JPH05152910A - Comparator - Google Patents

Abstract

PURPOSE:To prevent a current difference from being supplied to the base of an output transistor(TR) entirely and to quicken a reply speed by providing an input section supplying a current in response to two input voltages and an output section having a current mirror circuit at its output on a comparator. CONSTITUTION:A current in response to the input of TRs 2, 3 flows to TRs 4, 5. The TRs 4, 5 form a current mirror circuit and the same current flows to both TRs. When there is any difference between currents flowing to the TRs 2, 3, the difference is supplied or absorbed by a current mirror circuit composed of the TRs 6, 7. When the current flows to the TR 6, the output TR 7 absorbs the output current and when a current is absorbed from the output section, the output TR 7 reaches a high impedance. Since the output section is the current mirror circuit composed of the TRs 6, 7, the difference current is not entirely supplied to the base of the output TR 7. Thus, no time is required for the output inversion and the response time is shortened.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a comparator,
In particular, it relates to a bipolar transistor comparator.

[0002]

2. Description of the Related Art In a conventional comparator, as shown in FIG. 2, the output portion has only a single transistor.

Next, the operation will be described. The two inputs are amplified by transistors 2 and 3, respectively. The sum of the amplified currents becomes the output of the constant current source 1. The amplified currents flow into the transistors 4 and 5, respectively. Since the transistors 4 and 5 are current mirror circuits, the same current as the current flowing through the transistor 4 flows through the transistor 5. Therefore, when the current flowing through the transistor 3 is larger than the current flowing through the transistor 2, the transistor 5 alone cannot flow and the current flows into the base of the transistor 8. This is the state where the output current is being absorbed. If the current flowing through the transistor 2 is larger than the current flowing through the transistor 3, the current does not flow into the transistor 8 and the output becomes high impedance.

[0004]

This conventional comparator circuit has a problem that it takes a long time for the output to invert because the difference in the current is supplied to the output transistor, and the response speed is slow. .

[0005]

The comparator of the present invention comprises an input section for supplying a current according to the voltage of each of the two inputs, and an output section having a current mirror circuit.

[0006]

The present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of an embodiment of the present invention. A current corresponding to the input of the transistors 2 and 3 flows into the transistors 4 and 5. Since the transistors 4 and 5 are current mirror circuits, the same current flows through the transistors 4 and 5. Therefore, if there is a difference in the currents flowing through the transistors 2 and 3, the difference flows into or is absorbed by the current mirror circuit of the transistors 6 and 7. When the current flows into the transistor 6, the output transistor 7 absorbs the output current, and when the current is drawn from the output section, the output transistor 7 becomes high impedance.

Since the output portion is a current mirror circuit composed of the transistors 6 and 7, all the differential current does not flow into the base of the output transistor 7.

[0008]

As described above, since the present invention has the current mirror circuit in the output section, it takes no time for the output to be inverted because the difference in current does not flow into the base of the output transistor. Therefore, there is an effect that the response time is shortened.

[Brief description of drawings]

FIG. 1 is a circuit diagram of the present invention,

FIG. 2 is a circuit diagram of a conventional circuit.

[Explanation of symbols]

 1 constant current source 2 input transistor 3 input transistor 4 current mirror transistor 5 current mirror transistor 6 output section current mirror transistor 7 output transistor 8 output transistor

Claims (1)

[Claims] 1. A comparator comprising an input section for supplying a current according to the voltage of each of two inputs and an output section having a current mirror circuit in the output section.