KR20070016056A - Voltage comparator having hysteresis characteristics - Google Patents

Abstract

The present invention relates to a voltage comparator having hysteresis characteristics, and by adding a reference voltage changer composed of a small number of elements inside a circuit, it is possible to design a voltage comparator which is stable against input noise, and also has a magnitude of hysteresis voltage. Can be set accurately, and the magnitude of the hysteresis voltage can be easily changed by changing the resistance value.

According to an embodiment of the present invention, there is provided a voltage comparator having a hysteresis characteristic, including: a comparator for comparing a reference voltage and an input voltage with each other and outputting a high level or low level signal; And a reference voltage changer configured to change the reference voltage when a low level output signal is generated from the comparator.

Voltage comparator, reference voltage change section, reference voltage, hysteresis, noise

Description

Voltage comparison with hysteresis characteristics {VOLTAGE COMPARATOR HAVING HYSTERESIS CHARACTERISTICS}

1 is a circuit diagram of a voltage comparison circuit according to the prior art

2 is a view showing an operation process and output signal according to the voltage comparison circuit according to the prior art

3 is a view showing an output signal according to the input noise into the voltage comparison circuit according to the prior art

4 is a circuit diagram of a voltage comparison unit according to the present invention;

5 is a view showing the hysteresis characteristics of the voltage comparison in accordance with the present invention

6 is a view showing an output signal according to the input noise into the voltage comparison circuit according to the present invention

<Description of Major Symbols in Drawing>

400: comparison unit 401: switching unit

401a: first transistor 401b: second transistor

401c: third transistor 401d: fourth transistor

402: signal output section 402a: fifth transistor

402b: sixth transistor 405: voltage drop means

405a: seventh transistor 405b: eighth transistor

408: bias current portion 409: second resistor

410: third resistor 411: reference voltage changing unit

412: ninth transistor 413: first resistor

414: tenth transistor E: input noise

Vref: reference voltage Vref´: changed reference voltage

The present invention relates to a voltage comparator having hysteresis characteristics, and by adding a reference voltage changer composed of a small number of elements inside a circuit, it is possible to design a voltage comparator which is stable against input noise, and also has a magnitude of hysteresis voltage. It can be set accurately, and the voltage comparator having hysteresis characteristics that can easily change the magnitude of the hysteresis voltage through the change of the resistance value.

In general, a voltage comparator compares an input voltage with a reference voltage, amplifies the difference, and outputs a high or low output. In the conventional voltage comparator, there is no noise compensation function at the output, so a separate analog or digital compensation circuit is added.

At this time, a circuit added to the voltage comparator in order to solve the noise problem includes a Schmitt Trigger circuit having hysteresis characteristics. And in determining a negative threshold voltage (Vth-), it is disadvantageous in that it is sensitive to process changes.

Therefore, these days, voltage comparison is designed to have hysteresis characteristics in itself.

A voltage comparator having hysteresis characteristics is used to compare input signals by comparing an input voltage with a reference voltage and then outputting a high or low signal when the input voltage is higher than the reference voltage.

Here, the hysteresis characteristic means that there are two points at which the output changes, that is, the upper reference voltage and the lower reference voltage.

In order to implement a voltage comparator that is resistant to noise, it must be designed to have hysteresis characteristics. Therefore, if the hysteresis characteristic varies depending on the process, an error occurs in the voltage comparator itself, which causes problems in the reliability of the entire semiconductor. do.

1 is a circuit diagram of a voltage comparison circuit 100 according to the prior art. As shown in FIG. 1, the voltage comparison circuit 100 according to the prior art is driven by the input voltage Vin. The voltage drop is connected to the transistors 101 and 102, the third and fourth transistors 103 and 104 driven by the reference voltage Vref, the second and third transistors 102 and 103, and the ground terminal. A voltage drop means 105, a fifth transistor 106 connected to the second transistor 102 and a ground terminal and driven by a voltage generated by the voltage drop means 105, and the fifth transistor ( 106 and a sixth transistor connected to a ground terminal and driven by a power supply voltage; 107 and the first, fourth, fifth, and sixth transistors 101, 104, 106, and 107 and the second and third transistors 102. It is connected to the common terminal of the 103, consisting of a bias current unit 108 for maintaining a constant amount of current There is.

