JPH10197572A - Hysteresis comparator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce electric power consumption by respectively connecting short-circuit means to a power source side resistance and a grounding side resistance of a reference power source generating circuit, short-circuiting the short-circuit means by a short-circuit signal from a comparator, and generating hysteresis. SOLUTION: An FET 1 and an FET 2 being short-circuit means are respectively connected to both ends of a power source side resistance R31 and a grounding side resistance R34 of a reference voltage generating circuit, and both gates of the FETs 1 and 2 are connected to the output end of a comparator 3, By constituting these in this way, the FETs 1 and 2 mutually and inversely operate according to output of the comparator 3, and generate hysteresis by short-circuiting respective both ends of resistances 31 and 34. Therefore, a constant current source to generate the hysteresis is not required, and since there is no large change in a resistance value caused by generation of the hysteresis, electric power consumption can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hysteresis comparator, and more particularly, to a reduction in power consumption of a hysteresis comparator.

[0002]

2. Description of the Related Art A technique for generating hysteresis in a comparator has been known (Japanese Patent Laid-Open No. 58-182).
560, etc.). FIG. 3 shows a circuit configuration of such a conventional hysteresis comparator. In this hysteresis comparator, the switches S11 and S12 operate in opposite directions to each other according to the output of the comparator (hereinafter, referred to as "COMP") 1. The signal under test is input to COMP1 via the input terminal IN.

When the signal level of the signal under test input via the input terminal IN is equal to or lower than the low threshold value (Lo level), the output of COMP1 becomes Hi level, the switch S11 is turned on, and the switch S12 is turned off. . Then, the constant current I is supplied from the constant current source CS11 to the resistor R12,
The reference voltage V _A of the OMP 1 (the voltage at the connection point A) becomes the high threshold value VthH represented by the following equation, and enters a stable state.

VthH = R12 × (Vcc + R11 × I) / (R11 + R12) IccH = (Vcc + R11 × I) / (R11 + R12) Next, the signal level of the signal under measurement is higher than the high threshold ( (Hi level), the output of COMP1 becomes Lo level, switch S11 is OFF, and switch S12 is ON.
Becomes The constant current supply from the constant current source CS11 to the resistor R12 is cut off, and the constant current I is supplied to the resistor R11 by the constant current source CS12. The reference voltage V _A becomes a stable state in the low-threshold VthL represented by the following formula.

VthL = R12 × (Vcc-R11 × I) / (R11 + R12) IccL = (Vcc + R12 × I) / (R11 + R12) In addition, current consumption Iref without hysteresis, and hysteresis are added. The current consumption increase Ihys at this time is expressed by the following equation. Iref = Vcc / (R11 + R12) Vhys = 2 × R11 × I / (R11 + R12) Ihys = IccH-Iref = R11 × I / (R11 + R12) = (1 / (2 × R12)) × Vhys ( (Comp output Hi) Ihys = IccL-Iref = R12 × I / (R11 + R12) = (1 / (2 × (R11)) × Vhys (Comp output Lo) Thus, this conventional hysteresis comparator In the above, a hysteresis characteristic is generated in a reference voltage using a constant current source.

Incidentally, the hysteresis comparator is:
Although it is often incorporated in an integrated circuit or the like using a dry cell, a battery, or the like as a power source, such a hysteresis comparator requires low power consumption. In the conventional hysteresis comparator, as shown in FIG. 4, the current consumption Icc increases as compared with a comparator having no hysteresis characteristics. Then, the increased consumption current Ihys increases in proportion to the hysteresis width Vhys.

FIG. 5 shows an example of a hysteresis comparator in which this point is improved. This hysteresis comparator has only one switch S2, and this switch S2 is turned on when the output of COMP2 is at Hi level and turned off when the output of COMP2 is at Lo level.

[0008] When the signal level of the measured signal is below the low threshold, the output of COMP2 becomes Lo level, the switch S2 is turned OFF, the V _B (voltage at the connection point B) reference voltage COMP2, the following equation High threshold Vt expressed by
hH, and becomes a stable state. VthH = Vcc × (R22 + R23) / (R21 + R22 + R23) IccH = Vcc / (R21 + R22 + R23) Next, when the signal level of the signal under measurement changes above the high threshold, COMP2 the output becomes Hi level, the switch S2 is turned ON, the reference voltage V _B becomes a stable state in the low-threshold VthL represented by the following formula.

VthL = Vcc × R22 / (R21 + R22) IccL = Vcc / (R21 + R22) Note that the current consumption Iref without the hysteresis circuit is
The hysteresis width Vhys and the increase in current consumption Ihys due to the provision of the hysteresis generation circuit are expressed by the following equations.

