JP2002300011A - Voltage comparator with hysteresis - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage comparator with hysteresis that can select a threshold value with a simple circuit. SOLUTION: The voltage comparator with hysteresis is provided with a selector that selects a threshold value by a logic input signal and a plurality of N-MOS transistors (TRs) to change the threshold value so as to select one threshold value among a plurality of the threshold values with a comparatively simple circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic circuit capable of selecting a threshold voltage of a voltage comparator circuit with hysteresis by a logic signal.

[0002]

2. Description of the Related Art As a conventional voltage comparator with hysteresis, a circuit as shown in FIG. 6 is known. That is, the resistor 104 for dividing the input voltage Vin into a voltage,
A reference point of the reference voltage source 101 is connected to a non-inverting input terminal which is one input terminal of the voltage comparator 102, and a connection point between the resistors 104 and 105 is connected to an inverting input terminal of the voltage comparator 102. It is connected. Voltage comparator 10
2 is connected to the gate of the N-MOS transistor 108, the source of the N-MOS transistor 108 is grounded, and the drain is connected to the resistors 105 and 106 for dividing the input voltage Vin. Connected to the connection point.

When the input voltage Vin is low, the voltage comparator 1
The terminal Vout, which is the output of 02, is in the “High” state, and the N-MOS transistor 108 is in a conductive state.
Therefore, the voltage VA at the terminal A, which is the connection point between the resistors 104 and 105, is determined by setting the resistance values of the resistors 104 and 105 to R10
4, R105

[0004]

(Equation 1)

[0005] The input voltage Vin rises and the terminal A
Is higher than the output voltage Vref of the reference voltage source 101, the terminal Vout, which is the output of the reference voltage source 102, is in the “Low” state. Therefore, the terminal Vout is set to “Hig
input voltage Vin that changes from the “h” state to the “Low” state
Is given by VA = Vref in equation (1).

[0006]

(Equation 2)

[0007]

The input voltage Vin obtained from the equation (2) is the upper threshold voltage.

When the input voltage Vin is high, the voltage comparator 1
The terminal Vout, which is the output of No. 02, is in the “Low” state, and the N-MOS transistor 108 is off. Accordingly, the voltage VA at the terminal A, which is the connection point between the resistors 104 and 105, is given by the following equation:

[0010]

(Equation 3)

## EQU1 ## The input voltage Vin falls and the terminal A
Is lower than the output voltage Vref of the reference voltage source 101, the terminal Vout, which is the output of the reference voltage source 102, is in the “High” state. Therefore, the terminal Vout becomes “Lo”
input voltage Vi that changes from the “w” state to the “High” state
n is given by VA = Vref in equation (3).

[0012]

(Equation 4)

## EQU1 ## Input voltage V obtained from equation (4)
in is the lower threshold voltage.

FIG. 7 shows the above operation with the input voltage Vin on the horizontal axis.
And the vertical axis is shown as the output Vout.
The difference between the upper threshold voltage and the lower threshold voltage is the hysteresis width.

[0015]

In the case of the conventional voltage comparator with hysteresis shown in FIG.
Since the upper threshold value and the lower threshold value are determined by the resistance values 5 and 106, the threshold values cannot be selected because both threshold values are fixed values. In order to select the threshold value, it is necessary to prepare a plurality of voltage comparators 102 shown in FIG. 6 and the circuit scale is increased, which is not a good idea.

[0016]

In the present invention, it is relatively simple to prepare a selector for selecting a threshold value by a logic input signal and a plurality of N-MOS transistors for changing the threshold value. One of the threshold values can be selected by a simple circuit.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to solve the above problems, in the present invention, a selector for selecting a threshold by a logic input signal and an N-MOS for changing the threshold are provided.
It has a transistor.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a voltage comparator circuit with variable hysteresis according to a first embodiment of the present invention. That is, the input voltage Vi
resistors 104, 105, 106 for dividing n
107, the connection point between the resistors 104 and 105 is connected to the inverting input terminal of the voltage comparator 102, and the reference voltage source 101 is connected to one non-inverting input terminal of the voltage comparator 102. Have been. The terminal Vout which is the output of the voltage comparator 102 is connected to the AND circuit 100 and the OR circuit 1
03 is input to the selector 110. The selector 110 supplies the logic signal “H” from the terminal SELECT.
An "high" state or a "Low" state is input.An output of the AND circuit 100, which is one output of the selector 110, is connected to the gate of the N-MOS transistor 108, and the source of the N-MOS transistor 108 is grounded. The drain is connected to a connection point between the resistors 105 and 106 for dividing the input voltage Vin.
The output of the OR circuit 103, which is another output of the selector 110, is connected to the gate of the N-MOS transistor 109, the source of the N-MOS transistor 109 is grounded, and the drain is for dividing the input voltage Vin. Are connected to the connection point between the resistors 106 and 107.