The first to fourth transistors 101 to 104 are PNP transistors, and the fifth and sixth transistors 106 and 107 are NPN transistors.

The voltage drop means 105 is composed of seventh and eighth transistors 105a and 105b in a current mirror relationship, and the seventh and eighth transistors 105a and 105b are NPN transistors.

When the voltage comparison circuit 100 according to the related art having the above-described configuration outputs a signal having a high or low level by comparing the input voltage Vin and the reference voltage Vref, FIG. If you look at this in detail as follows.

2 is a view showing the operation of the voltage comparison circuit according to the prior art and the resulting output signal, (a) shows the input voltage (Vin) and the reference voltage over time to the voltage comparison circuit, (b Denotes the output signal Vout over time to the voltage comparison unit.

First, when the input voltage Vin is smaller than the reference voltage Vref, that is, in the A section, the second transistor 102 is turned on and the third transistor 103 is turned off due to the characteristics of the PNP transistor. The bias current I _1a of the comparison circuit 100 flows to I _2a , whereby a voltage drop occurs in the voltage drop means 105 so that a voltage having a predetermined magnitude is applied to the emitter of the fifth transistor 106. Is approved. In this case, since the magnitude of the voltage is greater than the magnitude of the threshold voltage of the fifth transistor 106, the fifth transistor 106 is turned on.

Accordingly, the collector-emitter voltage of the fifth transistor 106 is applied to the emitter of the sixth transistor 107, and the voltage is typically about 0.1V so that the threshold voltage of the sixth transistor 107 is applied. Since it does not reach the size, the sixth transistor 107 is turned off.

Accordingly, the power supply voltage VDD is applied to the output terminal of the voltage non-converting circuit 100, and as a result, a signal having a 'high' level is output as shown in (b).

On the other hand, when the input voltage Vin is greater than the reference voltage Vref, that is, in the period B, the second transistor 102 is turned off and the third transistor 103 is turned on due to the characteristics of the PNP transistor. The bias current I _1a of the voltage comparator 100 flows to I _3a , so that the voltage drop does not occur in the voltage drop means 105 so that the fifth transistor 106 can be turned on. The fifth transistor 106 is turned off because no emitter voltage is applied.

Therefore, the power supply voltage VDD of the voltage comparison circuit 100 is applied to the emitter of the sixth transistor 107. Accordingly, as shown in (b), the sixth transistor 107 is applied to the emitter of the sixth transistor 107. When turned on, a low level signal is output to the output terminal of the voltage comparison circuit 100.

3 is a view showing an output signal according to input noise into a voltage comparison circuit according to the prior art, (a) is when the noise is generated in a section where the input voltage (Vin) is greater than the reference voltage (Vref) The input voltage Vin and the reference voltage Vref are shown, and (b) shows the output signal when the noise is generated.

As shown in FIG. 3, in the conventional voltage comparison path as described above, noise C may be generated at the input voltage Vin in a section in which the input voltage Vin is greater than the reference voltage Vref. Although the output to the voltage comparator is a stable voltage comparator only when the low level is maintained, the conventional voltage comparator outputs a high level signal in response to the noise (C). There was a problem that the input noise was unstable.

Accordingly, the present invention has been made to solve the above problems, and by adding a reference voltage changer composed of a small number of elements inside the circuit, it is possible not only to design a stable voltage comparator with respect to input noise, but also the magnitude of the hysteresis voltage. It is possible to accurately set and to provide a voltage comparator having hysteresis characteristics that can easily change the magnitude of the hysteresis voltage through the change of the resistance value.

