Abstract:
The present invention discloses an offset cancellation current mirror and method thereof. The offset cancellation current minor comprises a first current mirror, a second current minor, switches and resistors. The first current minor comprises two transistors and a capacitance, the capacitance is used to store an electrical potential difference when the switches are turned on in ways of connecting the first current mirror with the resistor. When the switches is turned off in ways of disconnecting the first current mirror with the resistor and connecting the first current mirror with the second current minor, the electrical potential difference stored in the capacitance is used to correct the difference of the two transistors due to manufacture process.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The exemplary embodiment(s) of the present invention relates to a field of offset cancellation current minor and an operating method thereof. More specifically, the exemplary embodiment(s) of the present invention relates to an offset cancellation current mirror and an operating method thereof of cancelling the offset voltage between a current mirror pair. 
     2. Description of Related Art 
     As is well known in the art, the current minor offers an accurate reproduction of the reference based on the fine distinction between the reference current and the corresponding current. The magnitude of the offset voltages is inversely proportional to the scale of the respective transistor. The smaller the transistor, the larger the offset voltage. However, the improvement of the manufacture technology contributes to the smaller scale of the transistor. Thus, the request of the stable current in the current minor and the yield rate of semiconductor manufacture procedure are the urgent problems to be solved. 
     SUMMARY OF THE INVENTION 
     In view of the aforementioned problems of the prior art, one objective of the present invention is to provide an offset cancellation current minor and operating method thereof to cancel the distinction between the reference current and the corresponding current. 
     According to the objective, the present invention provides an offset cancellation current minor comprising a first current mirror, a first resistor, a second resistor, and a second current minor. The first current comprises a first reference current input terminal, a first reference current output terminal, a first corresponding current input terminal, a first corresponding current output terminal, a first transistor, a second transistor, a first switch, a second switch, a first capacitor and a second capacitor. 
     The first switch is connected between the gate of the first transistor and the drain of the first transistor. The second switch is connected between the gate of the second transistor and the drain of the second transistor. The first capacitor is connected between the drain of the first transistor and the gate of the second transistor. The second capacitor is connected between the gate of the first transistor. The drain of the first transistor, the source of the first transistor and the drain of the first transistor are connected to the first reference current input terminal and the first reference current output terminal respectively, and the source of the second transistor and the drain of the second transistor are connected to the first corresponding current input terminal and the first corresponding current output terminal respectively. 
     The third switch has a first lower access point and a first upper access point connected to the first reference current output terminal. The fourth switch has a second lower access point and a second upper access point connected to the first corresponding current output terminal. The first resistor is connected between the first lower access point of the third switch and a grounding terminal. The second resistor is connected between the second lower access point of the fourth switch and the grounding terminal. The fifth switch has a third lower access point and a third upper access point connected to the first reference current output terminal. The sixth switch has a fourth lower access point and a fourth upper access point connected to the first corresponding current output terminal. The second current minor comprises a second reference current input terminal, a second reference current output terminal, a second corresponding current input terminal, a second corresponding output terminal, a third transistor and a fourth transistor. The gate of the third transistor is connected to the gate of the fourth transistor and the drain of the third transistor. The second reference current input terminal is connected to the source of the third transistor and the third lower access point of the fifth switch. The second corresponding current input terminal is connected to the source of the fourth transistor and the fourth lower access point of the sixth switch. 
     According to the objective, the present invention provides an operating method of offset cancellation current minor comprising the following steps. Firstly, a first minor current mirror is provided, and the first mirror current comprises a first reference current input terminal, a first reference current output terminal, a first corresponding current input terminal, a first corresponding current output terminal, a first transistor, a second transistor, a first capacitor and a second capacitor. The first switch is connected between the gate of the first transistor and the drain of the first transistor. The second switch is connected between the gate of the second transistor and the drain of the second transistor. The first capacitor is connected between the drain of the first transistor and the gate of the second transistor. The second capacitor is connected between the gate of the first transistor and the drain of the first transistor. The source of the first transistor and the drain of the first transistor are connected to the first reference current input terminal and the first reference current output terminal respectively. The source of the second transistor and the drain of the second transistor are connected to the first corresponding current input terminal and the first corresponding current output terminal respectively. 