When the terminal SELECT is in the “Low” state, the output of the AND circuit 10
0 is always in the “Low” state, so that the N-MOS
Transistor 108 is always off. On the other hand, the output state of the voltage comparator 102 is output as it is to the output of the OR circuit 103, which is another output of the selector 110. When the input voltage Vin is low while the terminal SELECT is in the “Low” state, the terminal Vout which is the output of the voltage comparator 102 is in the “High” state, and the output of the OR circuit 103 which is one output of the selector 110 is also in the “High” state. Therefore, the N-MOS transistor 109 is turned on. Therefore, assuming that the resistance values of the resistors 104, 105, and 106 are R104, R105, and R106, respectively, the voltage VA at the terminal A is

[0021]

(Equation 5)

## EQU1 ##

The input voltage Vin rises and the voltage V at the terminal A
When A exceeds the output voltage Vref of the reference voltage source 101, the terminal Vout which is the output of the reference voltage source 102 is "Low".
State. Accordingly, the input voltage Vin at which the terminal Vout changes from the “High” state to the “Low” state is calculated by setting VA = Vref in equation (5).

[0024]

(Equation 6)

## EQU1 ##

The input voltage Vin obtained from the equation (6) is the upper threshold voltage when the terminal SELECT is in the “Low” state.

If the input voltage Vin is high while the terminal SELECT is in the “Low” state, the terminal Vout, which is the output of the voltage comparator 102, is in the “Low” state, and the selector 110
The output of the OR circuit 103 which is one of the outputs is also “Low”.
Therefore, the N-MOS transistor 109 is turned off. Therefore, the voltage VA at the terminal A, which is the connection point between the resistors 104 and 105, is determined by changing the resistance values of the resistors 104, 105, 106, and 107 to R104, R105, and R10, respectively.
6, R107

[0028]

Equation 7

## EQU1 ##

The input voltage Vin drops and the voltage V at the terminal A
When A becomes lower than the output voltage Vref of the reference voltage source 101, the terminal Vout which is the output of the reference voltage source 102 becomes “Hig”.
Therefore, the input voltage Vin at which the terminal Vout changes from the “Low” state to the “High” state is set by VA = Vref in the equation (7).

[0031]

(Equation 8)

## EQU1 ##

The input voltage Vin obtained from the equation (8) is the lower threshold voltage when the terminal SELECT is in the “Low” state.

When the terminal SELECT is in the “High” state, the OR circuit 103 which is one output of the selector 110
Is always in a “High” state, so that the N-MOS
The transistor 109 is always on. On the other hand, the output state of the voltage comparator 102 is output as it is to the output of the AND circuit 100, which is another output of the selector 110. When the input voltage Vin is low while the terminal SELECT is in the “High” state, the terminal Vout which is the output of the voltage comparator 102 is in the “High” state, and the output of the AND circuit 100 which is one output of the selector 110 is also in the “High” state. Therefore, the N-MOS transistor 108 is turned on. Therefore, assuming that the resistance values of the resistors 104 and 105 are R104 and R105, respectively, the voltage VA at the terminal A is

[0035]

[Equation 9]

## EQU1 ##

The input voltage Vin rises and the voltage V at the terminal A
When A exceeds the output voltage Vref of the reference voltage source 101, the terminal Vout which is the output of the reference voltage source 102 is "Low".
State. Therefore, the input voltage Vin at which the terminal Vout changes from the “High” state to the “Low” state is determined by VA = Vref in equation (9).

[0038]

(Equation 10)

## EQU1 ##

The input voltage Vin obtained from the equation (10) is the upper threshold voltage when the terminal SELECT is in the “High” state.

If the input voltage Vin is high while the terminal SELECT is in the “High” state, the terminal Vout, which is the output of the voltage comparator 102, is in the “Low” state and the selector 11
The output of the AND circuit 100 which is one output of “0” is also “Lo”.
As a result, the N-MOS transistor 108 is turned off, and the voltage VA at the terminal A, which is the connection point between the resistors 104 and 105, becomes
6 are R104, R105, and R106, respectively.

