JP2870323B2 - Window comparator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a window comparator, and more particularly to a window comparator capable of setting a dead band width having a hysteresis characteristic.

[0002]

2. Description of the Related Art Conventionally, such a window comparator comprises a plurality of current mirror circuits, a dead band width control circuit, a voltage setting circuit, and a comparing section.

FIG. 2 is a circuit diagram of a window comparator showing an example of the related art. As shown in FIG. 2, the conventional window comparator includes a dead band control circuit 1.
A voltage setting circuit 3a, first and second current mirror circuits 8 and 9, comparison units 5 and 6 for comparing the output and input voltage VI of the voltage setting circuit 3a, respectively,
An AND circuit 7 is provided as a comparator output by calculating the logical product of the outputs of the comparison units 5 and 6, and the output of the AND circuit 7 is fed back to the dead band control circuit 1. In such a window comparator, the dead band width control circuit 1 includes a dead band width control power supply VZ.
, Resistors R1 and R2, switch transistor Q1,
And a buffer 2. The first current mirror circuit 8 includes PNP transistors Q3 and Q4 and resistors R8 and R4.
9, the second current mirror circuit 9 includes NPN transistors Q5 to Q7 and resistors R12 to R14. Further, the voltage setting circuit 3a includes resistors R7, R10, R1
1, is composed of a reference power supply V _R, and the power supply V _CC and the PNP transistor Q2, and outputs a connection point P3, P4.
The two outputs at these connection points P3, P4 are
, And is compared with the input voltage VI. The outputs of these comparators 5 and 6 are supplied to an AND circuit 7, and the output VO is fed back to the base of the switch transistor Q1.

First, when the input voltage VI is outside the dead zone, the output VO is low. Therefore, the switch transistor Q1 is turned off, and the dead band width control power supply V2 is applied to the base of the transistor Q2 forming the voltage setting circuit 3a. At this time, the voltage V _P3 at the connection point P3 is expressed by the following equation (1).

[0005]

Here, V _CC is a power supply voltage, and V _BE2 is a base-emitter voltage of the transistor Q2. Similarly, the voltage V _P4 connection point P4, is expressed by the following equation (2).

[0007]

Further, if the dead zone width V _D is obtained with the resistance R10 = R11, the following equation (3) is obtained.

[0009]

## EQU1 ## Thus, the window comparator in this case around the reference voltage V _R (2R10 / _R
7) It has a dead zone of × (V _CC -V _BE2 -V _Z ).

Next, when the input voltage VI changes to the inside of the dead zone, the output VO is High. Therefore, the switch transistor Q1 is turned on, and the transistor Q2
The base, the voltage of _{(V Z -V sat) × {} R2 / (R1 + R2)} + V sat ≒ V Z × {R2 / (R 1 + R2)} is applied. However, V _sat is the transistor Q1
And is ignored because it is sufficiently small.

Accordingly, when the dead zone width V _D at this time is calculated in the same manner as in the above equation (3), the following equation (4) is obtained.

[0013]

## EQU1 ## When this is compared with the dead zone width of the equation (3), as shown in the following equation (5),

[0015]

Only spread. This spread ΔV indicates a hysteresis characteristic.

In short, the conventional window comparator has a hysteresis characteristic.

[0018]

The above-described conventional window comparator has a resistor R10 due to the asymmetry of the first current mirror circuit and the second current mirror circuit.
And the magnitude of the current flowing through R11 is different. For this reason, the hysteresis at the upper end (voltage of P3) and the lower end (voltage of P4) of the dead zone are not equal.

For example, if the current flowing through the resistors R10 and R11 is calculated as k ₂ times and k ₃ times the current I ₁ flowing through the resistor R7, respectively, the hysteresis ΔV of the voltage at the connection point P3 is obtained.
_P3 is represented by the following equation (6).

[0020]

Similarly, the hysteresis ΔV _P4 of the voltage at the connection point _P4 is expressed by the following equation (7).

[0022]

As described above, the conventional window comparator has a disadvantage that the hysteresis is different between the upper end and the lower end of the dead zone.

An object of the present invention is to provide a window comparator capable of equalizing hysteresis at the upper end and the lower end of the dead zone.

[0025]

SUMMARY OF THE INVENTION A window comparator according to the present invention has a hysteresis of a dead band width with respect to an input voltage.
In controlling the characteristics, a switch transistor, first and second resistors, and a dead band control voltage source are provided .
Changing the voltage of the sensitive zone control voltage source to the first and second resistors.
Outputs the value divided by the resistance while the switch transistor
The dead band width control voltage source when the
, A third resistor having one end connected to the output terminal of the dead band width control circuit, a fourth resistor connected to the other end of the third resistor, and the fourth resistor. The other end of the resistor is connected between an inverting input and an operational amplifier supplied with a reference voltage to a non-inverting input, and is connected between the inverting input and the output of the operational amplifier and is equal to the fourth resistor and the third resistor, respectively. A voltage setting circuit including fifth and sixth resistors having resistance values;
Two comparison units for comparing a potential at a connection point between the third and fourth resistors and a connection point between the fifth and sixth resistors with an input voltage, respectively, as a reference; and a aND circuit for outputting a two-input, with the output of the aND circuit and the comparator output, and fed back to control the switching transistor before Symbol dead zone width control circuit.

