KR980012898A - Comparator with bi-directional hysteresis - Google Patents

Abstract

The present invention discloses a comparator with bidirectional hysteresis. The circuit comprises: comparison means having a negative input terminal to which a reference voltage is applied; first and second resistors connected in series between an input voltage and a positive input terminal of the comparison means: A first current source flowing between the first and second electrodes; A second current source connected to a common point between the second resistor and the positive input terminal of the comparison means; And switching means controlled by the output voltage of the comparing means and connected between the second current source and the ground voltage. Therefore, it has a simple circuit configuration using one comparator, and it is also easy to change the hysteresis voltage.

Description

Comparator with bi-directional hysteresis

Figure 1 is a block diagram of a comparator with a conventional bidirectional hysteresis;

Fig. 2 is an operational waveform diagram of the block diagram shown in Fig. 1,

Figure 3 is a circuit diagram of a comparator with bidirectional hysteresis of the present invention;

4 is an operation waveform diagram of the block diagram shown in Fig.

[Object of the invention]

[TECHNICAL FIELD OF THE INVENTION AND RELATED ART OF THE SAME]

The present invention relates to a comparator, and more particularly to a comparator having bi-directional hysteresis.

A comparator with conventional hysteresis has a hysteresis at one-way switching points. That is, it was a comparator having a hysteresis at the point of transition from the "high" level to the "low" level or the "low" level to the "high" level. The output of the conventional comparator has the same input and period but different duty. When this output is used as an input to another block, if only one directional trigger (positive edge trigger or negative edge trigger) is used in that other block, there is no redemption even if the duty is not 50%. Using one-way triggers; This is because the data is used only for the periodicity. However, if you have to use both bidirectional edge triggers, then the duty is very important.

So, in order to transfer the duty of the input to the output as it is, the hysteresis of the same size must be made in the bidirectional trigger.

FIG. 1 is a block diagram of a comparator with conventional bi-directional hysteresis, comprising comparators 10 and 12, and NAND gates 14.16. The comparator 10 is a high-level comparator, and the comparator 12 is a low-level comparator. The NAND gates 14 and 16 are latches for latching and outputting data.

2 is an operational waveform diagram of the comparator shown in Fig. 1. When the input signal Inn is higher than the high level voltage Vhi, the switching occurs at the point a and the output signal of the comparator 10 is at a high level . This value should be switched by the comparator 10 even at the point ⓐ, but the output Vo is maintained at the high level by the latches 14 and 16.

When the input signal Vin is lower than the lower level voltage Vlo, the switching occurs at the point (b), and the output signal of the comparator 12 becomes the "low" level. This value should be switched by the comparator 12 at the point of d ', but the output Vo is kept at the "low" level by the latches 14, 16. That is, the high-level comparator 10 switches only at the points ⓐ and ⓒ. At ⓐ ', ⓒ' point, switching does not occur and the previous state is maintained. Then, the low-level comparator 12 performs the switching only at the points b and d, and the switching state does not occur at the points 'b' and 'd'.

Such a comparator of the second embodiment requires two comparators and has a disadvantage that the hysteresis can not be easily varied.

[Technical Problem]

An object of the present invention is to provide a comparator in which the circuit configuration is simple and the hysteresis is easily variable.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a comparator comprising: a comparator having a negative input terminal to which a reference voltage is applied; First and second resistors connected in series between an input voltage and a positive input terminal of the comparing means; A first current source flowing between a power supply voltage and a common point of the first and second resistors; A second current source connected to a common point between the second resistor and the positive input terminal of the comparison means; And switching means controlled by the output voltage of the comparing means and connected between the second current source and the ground voltage.

Further, the present invention provides a semiconductor device comprising comparison means having a negative input terminal to which a reference voltage is applied; And a comparator for comparing a voltage obtained by subtracting the predetermined first voltage level from the input voltage to a positive input terminal of the comparing means when the input voltage rises to a level higher than the reference voltage, And bidirectional hysteresis input means for supplying a voltage obtained by subtracting a predetermined second voltage level from the input voltage to a positive input terminal of the comparison means when the input voltage falls from a level higher than the reference voltage to a low level .

[Structure of the Invention]

The comparator of the present invention will now be described with reference to the accompanying drawings.