Iref = Vcc / (R21 + R22 + R23) Vhys = R21 × R23 × Vcc / ((R21 + R22 + R23) × ((R21 + R22)) Ihys = IccH−Iref = 0 (when COMP output is Hi Ihys = IccL−Iref = (1 / R21) × VhyS (when COMP output is low) As described above, the hysteresis comparator as shown in FIG. 5 does not require a constant current source for generating hysteresis and outputs the COMP output. The increase in power consumption at the time of Hi is cut, and power consumption is reduced.

[0011]

However, even in such a conventional hysteresis comparator, when the voltage dividing ratio of the voltage dividing resistor of the reference voltage generating circuit is changed (COMP output Lo).
At the same time, at the same time, the combined resistance of the voltage dividing resistors is greatly reduced, so that the current consumption increases when the hysteresis occurs, as shown in FIG. This current consumption increases in proportion to the hysteresis width.

Accordingly, it is necessary to further reduce the power consumption of a hysteresis comparator incorporated in an integrated circuit or the like using a dry cell, a battery, or the like as a power supply. The present invention has been made in view of such conventional problems, and has as its object to provide a hysteresis comparator capable of reducing power consumption.

[0013]

Therefore, a hysteresis comparator according to the first aspect of the present invention divides a power supply voltage using a plurality of resistors to generate a reference voltage, and a short-circuit signal. A first short-circuiting means for short-circuiting the resistance on the power supply side when input, a second short-circuiting means for short-circuiting the resistance on the ground side when a short-circuit signal is input, and inputting a signal to be measured and a reference voltage. And a comparator for outputting a short-circuit signal to the first short-circuit means or the second short-circuit means in accordance with the comparison result between the signal level of the signal under measurement and the reference voltage.

According to this configuration, the power supply voltage is divided by the plurality of voltage dividing resistors of the reference voltage generating means, thereby generating the reference voltage. The signal under test is compared with this reference voltage by a comparator. Then, a short-circuit signal is output from the comparator to the first short-circuit means or the second short-circuit means according to the result of comparison between the signal level of the signal under measurement and the reference voltage. Therefore, the first short-circuit means and the second short-circuit means operate in reverse, and when a short-circuit signal is output to the first short-circuit means, the resistance on the power supply side is short-circuited by the first short-circuit means and the power supply is short-circuited. When the short-circuit signal is output to the second short-circuit means, the resistance on the ground side is short-circuited and the resistance value on the ground side is reduced, whereby the reference voltage changes and the hysteresis is reduced. Occurs. Also, on the power side,
Since only conduction / short-circuiting of the ground-side resistor is switched, a large current change due to the occurrence of hysteresis does not occur, and the current consumption does not change much even if the hysteresis width changes.

In the hysteresis comparator according to a second aspect of the present invention, the resistance on the power supply side short-circuited by the first short-circuit means and the resistance on the ground side short-circuited by the second short-circuit means have the same resistance value. have. According to such a configuration, even if the short-circuit resistance by the first short-circuit means and the second short-circuit means is switched, the resistances on the power supply side and the ground side have the same resistance value, regardless of the operation state. The current consumption is kept constant.

In the hysteresis comparator according to the third aspect of the present invention, the first short-circuit means and the second short-circuit means
It is a field effect transistor. According to such a configuration, switching between short-circuit and short-circuit release is quickly performed by the field-effect transistor.

[0017]

According to the hysteresis comparator according to the first aspect of the present invention, there is no need for a constant current source for generating hysteresis, and there is no large increase in current consumption due to the occurrence of hysteresis. Furthermore, even if the hysteresis width increases, the increase in current consumption can be almost ignored, and power consumption can be reduced. Therefore, it is extremely effective for use in an integrated circuit using a dry cell, a battery, or the like as a power source.

According to the hysteresis comparator according to the second aspect of the present invention, the current consumption can be kept constant regardless of the operation state. According to the hysteresis comparator of the third aspect, the switching speed is increased.

[0019]

FIG. 1 is a block diagram showing an embodiment of the present invention.
A description will be given based on FIG. FIG. 1 shows this embodiment. In FIG. 1 showing the present embodiment, a signal to be measured is supplied to a COMP (comparator) 3 via an input terminal IN.
And the output signal of COMP3 is output from the output terminal OUT.

Between the power supply and the ground, four resistors R31 and R
32, R33, and R34 are connected in series. Resistance R
31 and the resistor R34 have the same resistance value. COMP3
Of the resistor R32 as a reference voltage.
Voltage V _C of the connection point C is input and the resistor R33. The four resistors R31 to R34 constitute a reference voltage generation circuit as reference voltage generation means.

A resistor R3 is connected to both ends of the resistors R31 and R34.
1 and R34 are short-circuited, respectively,
Metal oxide silicon (S) field effect transistor 1
(Hereinafter referred to as "FET1"), n-channel MOS field effect transistor 2 (hereinafter referred to as "FET2")
Is connected. The gates of the FETs 1 and 2 are both CO
Connected to the output terminal of MP3, and the output signal of COMP3 is F
Output to the gate of ET1 or FET2. This output signal corresponds to the short circuit signal, and the FET
1 and 2 operate in opposite directions.