According to an embodiment of the present invention, there is provided a voltage comparator having a hysteresis characteristic, including: a comparator for comparing a reference voltage and an input voltage to output a high level or low level signal; And a reference voltage changer configured to change the reference voltage when a low level output signal is generated from the comparator.

Here, the comparison unit, the switching unit driven by the input voltage and the reference voltage; Voltage drop means connected to the switching unit and the ground terminal to generate a voltage drop; A signal output unit connected to the voltage drop unit to output a high level or low level signal through an output terminal; And a bias current unit connected to the switching unit and the signal output unit to maintain a constant current amount.

In this case, the switching unit, the first and second transistors driven by the input voltage; And third and fourth transistors driven at the reference voltage.

The signal output unit may further include: a fifth transistor connected to the second transistor and the ground terminal and driven by a voltage generated by the voltage drop means; And a sixth transistor connected to the fifth transistor and the ground terminal and driven by a power supply voltage.

The first to fourth transistors of the switching unit are PNP transistors, and the fifth and sixth transistors of the signal output unit are NPN transistors.

The voltage drop means is composed of seventh and eighth transistors in a current mirror relationship.

In this case, the seventh and eighth transistors are characterized by being composed of NPN transistors.

The reference voltage changing unit may include a ninth transistor connected to the third transistor and the fourth transistor; A first resistor connected in series with the ninth transistor; And a tenth transistor connected to the first resistor and the ground terminal and connected to the common terminal of the fifth and sixth transistors.

On the other hand, when the input voltage is less than the reference voltage, the second and fifth transistors are turned on and the third and six transistors are turned off, and outputs a high level signal through an output terminal. It is done.

In this case, the tenth transistor of the reference voltage changing unit is turned off.

On the other hand, when the input voltage is greater than the reference voltage, the third and sixth transistors are turned on and the second and fifth transistors are turned off to output a low level signal through an output terminal. do.

In this case, the ninth and tenth transistors of the reference voltage change unit are turned on.

The first resistor of the reference voltage changing unit may be a variable resistor capable of changing a resistance value.

In addition, in order to protect the sixth transistor of the signal output unit, a second resistor is connected between the collector of the fifth transistor and the base of the tenth transistor, and between the collector of the fifth transistor and the base of the sixth transistor. The third resistor is connected.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 4 is a circuit diagram of a voltage comparator according to the present invention. As shown in FIG. And a reference voltage changing unit 411 for changing the reference voltage Vref when a low level output signal is generated from the comparing unit 400.

Here, the comparison unit 400 is connected to the switching unit 401 driven by the input voltage Vin and the reference voltage Vref, and the voltage connected to the switching unit 401 and the ground terminal to generate a voltage drop. A signal output unit 402 and the switching unit 401 and the signal output unit 402 connected to the dropping means 405 and the voltage dropping means 405 to output a high level or low level signal through an output terminal. Is configured as a bias current unit 408 to maintain a constant current amount.

In this case, the switching unit 401 is the first and second transistors 401a and 401b driven by the input voltage Vin and the third and fourth transistors 401c and 401d driven by the reference voltage Vref. Consists of.

In addition, the signal output unit 402 is connected to the second transistor 401b and the ground terminal, and is driven by the voltage generated by the voltage drop means 405 and the fifth transistor 402a and the fifth. The sixth transistor 402b is connected to the transistor 402a and the ground terminal and driven by a power supply voltage VDD.

 In this case, the first to fourth transistors 401a to 401d are PNP transistors, and the fifth and sixth transistors 402a and 402b are NPN transistors.

The voltage drop means 405 is composed of seventh and eighth transistors 405a and 405b in a current mirror relationship, and the seventh and eighth transistors 405a and 405b are NPN transistors.

The reference voltage changing unit 411 may include a ninth transistor 412 connected to the third transistor 403 and a fourth transistor 404, and a first transistor connected in series with the ninth transistor 412. And a tenth transistor 414 connected to a resistor 413, the first resistor 413, and a ground terminal, and connected to a common terminal of the fifth and sixth transistors 406 and 407.