     Provide a third switch connected between the first reference current output terminal and a first resistor, and provide a fourth switch connected between the first corresponding current the a second resistor. 
     Provide a second current minor comprising a second reference current input terminal, a second reference current output terminal, a second corresponding current input terminal, a second corresponding output terminal, a third transistor and a fourth transistor. The gate of the third transistor is connected to the gate of the fourth transistor and the drain of the third transistor. The second reference current input terminal is connected to the source of the third transistor. The second corresponding current input terminal is connected to the source of the fourth transistor. 
     Connect a fifth switch between the first reference current output terminal and the second reference current input terminal, and connect a sixth switch between the first corresponding current output terminal and the second corresponding current terminal. 
     Switch on the first switch, the second switch, the third switch and the fourth switch and switch off the fifth switch and sixth switch to inject a reference current into the first resistor through the first transistor and to inject a corresponding current into the second resistor through the second transistor for generating a potential difference between two nodes of the first capacitor. 
     Switch on the fifth switch and the sixth switch and switch off the first switch, the second switch, the third switch and the fourth switch to force the reference current flowing through the first transistor and the third transistor and to force the corresponding current flowing through the second transistor and the fourth transistor for maintaining the same voltage difference value of the first capacitor and the drain of the first transistor to keep the same potential difference. 
     As described above, the offset cancellation current minor and operating method thereof according the present invention may have the following advantages: 
     The offset cancellation current minor and operating method thereof may store the potential difference by the first capacitor to calibrate the manufacture inaccuracy of the current mirror. The smaller scale of the transistors, the influence due to the current distinction may increase. The influence may be decreased effectively by the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The exemplary embodiment(s) of the present invention will be understood more fully from the detailed description given below and from the accompanying drawings of various embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments, but are for explanation and understanding only. 
         FIG. 1  illustrates a schematic diagram of an offset cancellation current mirror in accordance with the present invention; 
         FIG. 2  illustrates a circuit diagram of an offset cancellation current minor in accordance with one embodiment of the present invention; and 
         FIG. 3  illustrates a flowchart of an operating method of offset cancellation current minor in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present invention are described herein in the context of an offset cancellation current minor and the operating method thereof. 
     Those of ordinary skilled in the art will realize that the following detailed description of the exemplary embodiment(s) is illustrative only and is not intended to be in any way limiting. Other embodiments will readily suggest themselves to such skilled persons having the benefit of this disclosure. Reference will now be made in detail to implementations of the exemplary embodiment(s) as illustrated in the accompanying drawings. The same reference indicators will be used throughout the drawings and the following detailed description to refer to the same or like parts. 
     Referring to  FIG. 1  and  FIG. 2 , a schematic diagram and a circuit diagram of the preferred embodiment of an offset cancellation current mirror according to the present invention are illustrated. In  FIG. 1 , the offset cancellation current mirror comprises a first minor current  11 , a second mirror current  12 , a first switch S 1 , a second switch S 2 , a third switch  13 , a fourth switch  14 , a fifth switch  15 , a sixth switch  16 , a first resistor  17 , a second resistor  18 , a first load  19  and a second load  20 . The third switch  13  and the fourth switch  14  are switched on, and the fifth switch  15  and the sixth switch  16  are switched off in order to connect the first minor current  11  to the first resistor  17  and the second resistor  18  via the third switch  13  and the fourth switch  14 . Then the third switch  13  and the fourth switch  14  are switched off, and the fifth switch  15  and sixth switch  16  are switched on in order to connect the first minor current  11  to the second minor current  12  via the fifth switch  15  and sixth switch  16 . The first load  19  and the second load  20  are connected to the second mirror current  12  for generating a corresponding current by the first mirror current  11  and the second mirror current  12 . 
     In  FIG. 2 , the first minor current  11  has a first reference current input terminal, a first reference current output terminal, a first corresponding current input terminal, a first corresponding current output terminal, a first transistor M 1 , a second transistor M 2 , a first switch S 1 , a second switch S 2 , a first capacitor C 1  and a second capacitor C 2 . The first switch S 1  is connected between the gate and the drain of the first transistor M 1 . The second switch S 2  is connected between the gate and the drain of the second transistor M 2 . The first capacitor C 1  is connected between the drain of the first transistor M 1  and the gate of the second transistor M 2 . The second capacitor C 2  is connected between the gate and the drain of the first transistor M 1 . The first reference current input terminal is connected the source of the first transistor M 1 . The first reference current output terminal is connected to the drain of the first transistor M 1 . The corresponding current input terminal is connected to the source of the second transistor M 2 . The first corresponding current input terminal is connected to the drain of the second transistor M 2 . 
