JP3623624B2 - Hysteresis comparator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hysteresis comparator for converting an analog signal into a digital signal.
[0002]
[Prior art]
When comparing the level of an analog signal with noise to a reference voltage using a comparator and converting it to a digital signal according to the determination result, the comparator has hysteresis to prevent erroneous determination due to noise. Is generally set.
[0003]
FIG. 7 is a block diagram of this type of conventional hysteresis comparator. The hysteresis comparator 71 achieves hysteresis characteristics by applying positive feedback from the output of the comparator 72 via a resistor. Here, the hysteresis width and the threshold voltage are determined by the reference voltage Vc, the output voltage of the comparator 72, and the ratio of the positive phase input resistance and the feedback resistance.
[0004]
Hysteresis comparators are intended to prevent false judgments due to noise, but noise itself is susceptible to circuit mounting conditions, signal line wrapping, and changes in environmental conditions. It is difficult to identify. Therefore, in particular, when a hysteresis comparator is built in a semiconductor integrated circuit, the hysteresis width may have a circuit configuration that can be adjusted outside the semiconductor integrated circuit. In the case of the conventional circuit, the hysteresis width can be changed by changing the ratio of the input resistance and the feedback resistance. Therefore, any one of the resistors is placed outside the semiconductor integrated circuit and adjusted by changing the resistance value. It was generally done.
[0005]
However, since the threshold voltage also changes when the hysteresis width is changed in the conventional circuit, a reference voltage input terminal is provided as an external terminal of the semiconductor integrated circuit for the purpose of changing the threshold voltage, and the reference voltage is adjusted externally. I had to.
In order to solve this problem, several techniques for facilitating adjustment of the hysteresis width and the threshold voltage by attaching an amplifier or the like to the hysteresis comparator have been proposed.
[0006]
For example, Japanese Utility Model Laid-Open No. 2-28133 discloses a hysteresis provided with first and second comparators, an exclusive NOR circuit for inputting each output voltage thereof, and a flip-flop circuit having the output as an input. A comparator is disclosed. In this hysteresis comparator, an input voltage is input to the first input terminal of the first comparator, a setting voltage that is an upper limit voltage of hysteresis is input to the second input terminal, and an input voltage is input to the first input terminal of the second comparator. Is configured to input a set voltage as a lower limit voltage of hysteresis to the second input terminal. Then, using the rise or fall of the output voltage of the exclusive NOR circuit as a trigger, the output of one of the above comparators is taken into a flip-flop and used as an output. In this conventional technique, the upper limit and the lower limit of the hysteresis can be easily changed by changing the two set voltages.
[0007]
However, the technique disclosed in the above publication has a problem from the viewpoint of eliminating the influence of noise. The case where the input voltage transitions gently over time will be described as an example. In the hysteresis comparator having the above-described configuration, the two comparators themselves do not have hysteresis characteristics. In the vicinity where the input voltage crosses, the comparator may cause chattering by repeating high and low due to noise. The generated chattering does not disappear even if the exclusive NOR of the output of the comparator is taken or through the delay circuit, and appears in the output as it is.
[0008]
On the other hand, when the input voltage changes sharply in time, that is, in the case of a pulse-like input, the chattering problem as described above does not occur. However, since noise is present in the high and low periods of the pulse, malfunction may occur if the noise exceeds the threshold voltage of the comparator. In a normal hysteresis comparator, the noise margin is expanded by lowering the comparison voltage when the input is high and increasing the comparison voltage when the input is low. Therefore, if the hysteresis width is widened, the noise margin is also widened. On the other hand, in the hysteresis comparator described in the above publication, the noise margin is not widened as the hysteresis width is widened. Therefore, the possibility of the above malfunction cannot be excluded.
[0009]
Japanese Patent Laid-Open No. 64-30320 discloses that an inverting input of a comparator is an input terminal, an output is input to an amplifier, and two impedance elements are connected in series between the output of the amplifier and the input terminal. A hysteresis comparator having a circuit configuration in which is connected to the non-inverting input of the comparator is disclosed. In this circuit, the hysteresis width can be adjusted by changing the ratio of the feedback resistance and the input resistance of the comparator. On the other hand, the threshold voltage (center voltage of hysteresis voltage) can be adjusted by changing the voltage supplied from the outside to the input resistance. However, if either the feedback resistance or the input resistance is changed in order to change the hysteresis width, the threshold voltage also changes, so that each cannot be adjusted independently.
[0010]
In addition, when adjusting the circuit having this configuration in a semiconductor integrated circuit, either one of the feedback resistor and the input resistor, or both of them are arranged outside the semiconductor integrated circuit, or several types of resistors are set in advance. It is necessary to take measures such as selecting a resistor having an optimum resistance value built in a semiconductor integrated circuit. If the adjustment is made outside the semiconductor integrated circuit, the number of terminals and external parts will increase. On the other hand, if the adjustment is made inside the semiconductor integrated circuit, an adjustment circuit must be added. However, there is a problem that the circuit scale must be large.
