JPH0262106A - Operational amplifier - Google Patents

Abstract

PURPOSE:To obtain a sufficient output voltage for operation by outputting from a positive power source to an output terminal, when the output voltage is positive, by a first current mirror circuit and outputting from an output edge terminal to a negative power source by a second current mirror circuit when the output voltage is negative. CONSTITUTION:By the function of a polarity identifying circuit, and when the output electric power positive, by the function of a first current mirror circuit 9, the current flows from a supply voltage VDD to an output terminal. When the output voltage is negative, the current flows from output terminal to a negative input terminal VSS by the function of a second mirror circuit. When the potential of a positive input terminal 1 is higher than the potential of a negative input terminal 2, a transistor TR Q15 is conducted, TR Q17 is off and an output terminal 3 is lifted up to a positive supply voltage VDD side. At this time, TR Q7 is on, and through a resistance R16 to the circuit 9, the current flows. At the collector of TR Q22, the current of the product of the emitter area ratio of TR Q21 and Q22 and the collector current of TR Q21 flows, and the output terminal 3 is also lifted up to a VDD side. In the same way, when the potential of the negative input terminal 2 is higher than the potential of the terminal 1, the output is shifted to the VSS side.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to an operational amplifier used in an integrated circuit, and particularly to an operational amplifier whose output voltage can be varied from a positive power supply voltage to a negative power supply voltage. Regarding amplifiers.

Conventional technology An example of a conventional operational amplifier circuit is shown in FIG.

In FIG. 2, Q1 to Q, 8. R, ~R++ are transistors and resistors that form the operational amplifier; 1 is the (→input terminal), 2 is the (c) input terminal, 3 is the output terminal, 4 is the positive power supply terminal (hereinafter abbreviated as "vDD"), 5 is a negative power supply terminal (hereinafter abbreviated as "vss"), 6 is a ground terminal (hereinafter GN
(abbreviated as D).

Problems to be Solved by the Invention In such a conventional operational amplifier, the possible voltage range of the output terminal 3 is Vn = vnn (vcxSatQ7+VagQ+
s) from vL = vSS + vax”tQ1
6+VBzQ17

However, Vo and sat mean the saturation voltage between the collector and emitter of the transistor, and vBx means the forward voltage drop between the base and emitter.

If VC,sat is 0.2V and Vo is 0.7V, the output voltage of the conventional operational amplifier is V,D-0,9''/
From vss + 0.9 V
, vss. When the voltage is low, a sufficient output voltage may not be obtained.

The present invention is intended to solve such problems, and aims to enable a sufficient output voltage to be obtained even when the power supply voltage is low.

Means for Solving the Problems The technical means of the present invention for solving the above problems are as follows: The emitters of the second transistors are respectively connected to the ground terminal, and both bases are connected to the output terminal via a resistor, and when the output voltage is positive with respect to the ground potential, the first transistor conducts, and when the output voltage is negative, the second transistor conducts. a first current mirror circuit connected to the collector of the first transistor via a resistor and mirroring the collector current of the first transistor with respect to a positive power supply voltage; A second transistor is connected to the collector of the second transistor via a resistor and mirrors the collector current of the second transistor with respect to the negative power supply voltage.
a current mirror circuit; The output side terminal of the second current mirror circuit is connected to the output terminal.

Operation With this configuration, in a normal operational amplifier, the output voltage varies from vno 0.9V to vss as explained in the conventional example earlier.
Although it can only output up to +0.9 V, when the output voltage is positive due to the function of the polarity identification circuit, current flows from VDD to the output terminal due to the function of the first current mirror circuit. Further, when the output voltage is negative, a current flows from the output terminal toward vs8 due to the action of the second current mirror circuit. If the impedance of the load connected to the output terminal is large and the load current is smaller than the output currents of the first and second current mirror circuits, the output terminal voltage can be output from approximately vDI to VSS.

Example An embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, elements having the same functions as those in FIG. 2 are denoted by the same reference numerals, and explanations thereof will be omitted. Reference numeral 8 indicates a first transistor constituting a polarity identification circuit, 8 a second transistor, 9 a first current mirror circuit, and 1Q a second current mirror circuit. (a) When the potential of input terminal 1 is higher than the potential of input terminal 2, transistor Q+5
is conductive (hereinafter referred to as ON), transistor QI7 is cut off (hereinafter referred to as OFF), and the output terminal 3 rises to the VD side. At this time, the first transistor 7 is turned on, and current flows through the first current mirror 9 through the resistor R.

Transistor Q2+ is connected to the collector of transistor Q2□.
Since a current equal to the product of the ratio of the emitter area of , the emitter area of transistor Q22, and the collector current of transistor Q)H will flow, if the output terminal 3 is further raised to the VDD side and the load impedance is large, the output terminal voltage will be v.
DD-vOIIQ2□#vDD. Similarly (c)
When the potential of the input terminal 2 is higher than the potential of the input terminal 1 (a), the transistor Qj7 is OWL.The transistor Q+5 is turned off, and the output terminal voltage becomes the vss side. A current flows through the current mirror 10 through the resistor R47, and 4
Output terminal 3 due to the collector current of transistor Q25.
The voltage can be lowered to approximately VSS.

Note that when negative feedback is added to this operational amplifier to make it a linear amplifier, the operation is such that when the voltage at the output terminal 3 is on the VDD side, the emitter current of the transistor Qj7 absorbs the collector current of the transistor Q2□, and the output terminal voltage is controlled linearly. be done. Furthermore, when the voltage of the output terminal 3 is on the vss side, the collector current of the transistor Q25 is changed to the transistor Qi5.
emitter current is controlled, and the output terminal voltage is linearly controlled.

Effects of the Invention As described above, the present invention has the advantage that the output terminal voltage varies from vDD to vs
It can be an operational amplifier capable of outputting any voltage up to s.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an operational amplifier according to an embodiment of the present invention, and FIG.
The figure is a circuit diagram of a conventional operational amplifier. 1...(A) Input terminal, 2...(C)
Input terminal, 3... Output terminal, 4... Plus power terminal (vDD), 6... Negative power terminal (vss), 6... Ground terminal, End... ...First
transistor, 8... second transistor, 9.
...°・First current mirror 10...Second
current mirror of

Claims (1)

[Claims] The emitters of the first and second transistors having different polarities are connected to the ground terminal, and both bases are connected to the output terminal via a resistor, and when the output voltage is positive with respect to the ground potential, the first transistor is conductive. and a first current connected to the collector of the first transistor via a resistor to mirror the collector current of the first transistor with respect to the positive power supply voltage. a mirror circuit, and a second transistor connected to the collector of the second transistor via a resistor to mirror the collector current of the second transistor with respect to the negative power supply voltage.
an operational amplifier, comprising: a current mirror circuit; and the output terminals of the first and second current mirror circuits are connected to the output terminal.