JPH03190318A - voltage comparator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a voltage comparator with a small input bias current.

BACKGROUND OF THE INVENTION A voltage comparator is an important part of an analog-to-digital converter that determines the accuracy of the product, and the accuracy of the voltage comparator has a factor that deteriorates the accuracy of the product.

A conventional voltage comparator will be explained below.

FIG. 2 shows a conventional voltage comparator.

In Figure 2, 1 is a ground electrode, 2 is a first power supply terminal, 4 and 5 are input terminals, 6 and 7 are output terminals, 8 and 9
is a resistor, 10 and 11 are NPN transistors, and 14 is a current source.

The operation of the voltage comparator configured as above will be described below.

First, when a voltage sufficiently higher than the voltage at the input terminal 5 (usually about 100 mV) is applied to the input terminal 4, a current approximately equal to the current source 14 flows through the collector of the NPN transistor 10. The NPN transistor 11 is then cut off and no current flows through its collector. At this time, both ends of the resistor 8 connected to the collector of the NPN transistor 10 are
A voltage equal to the product of the resistor 8 and the current value of the current source 14 is generated.

On the other hand, since no current flows across the resistor 9, no potential difference occurs. As a result, a potential difference equal to the product of the resistor 8 and the current value of the current source 14 is generated between the output terminals 6 and 7. As described above, the input voltages at input terminals 4 and 5 can be compared and amplified. Further, when a voltage sufficiently higher than the voltage at the input terminal 4 is applied to the input terminal 5, a potential difference equal to the product of the resistor 9 and the current value of the current source 14 is generated between the output terminals 6 and 7.

Problems to be Solved by the Invention However, in the above conventional example, when the emitter current of the NPN transistor 10 or 11 flows, approximately the emitter current is used as the base current of the NPN transistor 10.
Or a current divided by hFE of 11 flows. Therefore, there is a drawback that current is drawn from the input terminal 4 or 5, which affects the circuit connected to the input terminal 4 or 5.

The present invention solves the above-mentioned conventional problems, and aims to provide a voltage comparator in which no bias current flows through the input terminal.

Means for Solving the Problems To achieve this object, the voltage comparator of the present invention provides a P-type MOS transistor and a current source in a conventional voltage comparator, thereby converting the base current of a conductive NPN transistor into a current. It has a configuration in which it is supplied from a source via a P-type MOS transistor.

Effect: With this configuration, the base current that flows when the NPN transistor is turned on is compensated by the drain current of the P-type MO3I transistor, and it is possible to eliminate the inflow of current from the input terminal.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of a voltage comparator in one embodiment of the present invention. In Figure 1, 1 (Yo ground electrode, 2
is the first power supply terminal, 3 is the second power supply terminal, 4 and 5 are input terminals, 6 and 7 are output terminals, 8 and 9 are resistors, 10 and 11 are NP
N transistors, 12 and 13 are P-type MOS transistors, and 14 and 15 are current sources.

The operation of the voltage comparator configured as above will be described below.

First, when a voltage sufficiently higher than the voltage at input terminal 5 is applied to input terminal 4, NPN transistor 10 becomes conductive and NPN transistor 11 is cut off. At that time NP
The emitter current of N transistor 10 is determined by current source 14. The value obtained by subtracting the voltage value determined by the product of this emitter current and the resistor 8 from the potential of the first power supply terminal 2 is the value at the output terminal 6.
The output voltage will be . When an emitter current flows, a value approximately equal to the emitter current divided by hFE of the NPN transistor 10 flows from the input terminal 4 as a hese current of the NPN transistor 10. In this state, the potential of the output terminal 6 is lower than the power supply voltage of the first power supply terminal 2, so the P-type M
The gate voltage of the OS transistor 12 decreases and the P-type MOS
Transistor 12 becomes conductive. At this time, as the base current compensation value of the NPN transistor 10, the value of the current source 15 and the current value of the current source 14 are set as the base current compensation value of the NPN transistor 10.
Set it equal to the current value divided by FE. This means that
This means that the base current of the NPN transistor 10 is not supplied from the input terminal 4 but from the current source 15 via the P-type MO3I transistor 12.

As described above, according to this embodiment, by providing the P-type MOS transistors 12 and 13 and the current source 15, the base current of the NPN transistor 10 in the conductive state is
5 through the P-type MOS transistor 12, so that no current flows to the input terminal 4.

Furthermore, in this embodiment, it is clear that the same operation occurs even when the voltage of the input terminal 5 is sufficiently higher than that of the input terminal 4, and the NPN transistor is replaced with a PNP transistor, and the P-type MO3+- transistor is replaced with an N-type MOS transistor. Needless to say, it can be done using the same idea.

Effects of the Invention As described above, the present invention provides an excellent voltage comparator with a base current compensation circuit that does not draw the base current of the transistor from the input terminal by providing a MOS transistor and a current source in a conventional voltage comparator. It is possible to realize a comparator.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a voltage comparator according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional voltage comparator. 1... Ground electrode, 2... First power terminal, 3... Second power terminal, 4.5... Input terminal, 6.7. ...Output terminal, 8.9...
...Resistance, 10.11...NPN transistor, 12.13...P-type MOS transistor, 1
4.15...Current source. Man 1 picture palace 9 Figure 1 Seifukudento 2 or 1 source jlf 1 multi 38 2 electricity: ft, Btn child 4.5 x or Kashimako 6.7 out rJ Tomojima da

Claims (1)

[Claims] a first transistor having a collector electrode connected to a first power supply terminal via a first resistor and a base electrode connected to a first input terminal; a second transistor connected to the power supply terminal and having its base electrode connected to the second input terminal; a first current source having one end coupled to the emitter electrodes of the first and second transistors; and a drain electrode. is connected to the first input terminal, and has a gate electrode connected to the collector electrode of the first transistor; a first MOS transistor, whose drain electrode is connected to the second input terminal, and whose gate electrode is connected to the collector electrode of the first transistor; A voltage comparator comprising a second MOS transistor connected to a collector electrode of the second transistor, and a second current source having one end coupled to the source electrodes of the first and second MOS transistors.