The FETs 1 and 2 correspond to first short-circuit means and second short-circuit means, respectively. Next, the operation will be described.
When the signal level of the measurement signal input via the input terminal IN is equal to or lower than the low threshold, the signal level of the output signal of COMP3 becomes Hi. This output signal is output from an output terminal O
While being output from the UT, it is also input to the FETs 1 and 2. As a result, the FET 1 is turned on (conducting), and the resistance R
31 is short-circuited.

On the other hand, the FET 2 has an OF
F (non-conduction). Therefore, the resistance between the power supply and ground is
R32 to R34, the reference voltage serving as the threshold value of COMP3 becomes the high threshold value VthH represented by the following equation, and is in a stable state. VthH = Vcc × (R33 + R34) / (R32 + R33 + R34) IccH = Vcc / (R32 + R33 + R34) where Vcc: power supply voltage IccH: current consumption at high threshold VthH R32 to R34: resistance Next, when the signal level of the signal under measurement changes above the high threshold value, the output signal of COMP3 becomes Lo level,
ET1 is turned off and FET2 is turned on. As a result, the resistor R34 is short-circuited, and the reference voltage of COMP3 becomes the low threshold value VthL expressed by the following equation, and enters a stable state.

VthL = Vcc × R33 / (R31 + R32 + R33) IccL = Vcc / (R31 + R32 + R33) where IccL: current consumption at low threshold VthL R31: resistance value of resistor R31 Since the resistors R31 and R34 have the same resistance value, the consumption currents IccH and IccL are equal, and are expressed by the following equation.

IccH = IccL = Vcc / (R31 + R32 + R) where R = R31 = R34 Also, the current consumption Ire without the hysteresis circuit
f, increase in consumption current Ih before and after occurrence of hysteresis
ys is represented by the following equation. Iref = Vcc / (R32 + R33 + R) (If there is no hysteresis, R31 or R34 is unnecessary.) Ihys = IccH-Iref = 0 (when COMP output is Hi) Ihys = IccH-Iref = 0 (COMP Therefore, the consumption current Icc in the reference voltage generation circuit is
It is kept constant as shown in FIG.

Next, the hysteresis width Vhys is expressed by the following equation. Vhys = VthH−VthL = (R / (R32 + R33 + R)) × Vcc Therefore, if the resistance values of the resistors R31 and R34 are increased, the hysteresis width Vhys is also increased. According to this configuration, the short-circuit FETs 1 and 2 that operate in opposite directions according to the output of the COMP 3 are connected to both ends of the power-supply-side resistor R31 and the ground-side resistor R34 of the reference voltage generating circuit to generate hysteresis. As a result, a current for generating hysteresis is not required, and there is no large change in resistance value due to the generation of hysteresis, so that power consumption can be reduced. Furthermore, even if the hysteresis width increases, the increase in current consumption can be ignored.

Therefore, the present invention is extremely effective for an integrated circuit that requires a reduction in current consumption in order to use a dry cell, a battery, or the like as a power supply. Further, by making the resistance values of the short-circuited resistor R31 and the resistor R34 the same, the current consumption Icc in the reference voltage generating circuit can be kept constant. In this embodiment, the FET is used as the short-circuit means of the voltage dividing resistor. However, the present invention is not limited to this. For example, a bipolar transistor or the like can be used.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating an embodiment of the present invention.

FIG. 2 is a timing chart showing the operation of FIG.

FIG. 3 is a circuit diagram of a conventional hysteresis comparator.

FIG. 4 is a timing chart showing the operation of FIG. 3;

FIG. 5 is a circuit diagram of another conventional hysteresis comparator.

FIG. 6 is a timing chart showing the operation of FIG.

[Explanation of symbols]

 COMP3 Comparator FET1 P-channel MOS field effect transistor FET2 N-channel MOS field effect transistor

Claims (3)

[Claims] 1. A reference voltage generating means for dividing a power supply voltage using a plurality of resistors to generate a reference voltage; a first short-circuit means for short-circuiting a resistor on a power supply side when a short-circuit signal is input; A second short-circuit means for short-circuiting a ground-side resistor when a short-circuit signal is input; a signal to be measured and a reference voltage being inputted; And a comparator that outputs the signal to the first short-circuit means or the second short-circuit means. 2. A power supply-side resistance short-circuited by said first short-circuit means and a ground-side resistance short-circuited by said second short-circuit means have the same resistance value. The hysteresis comparator according to claim 1. 3. The hysteresis comparator according to claim 1, wherein said first short-circuit means and said second short-circuit means are field effect transistors.