     The third switch S 3  has a first lower access point and a first upper access point connected to the first reference current output terminal. The fourth switch S 4  has a second lower access point and a second upper access point connected to the first corresponding current output terminals. The first resistor R 1  is connected between the first lower access point of the third switch S 3  and a grounding terminal. The second resistor is connected to the second lower access point of the fourth switch S 4  and the grounding terminal. The fifth switch S 5  has a third lower access point and a third upper access point connected to the first reference current output terminal. The sixth switch S 6  has a fourth lower access point and a fourth upper access point connected to the first corresponding current output terminal. 
     The second current mirror  12  has a second reference current input terminal, a second reference current output terminal, a second corresponding current input terminal, a second corresponding current output terminal, a third transistor M 3 , and a fourth transistor M 4 . The gate of the third transistor M 3  is connected to the gate of the fourth transistor M 4 . The gate of the third transistor M 3  is connected to the drain of the third transistor M 3 . The second reference current input terminal is connected to the source of the third transistor M 3 . The second corresponding current input terminal is connected to the source of the fourth transistor M 4 . The second reference current input terminal is connected to the third lower access point of the fifth switch S 5 . The second corresponding current input terminal is connected to the fourth lower access point of the sixth switch S 6 . The first load R 3  is connected to the second reference current output terminal. The second load R 4  is connected to the corresponding current output terminal. 
     When the fifth switch S 5  and sixth switch S 6  are switched off and the first switch S 1 , second switch S 2 , third switch S 3  and the fourth switch are switched on at the same time, a reference current is injected into the first transistor M 1  and second transistor M 2 . A potential difference between two nodes of the first capacitor C 1  may be generated. The voltage value of the potential difference is the voltage value difference of the gate of the first transistor M 1  and the gate of the second transistor M 2 . 
     When the switch S 5  and sixth switch are switched on, the first switch S 1 , second switch S 2 , third switch S 3  and fourth switch S 4  are switched off; the first current minor  11  is connected to the second current mirror  12  instead of the first resistor R 1  and the second resistor R 2 . The current value of the reference current and current value of the corresponding current is changed corresponding to the connection of the first current minor and the second current mirror, the change of the first load R 3  and the change of the load R 4 . Thus, the voltage of the gate of the first transistor M 1  is changed. The second capacitor C 2  is connected to the gate of the first transistor M 1  and the first capacitor C 1  due to the switching off. Thus, the voltage of the first capacitor C 1  and the drain of the first transistor M 1  are the same. And the potential difference is kept the same. 
     Referring to  FIG. 3 , a flowchart of an operating method of offset cancellation current minor in accordance with the present invention is illustrated. The operating method of offset cancellation current mirror comprises the step of:
         In step S 10 , a first mirror current mirror is provided, and the first minor current comprises a first reference current input terminal, a reference current output terminal, a first corresponding current input terminal, a first corresponding current output terminal, a first capacitor and second capacitor.   In step S 20 , a third switch is connected between the first reference current output terminal and the first resistor, and a fourth switch is connected between the corresponding output terminal and the second resistor.   In step S 30 , a second current minor is provided, which has a second reference current input terminal, a second reference current output terminal and a second corresponding current input terminal.   In the step S 40 , a fifth switch is provided to be connected between the first reference current output terminal and the reference current input terminal. A sixth is provided to be connected between the first reference current output terminal and the corresponding current input terminal.   In the step S 50 , the first, second, third and fourth switched is switched on, and the fifth and the sixth switch is switched off for generating a potential difference between two nodes of the first capacitor.   In the step S 60 , the fifth switch and sixth switch are switched on, and the first switch, second switch, third switch and fourth switch are switched off to keep the same potential difference.       

     While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from this invention and its broader aspects. Therefore, the appended claims are intended to encompass within their scope of all such changes and modifications as are within the true spirit and scope of the exemplary embodiment(s) of the present invention.