[0026]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of a window comparator showing one embodiment of the present invention. As shown in FIG. 1, in the present embodiment, the dead band width control circuit 1, the comparators 5, 6, and the AND circuit 7 are the same as those in the conventional example of FIG. , 9 are omitted, and the voltage setting circuit 1 is improved. The voltage setting circuit 3 includes a resistor R3 connected to the output of the buffer 2 of the dead zone control circuit 1, a resistor R4 connected to the other end of the resistor R3, and a resistor R4 connected to the inverting input of the other end of the resistor R4. operational amplifier is supplied with the reference voltage V _R to the inverting input 4
And resistors R5 and R6 connected between the inverting input and the output and having resistances equal to the resistors R4 and R3, respectively.

The reference voltage V _R to the non-inverting input of the operational amplifier 4 is connected to the inverting input, the resistors R1, R2 and the switch transistor Q1 and the dead zone width control voltage V _Z
And the output of the dead band width control circuit 1 composed of the buffer 2 are connected via resistors R3 and R4. On the other hand, the inverting input of the operational amplifier 4 further includes resistors R5 and R6.
The output terminal of the operational amplifier 4 is connected via the terminal. As described above, these resistors R3 to R6 are connected to R4, R5, and R5.
3 and R6 are set to have equal resistance values.

As described above, the connection points P1 and P
And each voltage V _P1 of 2 and V _P2 is transmitted to one of each of the input terminals of the comparator unit 5 and 6, are compared to the common input signal VI supplied to the other input terminal. The outputs of these comparators 5 and 6 are input to an AND circuit 7, and the output VO becomes a comparator output and a dead band width control circuit 1
To the base of the switch transistor Q1.

In such a window comparator,
First, when the input VI is outside the dead zone, the output VO is Lo.
w. Therefore, the switch transistor Q1 is turned off, and the dead band width control voltage V2 is supplied to the buffer 2. At this time, the voltage V _P1 at the connection point P1 is expressed by the following equation (8).

[0030]

Further, the voltage V _P2 at the connection point P2 is expressed by the following equation (9). However, R3 = R6, R4 = R5
And

[0032]

When the dead zone width V _D is obtained from these voltages, the following equation (10) is obtained.

[0034]

[0035] Thus the window comparator in this case around the reference voltage _{V R {2R4 / (R3 +} R4}
It will have a dead zone of (V _R -V _Z).

Next, when the input VI changes to the inside of the dead zone, the output VO is High, and the switch transistor Q1 turns on. Therefore, (V _Z -V _sat ) × {R2 / (R1 + R2)} + V _sat {R2 / (R1 + R2)} × V _Z is applied to the buffer 2. Therefore, when the dead zone width V _D at this time is calculated, the following equation (11) is obtained.

[0037]

## EQU4 ## Comparing the dead zone width expressed by the equation (11) with the dead zone width of the equation (10), the following (1) is obtained.
2) Voltage ΔV expressed by equation

[0039]

Only spreads. That is, it has a hysteresis characteristic.

The hysteresis at the upper end (voltage of P1) and the lower end (voltage of P2) of the dead zone are expressed by the following equations (13).

[0042]

And becomes equal.

[0044]

As described above, the window comparator according to the present invention can ignore the current flowing into the inverting input of the operational amplifier by applying the reference voltage through the operational amplifier, and thus can flow through the resistors R4 and R5. There is an effect that the current values can be made equal and the hysteresis at the upper end and the lower end of the dead zone can be made exactly equal.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a window comparator showing one embodiment of the present invention.

FIG. 2 is a circuit diagram of a window comparator showing an example of the related art.

[Explanation of symbols]

1 dead zone width control circuit 2 buffer 3 voltage setting circuit 4 op 5,6 comparison unit 7 the AND circuit R1~R6 resistor Q1 switching transistor V _Z dead zone width control voltage V _R the reference power source VI Input voltage VO Output voltage

Claims (2)

(57) [Claims] 1. A hysteresis of a dead band width with respect to an input voltage.
A switch transistor, a first resistor, a second resistor, and a dead band control voltage source for controlling the switching characteristics.
Changing the voltage of the sensitive zone control voltage source to the first and second resistors.
Outputs the value divided by the resistance while the switch transistor
The dead band width control voltage source when the
, A third resistor having one end connected to the output terminal of the dead band width control circuit, a fourth resistor connected to the other end of the third resistor, and the fourth resistor. The other end of the resistor is connected between an inverting input and an operational amplifier supplied with a reference voltage to a non-inverting input, and is connected between the inverting input and the output of the operational amplifier and is equal to the fourth resistor and the third resistor, respectively. A voltage setting circuit including fifth and sixth resistors having resistance values;
Two comparison units for comparing a potential at a connection point between the third and fourth resistors and a connection point between the fifth and sixth resistors with an input voltage, respectively, as a reference; and a aND circuit for outputting a two-input, the aND output of the circuit with a comparator output, window comparator, characterized in that the feedback to control the switching transistor before Symbol dead zone width control circuit. 2. The window comparator according to claim 1, wherein said voltage setting circuit uses one reference voltage source.