[0042]

[Equation 11]

Is as follows.

The input voltage Vin drops and the voltage V at the terminal A
When A becomes lower than the output voltage Vref of the reference voltage source 101, the terminal Vout which is the output of the reference voltage source 102 becomes “Hig”.
Therefore, the input voltage Vin at which the terminal Vout changes from the “Low” state to the “High” state is (1).
By setting VA = Vref in equation (1),

[0045]

(Equation 12)

Is as follows.

The input voltage Vin obtained from the equation (12) is the upper threshold voltage when the terminal SELECT is in the “Low” state.

The above is summarized in Table 1 below.

[0049]

[Table 1]

FIG. 2 shows the above operation with the input voltage Vin on the horizontal axis.
And the vertical axis is shown as the output Vout.

FIG. 3 shows a voltage comparator circuit with variable hysteresis according to a second embodiment of the present invention. The second embodiment shown in FIG. 3 is different from the first embodiment shown in FIG. 1 in that the selector 110 includes an AND circuit 100, an inverter circuit 111, and a NOR circuit 112.

In FIG. 3, when the terminal SELECT is in the "Low" state, the output of the AND circuit 100 which is one output of the selector 110 is always "Low", and the N-MOS transistor 108 is always in the non-conductive state. On the other hand, the output state of the voltage comparator 102 is output as it is to the output of the NOR circuit 103 which is another output of the selector 110.
The operation when the terminal SELECT is in the “Low” state is the same as in the first embodiment. That is, the upper threshold is (6), and the lower threshold is (8).

When the terminal SELECT is in the “High” state, the NOR circuit 1 which is one output of the selector 110
12 is always in the "Low" state, so that the N-MO
S transistor 109 is always off. On the other hand, the output state of the voltage comparator 102 is output as it is to the output of the AND circuit 100, which is another output of the selector 110. When the terminal SELECT is “High”, the upper threshold value is obtained by setting the resistance values of the resistors 104 and 105 to R10
4, R105

[0054]

(Equation 13)

Is as follows.

When the terminal SELECT is at “High”, the lower threshold value is the resistance of the resistors 104, 105, 106, 1
07 resistance values R104, R105, and R10, respectively.
6, assuming R107

[0057]

(Equation 14)

Is as follows.

The above is summarized in Table 2 below.

[0060]

[Table 2]

FIG. 4 shows the above operation with the input voltage Vin on the horizontal axis.
And the vertical axis is shown as the output Vout.

FIG. 5 shows a voltage comparator circuit with variable hysteresis according to a third embodiment of the present invention. A plurality of control terminals are connected to the selector 110 in order to arbitrarily add a resistor and an N-MOS transistor for dividing the input voltage Vin and to select one threshold from a plurality of thresholds. Obviously, the upper threshold value and the lower threshold value can be obtained in the same manner as in the first and second embodiments.

[0063]

According to the voltage comparator circuit with variable hysteresis of the present invention, it is possible to select an arbitrary threshold value combination from a plurality of threshold value combinations without increasing the circuit scale.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a voltage comparator circuit with variable hysteresis according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of the operation of the circuit of the first embodiment.

FIG. 3 is a circuit diagram of a voltage comparator circuit with variable hysteresis according to a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of the operation of the circuit of the second embodiment.

FIG. 5 is a circuit diagram of a voltage comparator circuit with variable hysteresis according to a third embodiment of the present invention.

FIG. 6 is a circuit diagram of a conventional voltage comparator circuit with hysteresis.

FIG. 7 is an operation explanatory diagram of a conventional voltage comparator circuit with hysteresis.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 AND circuit 101 reference voltage source 102 voltage comparator 103 OR circuit 104 to 107, 113 resistance 108, 109, 114 N-MOS transistor 110 selector 111 inverter circuit 112 NOR circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G035 AA19 AB01 AC01 AC18 AC19 AD03 AD11 AD23 AD27 AD47 AD56 5H410 BB04 CC02 DD02 EA11 EA12 EB01 FF03 FF25 5J039 DA12 DB09 DB20 KK10 MM16

Claims (1)

[Claims] 1. A voltage comparator with hysteresis wherein a combination of an upper threshold voltage and a lower threshold voltage as a pair of threshold voltages of a voltage comparator circuit with hysteresis can be selected by a logic input signal. circuit