[0011]
[Problems to be solved by the invention]
In a conventional general hysteresis comparator, a comparison voltage is generated using the output of the comparator. If a comparison voltage can be generated and supplied to the comparator regardless of the output of the comparator, the hysteresis width and threshold voltage can be set independently. However, if chattering occurs or the noise margin is lost, the original function of the hysteresis comparator is impaired.
[0012]
Accordingly, an object of the present invention is to provide a hysteresis comparator capable of independently setting the hysteresis width and the threshold voltage without impairing the original function of the hysteresis comparator for preventing malfunction due to noise.
[0013]
The present invention compares the input voltage supplied to one input terminal with the threshold voltage supplied to the other input terminal by comparing the amplifier that inputs the input voltage and outputs the threshold voltage. A hysteresis comparator having a comparator for outputting the comparison result, wherein the amplifier is capable of inputting a first arbitrary voltage and an inverting input terminal to which the input voltage is supplied and a non-inverting input terminal. A current dividing type gain variable circuit having a width setting terminal; a level shift circuit that shifts an output voltage of the current dividing type gain variable circuit; and a feedback circuit, wherein the feedback circuit supplies a second arbitrary voltage. It has a threshold voltage setting terminal that can be input, and the output voltage of the level shift circuit is divided by a resistor inserted between the level shift circuit and the threshold voltage setting terminal. And outputs the output voltage as the threshold voltage and inputs to the non-inverting input terminal.
[0014]
Further, the current dividing type gain variable circuit has a function of changing a gain by a voltage difference between the first arbitrary voltage and a reference voltage.
[0015]
Further, the current division type variable gain circuit has a bias circuit for generating the reference voltage.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram illustrating an outline of a configuration of a hysteresis comparator 1 in the embodiment. The hysteresis comparator 1 includes a comparator 2 and an amplifier 3. The input terminal 11 (Vin) of the hysteresis comparator 1 is connected to the inverting input terminal (Vin−) of the variable gain amplifier 4 in the amplifier 3 and the inverting input terminal (−) of the comparator 2. The amplifier 3 further includes two input terminals, a hysteresis width setting terminal 31 and a threshold voltage setting terminal 32.
[0017]
FIG. 2 is a circuit diagram illustrating a more detailed configuration of the hysteresis comparator 1. In FIG. 2, the amplifier 3 divides the output voltage of the variable gain amplifier 4, the level shift circuit 5 that shifts the output voltage of the variable gain amplifier 4, and the output voltage of the level shift circuit 5 by a resistor, The feedback circuit 6 applies positive feedback to the input terminal (Vin +). The variable gain amplifier 4 is provided with a bias circuit 41, and a reference voltage Vc is supplied from the bias circuit 41 and a voltage Va is supplied from the hysteresis width setting terminal 31. The feedback circuit 6 is supplied with the voltage Vb from the threshold voltage setting terminal 32.
[0018]
In the hysteresis comparator 1 having the above configuration, the hysteresis width and the threshold voltage can be set independently. The reason will be described below with reference to FIGS. In the gain conversion amplifier 4 in the embodiment, a differential pair for performing fluctuation control of the output DC potential is added to the amplifier to constitute a current division type gain variable circuit. It is known that the variable gain amplifier having such a configuration changes the maximum output amplitude with the gain without changing the center potential of the output amplitude.
[0019]
FIG. 3 shows from the input [(Vin +) − (vin−)] of the variable gain amplifier 4 to the output Vo of the level shift circuit 5 when the positive feedback loop by the feedback circuit 6 is disconnected and the voltage between Va and Vc is changed. It is a figure showing the gain variable characteristic showing the gain of. Since the level shift circuit 5 only shifts the output of the variable gain amplifier 4, the characteristic shown in FIG. 3 can be said to be the characteristic of the variable gain amplifier 4 itself. The variable gain amplifier 4 is a circuit capable of changing the gain by the difference voltage between the hysteresis setting voltage Va and the reference voltage Vc. The gain increases as Va-Vc decreases, that is, the direction from V1 to V4. Conversely, the gain decreases as Va-Vc decreases, that is, the direction decreases from V4 to V1. The maximum value of the gain is determined by the maximum output voltage range of the variable gain amplifier 4, and the minimum value is a state where nothing is output to the output even when there is an input, that is, an infinitely small value.
[0020]
FIG. 4 shows a state of the output Vo of the level shift circuit 5 when the positive feedback loop by the feedback circuit 6 is disconnected, the fixed voltage Vin + is applied to the non-inverting input of the variable gain amplifier 4 and the voltage Vin− of the inverting input is changed. It is a figure showing the direct-current transfer characteristic showing. V1 to V4 in FIG. 4 correspond to the Va-Vc differential voltage in FIG. When V1 is an infinitely small gain condition, the output Vo is constant regardless of the inverting input voltage Vin−, and the amplitude change ΔVo of the output voltage centering on Vo increases as the Va−Vc differential voltage increases from V1 to V4. The DC transfer characteristic is increased.
