Abstract:
A hysteresis circuit applied to a comparator and an amplifier circuit thereof are provided. A hysteresis circuit is disposed on a positive feedback path of the comparator, such that the comparator resists noise interferences, and the hysteresis circuit has a feature of not affecting the feedback voltage signal, thereby making the hysteresis range of the comparator be more precise.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The present invention relates to a hysteresis circuit. More particularly, the present invention relates to a hysteresis circuit applied to a comparator and an amplifier circuit thereof. 
         [0003]    2. Related Art 
         [0004]    In order to solve output misdeterminations of comparator circuits caused by noise interferences, usually a common method is using an internal circuit of a comparator and a positive feedback mechanism to generate the hysteresis, so as to achieve the function of noise resistance. Referring to  FIG. 1 , a schematic view of the signal converting of a common hysteresis circuit is shown, wherein a horizontal axis indicates an input voltage signal Vin, and a vertical axis indicates an output voltage signal Vout. When the output voltage signal Vout is a low level voltage Vol, the input voltage signal Vin must be raised till it is higher than an upper limit threshold voltage value Vth, the output voltage signal Vout is converted from the low level voltage Vol to a high level voltage Voh. 
         [0005]    When the output voltage signal Vout is the high level voltage Voh, the input voltage signal Vin must be lowered till it is lower than a lower limit threshold voltage value Vtl, the output voltage signal Vout is converted from the high level voltage Voh to the low level voltage Vol. Therefore, when the input voltage signal Vin of the comparator has the noise interference, through the hysteresis generated by the hysteresis circuit, the comparator does not tend to be interfered by the noise to generate misoperation. 
         [0006]    Next, referring to  FIG. 2A , a schematic view of a common hysteresis circuit is shown. Mainly, a hysteresis circuit  10  is disposed on a positive feedback path of a comparator  20 , such that the comparator  20  resists the noise interference, wherein a reference voltage signal Vref of the input comparator  20  is generated by a power source voltage regulator  30 , and the hysteresis circuit  10  is formed by a resistor R 1 . Although the hysteresis circuit  10  has the advantages of low cost and simple architecture, because the resistor R 1  is disposed, the input voltage signal Vin of the comparator  20  is affected by the resistor R 1 , a resistor R 2 , and a resistor R 3 , such that the precision of the hysteresis range of the comparator  20  is reduced. 
         [0007]    Therefore, another hysteresis circuit designing manner is generated, referring to  FIG. 2B , a schematic view of another hysteresis circuit is shown. It is designed mainly for the hysteresis circuit  11 , and the hysteresis circuit  11  is formed by the resistor R 1  and a diode D. In this manner, although the input voltage signal Vin of the comparator  20  is not affected by the resistor R 1 , because the diode D has a forward voltage drop, the precision of the hysteresis range of the comparator  20  is also reduced. 
         [0008]    Therefore, when the comparator adopts a common hysteresis circuit design, because of the features of the circuit elements in the hysteresis circuit, the hysteresis range of the comparator is affected and is not precise. 
       SUMMARY OF THE INVENTION 
       [0009]    In view of the above problems, the object of the present invention is to provide a hysteresis circuit applied to a comparator and an amplifier circuit thereof, such that the threshold comparison voltage of the comparator is not affected by the hysteresis circuit, thereby making the hysteresis range of the comparator be more precise. 
         [0010]    In the hysteresis circuit applied to the comparator disclosed according to the present invention, the comparator has a first input end, a second input end, and an output end. The first input end receives an input voltage signal, and the second input end receives a reference voltage signal. The comparator outputs a high level voltage signal or a low level voltage signal from the output end according to a difference between the input voltage signal and the reference voltage signal. The hysteresis circuit comprises a first resistor, a diode, and an operational amplifier. 
         [0011]    The first resistor is electrically coupled between the first input end and the output end of the comparator. The diode is electrically coupled to the first resistor. The operational amplifier has a first input end, a second input end, and an output end, and is electrically coupled between the diode and the output end of the comparator. The first input end of the operational amplifier receives the high level voltage signal or the low level voltage signal, and the output end of the operational amplifier outputs the high level voltage signal or the low level voltage signal, so as to increase the difference between the input voltage signal and the reference voltage signal of the comparator. 