Here, the first resistor 413 is a variable resistor that can change the resistance value, and by changing the resistance value of the variable resistor, it is possible to accurately set the magnitude of the hysteresis voltage to be described later, and also to simplify the magnitude of the hysteresis voltage. It can also be changed.

In addition, the sixth transistor 402b is turned on if the voltage applied to the sixth transistor 402b is greater than the threshold voltage (usually 0.7V) of the sixth transistor 402b. Therefore, when all of the power supply voltages VDD are applied to the emitter of the sixth transistor 402b, a voltage greater than the standard voltage of the sixth transistor 402b is applied, so that the sixth transistor 402b may be damaged. There is. Accordingly, a second resistor 409 is connected between the collector of the fifth transistor 402a and the base of the tenth transistor 414, and the collector of the fifth transistor 402a and the sixth transistor 402b. The third resistor 410 may be connected between the bases of the transistors) to prevent an overvoltage from being applied to the emitter of the sixth transistor 402b.

When the voltage comparator according to the present invention having the above configuration outputs a high or low level signal by comparing the input voltage Vin and the reference voltage Vref, the process will be described in detail as follows.

First, when the input voltage Vin is smaller than the reference voltage Vref, the second transistor 401b is turned on and the third transistor 401c is turned off due to the characteristics of the PNP transistor, so that the bias current I to the voltage comparator. _1b flows into I _2b , whereby a voltage drop occurs in the voltage drop means 405, and a voltage having a predetermined magnitude is applied to the emitter of the fifth transistor 402a. At this time, since the magnitude of the voltage is greater than the magnitude of the threshold voltage of the fifth transistor 402a, the fifth transistor 402a is turned on.

Accordingly, the collector-emitter voltage of the fifth transistor 402a is applied to the emitter of the sixth transistor 402b, and the voltage is typically about 0.1V, so that the threshold voltage of the sixth transistor 402b Since it does not reach the size, the sixth transistor 402b is turned off. In this case, since the emitter of the sixth transistor 402b and the emitter 414 of the tenth transistor are connected, the collector-emitter voltage of the fifth transistor 402a is the same as that of the tenth transistor 414. It is also applied to the emitter and thus the tenth transistor 414 is also turned off. Therefore, when the input voltage Vin is smaller than the reference voltage Vref, the reference voltage changing unit 411 does not affect the voltage comparison path at all.

On the other hand, when the input voltage Vin is greater than the reference voltage Vref, the second transistor 401b is turned off and the third transistor 401c is turned on due to the characteristics of the PNP transistor, so that the bias current I to the voltage comparator. _1b flows to I _3b , and thus, the voltage drop does not occur to the voltage drop means 405, and thus the emitter voltage for turning on the fifth transistor 402a is not applied. 402a is turned off.

Accordingly, the power supply voltage VDD is applied to the emitter of the sixth transistor 402b, so that the sixth transistor 402b is turned on so that the output terminal of the sixth transistor 402b is turned on. A low level signal is output.

In this case, since the emitter of the sixth transistor 402b and the emitter of the tenth transistor 414 are connected, a power supply voltage VDD is also applied to the emitter of the tenth transistor 414. Ten transistors 414 are also turned on.

Accordingly, current flows through the ninth transistor 412, the first resistor 413, and the tenth transistor 414 so that the emitter voltage of the third transistor 401c is already generated in the ninth transistor 412. It can be expressed as a sum of a ter-base voltage (hereinafter, V _BE ), a voltage across the first resistor 413 (hereinafter, V _R1 ), and a collector-base voltage (hereinafter, Vsat) of the tenth transistor 414. From this point, the reference voltage is V _BE + V _R1 + Vsat (hereinafter referred to as Vref´). That is, FIG. 5 is a diagram illustrating hysteresis characteristics of a voltage comparison circuit according to the present invention, and FIG. 6 is a view illustrating an output signal according to input noise into a voltage comparison circuit according to the present invention. ) Shows the input voltage (Vin) and the reference voltage (Vref) when the noise is generated in the section where the reference voltage (Vref) is greater than, and (b) shows the output signal when the noise occurs will be. As shown in FIG. 5, the reference voltage when the output signal changes from the high level to the low level becomes Vref, which is a conventional reference voltage, but the reference voltage for changing the output signal from the low level to the high level is Vref '. Becomes

