JPH05102807A - Comparator - Google Patents

Abstract

PURPOSE:To provide the comparator comparing an input current with a reference current and outputting the result of deciding the quantity. CONSTITUTION:A constant current source 3 supplying a current I1 proportional to an input current Iin and a constant current source 4 supplying a reference current Ir are connected in series with resistive loads R1, R2 and the comparison between the input current Iin and the reference current Ir is implemented by comparing voltage drops across the two resistors. The power consumption is reduced by supplying a current as required by inserting switches 9, 10 in series between the constant current source 3 and the resistive load R1 and between the constant current source 4 and the resistive load R2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a comparator, and more particularly to a comparator that compares an input current and a reference current to determine the magnitude relationship.

[0002]

2. Description of the Related Art Conventionally, as a comparator, a voltage comparator is generally used which compares an input voltage with a reference voltage and judges the magnitude relation. A circuit diagram of an example of such a conventional comparator is shown in FIG. This comparator is based on the IE Journal of Solid State Circuits (IEEE).
E Journal of Solid-stateC
ircuits), SC-20, 1985, 3rd.
No., page 775.

This comparator compares the magnitude relationship between the input voltage and the reference voltage, and outputs Q = "1" as the output Q when the input voltage is larger, and outputs Q when the reference voltage is larger. This is a comparator that outputs = “0”. This comparator is
The differential amplifier that amplifies the difference between the analog input voltage and the reference voltage and the comparison unit that determines the magnitude relationship between the two inputs perform the following operation. First, the differential amplifier amplifies the difference between the input voltage applied to the differential input terminal and the reference voltage and transmits the amplified differential signal to the comparison unit in the next stage. In the comparison section, V _{1 in} the figure is changed to V ₂ in accordance with the magnitude relation of the transmitted differential signals
If it is smaller than, output "1" as digital output,
If V ₁ is larger than V ₂ , “0” is output. Therefore, this comparator is a comparator that outputs "1" when the input voltage is higher than the reference voltage and outputs "0" when the input voltage is lower than the reference voltage.

[0004]

The voltage comparator for comparing the input voltage and the reference voltage as in the prior art has the following problems when the LSI is considered.

When the power supply voltage of the LSI decreases with the development of the LSI technology, the input range or the input dynamic range decreases.

A signal-to-noise ratio (S / N ratio) deteriorates with a decrease in input dynamic range.

When all signals are handled in the form of voltage, noise voltage due to capacitive coupling between power supply wiring and signal wiring causes
Accuracy deteriorates. With the miniaturization of LSI, the capacitive coupling is increasing, and the accuracy is getting worse.

[0008]

The comparator of the present invention comprises a first comparator.
A first resistance load whose one end is connected to the constant voltage source, and a first resistance load, which is connected between the other end of the first resistance load and the second constant voltage source and flows a current proportional to the input current. A constant current source, a second resistance load whose one end is connected to the first constant voltage source, and a reference current which is connected between the other end of the second resistance load and the second constant voltage source. And a second constant current source for flowing a current, and a comparison unit for outputting the result of comparing the potential of the other end of the first resistive load and the potential of the other end of the second resistive load to determine the magnitude relationship. It consists of and.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an optimum embodiment of the present invention will be described with reference to the drawings. FIG. 1A is a circuit diagram of the first embodiment of the present invention. Referring to FIG. 1A, this comparator has a first resistive load R ₁ whose one end is connected to a first constant voltage source 1, another end of the first resistive load R ₁ and a second resistive load R ₁ . A first constant current source 3 connected between the constant voltage source 2 and a current I _I proportional to the input current I _in , and a second resistive load R2 having one end connected to the first constant voltage source And the second resistive load R
_{The second} constant current source 4 connected between the other end of 2 and the second constant voltage source 2 and flowing the reference current I _r , and the potential V _{1 at} the other end of the _first resistive load R ₁ and the second Potential V _{2 at} the other end of the resistive load R ₂ of
And a comparator 5 that outputs the result of the determination of the magnitude relation to the output end 6 of the comparator 5.