         [0012]    The amplifier circuit disclosed according to the present invention comprises a first operational amplifier and a hysteresis circuit. 
         [0013]    The first operational amplifier has a first OP input end, a second OP input end, and an OP output end. The first OP input end receives an input voltage signal, and the second OP input end receives a reference voltage signal. The first operational amplifier outputs a high level voltage signal or a low level voltage signal from the OP output end according to a difference between the input voltage signal and the reference voltage signal. 
         [0014]    The hysteresis circuit is electrically coupled between the first input end and the output end of the first operational amplifier, wherein the hysteresis circuit comprises a first resistor, a diode, and a second operational amplifier. 
         [0015]    The first resistor is electrically coupled between the first input end and the output end of the first operational amplifier. The diode is electrically coupled to the first resistor. The second operational amplifier has a first input end, a second input end, and an output end, and is electrically coupled between the diode and the output end of the first operational amplifier. The first input end of the second operational amplifier receives the high level voltage signal or the low level voltage signal, and the output end of the second operational amplifier outputs the high level voltage signal or low level voltage signal, so as to increase the difference between the input voltage signal and the reference voltage signal of the first operational amplifier. 
         [0016]    By using the hysteresis circuit applied to the comparator and the amplifier circuit thereof, and using the feature that the operational amplifier and the diode forms a super diode circuit, the diode forward voltage drop in the former hysteresis circuit is nearly zero. In this manner, a feedback voltage signal of the comparator is not affected by the hysteresis circuit, thereby improving the precision of the hysteresis range of the comparator. Compared with the conventional hysteresis circuit design, the hysteresis circuit architecture of the present invention is achieved by only disposing an operational amplifier, and thus it has a simple circuit architecture. 
         [0017]    The features and practices of the present invention are illustrated in detail below through the preferred embodiments with the accompanying drawings. 
         [0018]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The present invention will become more fully understood from the detailed description given herein below for illustration only, and thus is not limitative of the present invention, and wherein: 
           [0020]      FIG. 1  is a schematic view of the signal converting of a hysteresis circuit according to the prior art; 
           [0021]      FIG. 2A  is a schematic view of the hysteresis circuit according to the prior art; 
           [0022]      FIG. 2B  is a schematic view of another hysteresis circuit according to the prior art; 
           [0023]      FIG. 3  is a schematic view of the hysteresis circuit according to an embodiment of the present invention; and 
           [0024]      FIG. 4  is a schematic view of the amplifier circuit according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    Referring to  FIG. 3 , a schematic view of the hysteresis circuit according to an embodiment of the present invention is shown. As shown in  FIG. 3 , the hysteresis circuit  12  of the present invention includes a first resistor R 1 , a diode D, and an operational amplifier OP. The illustration of the connecting relationship of each circuit element is given as follows. 
         [0026]    The first resistor R 1  has a first end and a second end, the first end of the first resistor R 1  is electrically coupled to a subsequent stage circuit, and the second end of the first resistor R 1  is electrically coupled to an output end of the diode D. 
         [0027]    The diode D has an input end (i.e. a positive end) and an output end (i.e. a negative end), the input end of the diode D is electrically coupled to an output end of the operational amplifier OP, and the output end of the diode D is electrically coupled between the second end of the first resistor R 1  and a second input end of the operational amplifier OP. 
         [0028]    The operational amplifier OP has a first input end (i.e. a positive phase input end), a second input end (i.e. a negative phase input end), and an output end. The first input end of the operational amplifier OP is electrically coupled to a previous stage circuit, the second input end of the operational amplifier OP is electrically coupled to the output end of the diode D, and the output end of the operational amplifier OP is electrically coupled to the input end of the diode D. 
         [0029]    Next, referring to  FIG. 4 , a schematic view of the amplifier circuit according to the embodiment of the present invention is shown. As shown in  FIG. 4 , the amplifier circuit of the present invention includes a first operational amplifier OP 1  and a hysteresis circuit  12 . The illustration of the connecting relation of each circuit element is given as follows. 