[0021]
In this embodiment, by utilizing the characteristics of the variable gain amplifier 4 shown in FIGS. 3 and 4, a hysteresis comparator that can easily adjust the hysteresis width and the threshold voltage independently can be realized. Yes.
In order to simplify the description, it is assumed below that the two resistances of the feedback circuit 6 have the same resistance value R as shown in Equation (1).
[0022]
[Expression 1]
(Vo−Vt) / R = (Vt−Vb) / R
[0023]
In this case, the threshold voltage Vt is given by Equation 2 from the output voltage Vo and the threshold voltage setting voltage Vb.
[0024]
[Expression 2]
Vt = 1/2 (Vo + Vb)
[0025]
Similarly, the hysteresis width 2ΔVt is derived from Equation 3 to Equation 4 from the amplitude change ΔVo of the output voltage.
[Equation 3]
[Vo + ΔVo− (Vt + ΔVt)] / R = (Vt + ΔVt−Vb) / R
[Expression 4]
2ΔVt = Vo + ΔVo−2Vt + Vb
[0026]
Substituting Equation 1 into Equation 4 yields Equation 5 below.
[0027]
[Equation 5]
2ΔVt = ΔVo
[0028]
As shown in FIG. 4, since the center voltage of the output amplitude of the level shift circuit 5 is constant at Vo regardless of the gain, the voltage Vb at the threshold voltage setting terminal 32 is obtained from the equation (2). It can be seen that it can only be set with. Further, from the equation (5), it can be seen that the hysteresis width 2ΔVt is equal to ΔVo, and half of the output amplitude of the variable gain amplifier 4 is the hysteresis width. Since the output amplitude of the variable gain amplifier 4 changes by changing the gain as shown in FIGS. 3 and 4, the hysteresis width can be set only by the voltage Va at the hysteresis width setting terminal 31.
[0029]
FIG. 5 is a diagram illustrating changes in hysteresis characteristics when Vb is fixed and Va is changed as an example of the hysteresis width adjustment. FIG. 5 shows that the hysteresis width is changed by changing Va without changing the threshold voltage. Similarly, FIG. 6 shows changes in threshold voltage when Va is fixed and Vb is changed as an example of threshold voltage adjustment. FIG. 6 shows that the threshold voltage changes without changing the hysteresis width.
[0030]
【The invention's effect】
As described above, the hysteresis comparator of the present invention can set the threshold voltage and the hysteresis width independently without requiring a troublesome operation such as changing the resistance. The setting operation can be easily performed by changing each setting voltage.
[0031]
In addition, the hysteresis comparator of the present invention can adjust the hysteresis characteristics in the same way even when built in a semiconductor integrated circuit, and it is necessary to add an external component and a circuit for adjustment as in the past. Therefore, it can be said that the hysteresis comparator is suitable for a semiconductor integrated circuit.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an outline of a configuration of a hysteresis comparator 1 according to an embodiment.
2 is a circuit diagram illustrating a detailed configuration of a hysteresis comparator 1. FIG.
3 is a graph showing variable gain characteristics from the input of variable gain amplifier 4 to the output of level shift circuit 5 when only the voltage between Va and Vc in FIG. 2 is changed;
4 is a diagram illustrating a DC transfer characteristic of an output of the level shift circuit 5 when a fixed voltage is applied to the non-inverting input of the variable gain amplifier 4 in FIG. 2 and only the voltage of the inverting input is changed.
FIG. 5 is a diagram illustrating a change in hysteresis characteristics when Vb in FIG. 2 is fixed and Va is changed.
6 is a diagram showing a change in threshold voltage when Vb in FIG. 2 is changed. FIG.
FIG. 7 is a diagram illustrating a configuration of a conventional hysteresis comparator.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Hysteresis comparator 2 Comparator 3 Amplifier 4 Gain variable amplifier 5 Level shift circuit 6 Feedback circuit 11 Input terminal 12 Output terminal 31 Hysteresis width setting terminal 32 Threshold voltage setting terminal

Claims (3)

Comparison between the amplifier for inputting an input voltage and outputting a threshold voltage and the input voltage supplied to one input terminal and the threshold voltage supplied to the other input terminal A comparator that outputs a comparator,
The amplifier includes a current dividing type gain variable circuit having an inverting input terminal to which the input voltage is supplied, a non-inverting input terminal, and a hysteresis width setting terminal capable of inputting a first arbitrary voltage, and the current dividing A level shift circuit that shifts the output voltage of the variable gain circuit, and a feedback circuit,
The feedback circuit has a threshold voltage setting terminal to which a second arbitrary voltage can be input, and the output voltage of the level shift circuit is inserted between the level shift circuit and the threshold voltage setting terminal. A hysteresis comparator, wherein an output voltage divided by a resistor is input to the non-inverting input terminal and output as the threshold voltage. 4. The hysteresis comparator according to claim 3, wherein the current dividing type gain variable circuit has a function of changing a gain by a difference voltage between the first arbitrary voltage and a reference voltage. 5. The hysteresis comparator according to claim 4, wherein the current-dividing gain variable circuit includes a bias circuit that generates the reference voltage.

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