Therefore, once the output signal is changed from the high level to the low level, the signal of the high level is output from this time only when the input voltage Vin is smaller than Vref '. Have characteristics. In addition, as shown in FIG. 6, when the noise E smaller than the magnitude of the hysteresis voltage (difference between Vref and Vref ') occurs, the low level output is maintained without reacting to the noise E. FIG. .

As described above, according to the voltage comparison circuit having a hysteresis characteristic according to the present invention, by adding a reference voltage changer composed of a small number of elements into the circuit, it is possible to design a stable voltage comparison path against input noise. There is.

In addition, by configuring the reference voltage changer using a variable resistor, the magnitude of the hysteresis voltage can be accurately set by changing the resistance value, and the magnitude of the hysteresis voltage can be simply changed.

Claims (14)

A comparison unit comparing a reference voltage and an input voltage with each other and outputting a high level or low level signal; And And a reference voltage changer for changing the reference voltage when a low level output signal is generated from the comparator. The method of claim 1, wherein the comparison unit, A switching unit driven by the input voltage and the reference voltage; Voltage drop means connected to the switching unit and the ground terminal to generate a voltage drop; A signal output unit connected to the voltage drop unit to output a high level or low level signal through an output terminal; And And a bias current unit connected to the switching unit and the signal output unit to maintain a constant amount of current. The method of claim 2, wherein the switching unit, First and second transistors driven by the input voltage; And And a third transistor and a fourth transistor driven by the reference voltage. The method of claim 3, wherein the signal output unit, A fifth transistor connected to the second transistor and the ground terminal and driven with a voltage generated by the voltage drop means; And And a sixth transistor connected to the fifth transistor and the ground terminal and driven by a power supply voltage. The method of claim 4, wherein The first to fourth transistors are PNP transistors, and the fifth and sixth transistors are NPN transistors, characterized in that the hysteresis characteristics. The method of claim 2, wherein the voltage drop means, A voltage comparison inductor having hysteresis characteristics, comprising a seventh and eighth transistors in a current mirror relationship. The method of claim 6, And the seventh and eighth transistors are NPN transistors. The method of claim 5, wherein the reference voltage changing unit, A ninth transistor connected to the third transistor and a fourth transistor; A first resistor connected in series with the ninth transistor; And And a tenth transistor connected to the first resistor and the ground terminal and connected to a common terminal of the fifth and sixth transistors. The method of claim 8, wherein the comparison unit, When the input voltage is less than the reference voltage, the second and fifth transistors are turned on and the third and sixth transistors are turned off to output a high level signal through an output terminal. In voltage comparison. The method of claim 9, And the tenth transistor of the reference voltage changing unit is turned off. The method of claim 8, wherein the comparison unit, When the input voltage is greater than the reference voltage, the third and sixth transistors of the comparator are turned on and the second and fifth transistors are turned off to output a low level signal through an output terminal. Having voltage comparison. The method of claim 11, And the ninth and tenth transistors of the reference voltage changing unit are turned on. The method of claim 10 or 12, The first resistor is a voltage comparator having hysteresis characteristics, characterized in that the variable resistance that can change the resistance value. The method according to claim 10 or 12, in order to protect the sixth transistor, The second resistor is connected between the collector of the fifth transistor and the base of the tenth transistor, and the third resistor is connected between the collector of the fifth transistor and the base of the sixth transistor. Having voltage comparison.

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