         [0030]    The first operational amplifier OP 1  has a first input end (i.e. a positive phase input end), a second input end (i.e. a negative phase input end), and an output end. The first input end of the first operational amplifier OP 1  is electrically coupled to the first end of the first resistor R 1 , a second end of a second resistor R 2 , and a first end of a third resistor R 3 . The second input end of the first operational amplifier OP 1  is electrically coupled to the power source voltage regulator  30 , and receives the reference voltage signal Vref output by the power source voltage regulator  30 . The output end of the first operational amplifier OP 1  is electrically coupled to the first input end of a second operational amplifier OP 2  and a first end of a fourth resistor R 4 . 
         [0031]    A first end of the second resistor R 2  receives an input voltage signal Vin, a second end of the third resistor R 3  is electrically coupled to a ground end, and a second end of the fourth resistor R 4  provides an output voltage signal Vout. The second operational amplifier OP 2  has a first input end (i.e. a positive phase input end), a second input end (i.e. a negative phase input end), and an output end. The first input end of the second operational amplifier OP 2  is electrically coupled to the output end of the first operational amplifier OP 1  and the first end of the fourth resistor R 4 . The second input end of the second operational amplifier OP 2  is electrically coupled to the output end of the diode D. The output end of the second operational amplifier OP 2  is electrically coupled to the input end of the diode D. The output end of the diode D is electrically coupled to the second end of the first resistor R 1  and the second input end of the second operational amplifier OP 2 . 
         [0032]    The power source voltage regulator  30  includes a Zener diode ZD, a fifth resistor R 5 , a sixth resistor R 6 , and a capacitor C. 
         [0033]    Firstly, a first end of the capacitor C is electrically coupled to a first end of the fifth resistor R 5 , and a second end of the capacitor C is electrically coupled to a second end of the sixth resistor R 6 . The first end of the fifth resistor R 5  is electrically coupled to a first end (i.e. a negative end) of the Zener diode ZD, the second input end of the first operational OP 1 , and a second end of a seventh resistor R 7 . A second end of the fifth resistor R 5  is electrically coupled to a third end of the Zener diode ZD and a first end of the sixth resistor R 6 . A second end of the sixth resistor R 6  is electrically coupled to a second end (i.e. a positive end) of the Zener diode ZD and the ground end. The capacitor C, the fifth resistor R 5 , and the sixth resistor R 6  form a parallel loop, and the fifth resistor R 5 , the sixth resistor R 6 , and the Zener diode ZD form a parallel loop. 
         [0034]    The circuit operation principle is illustrated as follows. 
         [0035]    When the first input end of the first operational amplifier OP 1  receives the input voltage signal Vin, the first operational amplifier OP 1  compares the input voltage signal Vin and the reference voltage signal Vref. When the input voltage signal Vin is larger than the reference voltage signal Vref, the output end of the first operational amplifier OP 1  outputs the high level voltage signal Voh. After the high level voltage signal Voh is input to the first input end of the first operational amplifier OP 1  through the feedback path formed by the second operational amplifier OP 2 , the diode D, and the first resistor R 1 , the difference value between the input voltage signal Vin and the reference voltage signal Vref input to the first operational amplifier OP 1  is increased. In this manner, the output of the first operational amplifier OP 1  is not interfered by the noise to generate misoperation. 
         [0036]    Similarly, when the input voltage signal Vin is less than the reference voltage signal Vref, the output end of the first operational amplifier OP 1  outputs the low level voltage signal Vol. After the low level voltage signal Vol is input to the first input end of the first operational amplifier OP 1  through the feedback path formed by the second operational amplifier OP 2 , the diode D, and the first resistor R 1 , the difference value between the input voltage signal Vin and the reference voltage signal Vref input to the first operational amplifier OP 1  is increased. In this manner, the output of the first operational amplifier OP 1  is not interfered by the noise to generate misoperation. 
         [0037]    The second operational amplifier OP 2  and the diode in the hysteresis circuit  12  form a super diode circuit, so the forward voltage drop of the diode D is nearly zero. Therefore, the hysteresis circuit  12  may not affect the feedback voltage signal input to the first operational amplifier OP 1 . 
         [0038]    To sum up, the hysteresis circuit applied to the comparator and the amplifier circuit thereof according to the present invention mainly can solve the problem that the hysteresis circuit formed by the positive feedback resistor and the diode affects the feedback voltage signal, such that the hysteresis ranges of the comparator is more precise. 
         [0039]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.