3 is a circuit diagram of a comparator having bidirectional hysteresis according to the present invention. The comparator 20 includes a comparator 20 having a negative input terminal to which a reference voltage Va is applied, a comparator 20 connected in series between the input voltage Vin and the positive input terminal of the comparator 20, The constant current source 11 flowing between the connected resistors R1 and R2 and the common point of the power supply voltage Vcc and the resistors R1 and R2 is connected to the common point of the resistor R2 and the positive input terminal of the comparator 20 A constant current source I2 and a switch 22 controlled by the output Vo of the comparator 20 and connected between the constant current source 12 and the ground voltage.

Fig. 4 is an operational waveform diagram of the comparator shown in Fig. 3, in which the switch 22 is turned off when the input voltage Vin goes from the "low" level (Vin Va) to the "high" level (Vin> Vb). Therefore, all the current of the current source Il flows through the resistor Rl. At this time. The voltage Vb applied to the positive input terminal of the comparator 20 becomes Va + I1 * RI. Therefore,

The reference voltage is shifted from Va to the voltage (Vb = Va + I1 * Rl), resulting in a hysteresis of Il * Rl. Then, the output voltage Vo of the comparator 20 becomes the "high" level and the switch 22 is turned on.

Assuming that Il > 12, R2 > Rl, a current of the current I2 flows through the resistor R2 and a current of Il-12 flows through the resistor R1. Therefore, the voltage (Vc = Va + Rl * (I1-I2) -R21 * 2) applied to the node A becomes smaller than the voltage Va. That is, the resistors R1 and R2 and the constant current sources I1 and 12 are designed such that the voltage Vc across the node A is smaller than the voltage Va. Therefore, the switching point when the input voltage Vin advances from the high level to the low level occurs at a value smaller than the voltage Va, and the hysteresis of the value R2 * I2-Rl (Il-f2) .

However, in order to produce an output waveform having a duty of 50%, bidirectional hysteresis, that is, the hysteresis of the upper side and the lower side must be the same. That is, the following equation (1) must be satisfied.

II * RI = (I2 * R2) -R1 (II-12)

= 12 * R2-I1 * R1 + I2 * R2

2Il * Rl = (R1 + R2) * 12 (1)

Assume the value of a resistor or a constant current source or a proportional relationship to determine each value. Assuming that Il = 2I2, equation (1) is expressed by equation (2) below.

2I1 * R1 = (R1 + R2) * 0.5I1

2 R1 = 0.5 (R1 + R2)

R2 = 3R1 (2)

That is, when the relationship of Il = 2I2 and R2 = 3Rl is satisfied, an output voltage Vo of 70% duty occurs when the input voltage Vin has a duty of 50%, and the magnitude of the hysteresis is as follows.

The upper hysteresis is expressed by Il * Rl, and the lower hysteresis is expressed by the following equation (3).

12 * R2- (II-I2) * R1 = 0.5I1 * R2-0.5I1 * R1

= 0.5I1 * (R2-Rl) (3)

[Effects of the Invention]

Therefore, the comparator of the present invention can adjust the hysteresis voltage to be large or small by adjusting the values of the constant current sources Il and I2 and the resistors R1 and R2.

The comparator with bidirectional hysteresis of the present invention has a simple circuit configuration using one comparator.

It is also easy to vary the hysteresis voltage.

Claims (6)

Comparison means having a negative input terminal to which a reference voltage is applied; First and second resistors connected in series between an input voltage and a positive input terminal of the comparing means; A first current source flowing between a power supply voltage and a common point of the first and second resistors; A second current source connected in common to said second resistor and said positive input terminal of said comparison means; And switching means controlled by an output voltage of the comparing means and connected between a second current source and a ground voltage. The comparator of claim 1, wherein the current value of the first current source is twice the current value of the second current source. 2. The comparator of claim 1, wherein the threshold value of the second resistor is three times the resistance value of the first resistor. The comparator of claim 1, wherein a ratio of the first resistor and the second resistor is obtained by a ratio of the first current source and the second current source. Comparison means having a negative input terminal to which a reference voltage is applied; And a comparator for comparing a voltage obtained by subtracting a predetermined first voltage level from the input voltage to a positive input terminal of the comparing means when the input voltage rises from a level lower than the reference voltage to a high level, And bidirectional hysteresis input means for supplying a voltage obtained by subtracting a predetermined second voltage level from the input voltage to a positive input terminal of the comparison means when the input voltage falls from a level higher than the reference voltage to a low level A comparator The method as claimed in claim 5, wherein the first voltage level is equal to the second voltage level and the output duty ratio of the comparison means is set to 50% ※ Note: It is disclosed by the contents of the first application.