2 (a) to 2 (c) show an example of the structure of the constant current source 3 which supplies a current proportional to the input current I _in . Figure 2
(A) shows what was comprised by the current mirror circuit of a MOS transistor. FIG. 2B shows a configuration in which current mirror circuits are vertically stacked in two stages. FIG. 2C shows a configuration in which an active feedback type gate ground circuit is used on the output side of the current mirror circuit. Figure 2
Also in the circuit of (a) ~ (c) the throat, MOS transistors ratio of the current flowing through the current and MOS transistor M ₂ through the M _1, the ratio W of the MOS transistor M channel width W ₁ of ₁ and the channel length L _{1 1} / L ₁ and, MOS transistor channel width of M ₂ W ₂ and the channel length L ₂
The ratio between the ratio W ₂ / L ₂ of _{(W 1 / L 1) /} (W 2 / L 2)
Is proportional to. Therefore, a current I _I having a magnitude proportional to the input current I _in input from the input end 7 is supplied to the output end 8
Can be poured from.

The constitution of the constant current source 4 for supplying the reference current I _r is also as follows.
By using the reference current Ir _in place of the input current I _in shown in FIGS. 2A to 2C, the constant current source 3 can be realized with the same configuration.

The resistive loads R ₁ and R ₂ are shown in FIG.
Besides using the resistor shown in (a), a MOS transistor can be used as a substitute for the resistor as shown in FIG. 1 (b).

The comparison unit 5 has a function of determining the magnitude relationship between two inputs. An example of the configuration is shown in FIG.

With the simple configuration described above, the comparison between the input current and the reference current can be executed, and the result of determining the magnitude relationship can be obtained as an output.

Next, a second embodiment of the present invention will be described. FIG. 4 is a diagram showing a circuit diagram of the second embodiment of the present invention. Referring to FIG. 4, this comparator is shown in FIG.
Compared with the comparator shown in FIG. 1, the first switch 9 is connected in series between the first resistance load R ₁ and the first constant current source 3, and the second resistance load R ₂ and the second constant load R ₂ are connected in series. The difference is that a second switch 10 is connected in series with the current source 4. FIG. 4 shows an example in which the switches 9 and 10 are composed of MOS transistors.

The functions of the switches 9 and 10 are to control the opening and closing of the current path for flowing the current I _I and the current path for flowing the reference current I _r, which are proportional to the input current I _in , by the switches 9 and 10, respectively. .. That is, no current flows through the circuit when switches 9 and 10 are open, and current flows through the circuit only when switches 9 and 10 are closed. Therefore, by closing the switch only when necessary and allowing the current to flow through the circuit and opening the switch when not needed to interrupt the current, the power consumption can be reduced as compared with the case where the current is always applied through the circuit. For example, it suffices to allow the current to flow only when the comparison is performed, and if the time when the switch is closed and the time when the switch is open are the same, the power consumption can be reduced to 1/2. However, as compared with the comparator shown in FIG. 1A, the number of elements increases by the amount of the switches 9 and 10, so the comparator having the configuration shown in FIG. Whether to use the comparator having the configuration depends on which of power consumption reduction and the number of elements is prioritized.

[0017]

As described above, according to the present invention, there is provided a comparator having a simple structure capable of obtaining the output as a result of comparing the input current and the reference current and determining the magnitude relationship. I can do things.

[Brief description of drawings]

FIG. 1A is a circuit diagram of an example of a comparator according to a first embodiment of the present invention. FIG. 6B is a circuit diagram of another example of the comparator according to the first embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of a circuit configuration of constant current sources 3 and 4 in FIG.

FIG. 3 is a circuit diagram showing an example of a circuit configuration of a comparison unit in FIG.

FIG. 4 is a circuit diagram of a comparator according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram of an example of a conventional voltage comparator.

[Explanation of symbols]

 1, 2 constant voltage source 3, 4 constant current source 5 comparison part 6, 8 output end 7 input end 9, 10 switch

Claims (2)

[Claims] 1. A first one having one end connected to a first constant voltage source.
Constant resistance source, a first constant current source connected between the other end of the first resistance load and the second constant voltage source, and flowing a current proportional to the input current, and the first constant voltage source A second resistance load whose one end is connected to the second resistance load; a second constant current source connected between the other end of the second resistance load and the second constant voltage source to flow a reference current; A comparison unit configured to compare the electric potential at the other end of the first resistive load with the electric potential at the other end of the second resistive load and output the result of determining the magnitude relationship, vessel. 2. The comparator according to claim 1, wherein a first switch is connected in series between the first resistance load and the first constant current source, and the second resistance load and the second switch are connected in series. A second switch is connected in series between the second constant current source and the second constant current source.