output transistor, a load 20 is connected to the first collector, and a reference potential point is connected between the second collector and the reference potential point. A second resistor 26 is installed between the resistor and when the voltage drop due to the leakage current of this resistor exceeds a certain level, the leakage current from the second collector is returned to the base side of the drive transistor. diode 28
The feature is that a feedback circuit 30 consisting of the following is installed.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.

FIG. 2 shows an embodiment of the amplifier circuit of the present invention,
Components common to the amplifier circuit shown in FIG. 1 are given the same reference numerals.

In FIG. 2, first and second transistors 2 and 4 constituting a current inversion circuit are installed in the input circuit of this amplifier circuit, and the base and collector of the transistor 2 are connected in common.
Its base and collector are commonly connected to the base of transistor 4. The input current applied to input terminal 6 flows through transistor 2 and transistor 4 as well. A base current of the driving transistor 12 for driving the output transistor 24 is drawn into the transistor 4 from the power supply through the first resistor 10 . The output transistor 24 is provided with a first collector C ₁ and a second collector C ₂ for detecting its leakage current. The first collector C ₁ forms an output terminal 16 and a load 20
Connect. Further, a second resistor 26 is connected between the second collector C ₂ and a common line connected to the reference potential point through the reference potential point terminal 18, and a second resistor 26 is connected between the second collector C ₂ and the common line connected to the reference potential point through the reference potential point terminal 18. A diode 2 is connected between the base of the transistor 12 and the base of the transistor 12.
8 are connected to form a feedback circuit 30.
That is, a voltage drop occurs in the diode 28 due to the leakage current, and this voltage drop is caused by the diode 28.
If the forward voltage drop _VF is exceeded, the leakage current is fed back to the base side of the transistor 12.

3 and 4 show examples of integrated circuit configurations of the transistor 24, with FIG. 3 showing the planar structure thereof, and FIG. 4 showing a cross section taken along the line - in FIG. 3.
That is, after forming, for example, an N-type buried layer 34 on the semiconductor substrate 32 in the region where the transistor 24 is to be formed, the epitaxial layer 36 is formed, and the region where the transistor 24 in this epitaxial layer 36 is to be formed is separated by the isolation region 37. It is divided into sections. In the divided epitaxial layer 36, P-type diffusion regions 38, 40, and 42 are formed, and an N-type diffusion region 44 is further formed. Diffusion region 38 is emitter E, diffusion region 40 is first collector C ₁ , diffusion region 42 is second collector C ₂ , diffusion region 44
constitutes base B. An oxide film 46 is formed on the surface layer, and contact holes 48 are formed in each region. Although not shown, a wiring conductor made of aluminum or the like is connected to the contact hole 48.

The operation will be explained based on the above configuration. When a leakage current flows through the transistor 24, this leakage current flows from the second collector _C2 to the resistor 26.
Resistor 26 detects this leakage current as a voltage drop. When this voltage drop exceeds the forward voltage drop V _F of the diode 28 , a leakage current flows through the diode 28 and flows into the transistor 4 . Due to the feedback of this leakage current, the base current of transistor 12 is reduced by the leakage current of transistor 24.
As a result, the input base current of transistor 24 is reduced, its output current is suppressed, and saturation is prevented.

Further, as a result of preventing leakage current to the semiconductor substrate 32, floating of the potential of the semiconductor substrate 32 can be prevented, and there is no problem such as increasing the area of the ground line.

As explained above, according to the present invention, the leakage current of the output transistor is detected by the second collector installed outside the first collector with the base interposed, and the leakage current is detected from the diode. By feeding back to the base of the driving transistor of the output transistor through a feedback circuit consisting of
Since the input current is controlled according to the leakage current, saturation of the output transistor can be prevented, and the potential of the semiconductor substrate can be prevented from floating due to the leakage current, thereby increasing the reliability of operation.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing a conventional amplifier circuit, Figure 2 is a circuit diagram showing an embodiment of the amplifier circuit of the present invention, Figure 3 is a plan view showing the configuration of an output transistor, and Figure 4 is its cross-sectional configuration. FIG. 2...First transistor, 4...Second transistor, 10...First resistor, 12...Drive transistor, 14, 24...Output transistor, 20...Load, 26...Second transistor Resistance, 28...
...Diode, 30...Feedback circuit, 32...Semiconductor substrate, 36...Epitaxial layer.

Claims (1)

[Claims] 1. The bases of second transistors are commonly connected to the bases and collectors of the first transistors whose bases and collectors are commonly connected, and an input signal is connected to the bases and collectors of the first transistors. An input circuit is installed to add the second input circuit.
In an amplifier circuit in which a power supply is connected to the collector of a transistor via a first resistor and the base of a driving transistor that drives an output transistor is connected, an emitter is connected to the surface layer of an epitaxial layer formed on a semiconductor substrate. , a transistor having a first collector surrounding the emitter, a base surrounding the first collector, and a second collector surrounding the base is used as the output transistor; Connect the load to the collector of 1,
A second resistor is installed between the second collector and the reference potential point, and when the voltage drop due to the leakage current of this resistor exceeds a certain level, the leakage current from the second collector is An amplifier circuit characterized by installing a feedback circuit consisting of a diode that feeds back to the base side of a driving transistor.