Impedance matching circuit

Abstract

The present invention discloses an impedance matching circuit for facilitating impedance matching between the characteristic impedance of a cable and the input impedance at the input terminal of a receiver for data transmission comprising: a first transistor, a second transistor, a resistor, a negative feedback control circuit, a multiplexer and a reference voltage generator. When the characteristic impedance of the cable varies, the equivalent resistance of the impedance matching circuit can be kept equal to the resistance of the varied characteristic impedance of the cable by adjusting the reference voltage.

1. An impedance matching circuit for facilitating impedance matching between the characteristic impedance of a cable and the input impedance at the input terminal of a receiver for data transmission, said impedance matching circuit comprises  comprising:
 a first transistor, including a power supply terminal, a control terminal and a load terminal, wherein said power supply terminal of said first transistor is connected to a voltage supply, and said load terminal of said first transistor is connected to an input terminal of said receiver;  
 a second transistor, including a power supply terminal, a control terminal and a load terminal, wherein said power supply terminal of said second transistor is connected to said voltage supply, and said control terminal of said second transistor is connected to said control terminal of said first transistor;  
 a resistor, wherein one terminal of said resistor is connected to said load terminal of said second transistor and the other terminal is connected to the ground; and  
 a negative feedback control circuit, wherein an inverting input terminal of said negative feedback control circuit receives an adjustable reference voltage, a non-inverting input terminal of said negative feedback control circuit is connected to said load terminal of said second transistor, and an output terminal of said negative feedback control circuit is connected to said control terminal of said second transistor;  
 wherein the equivalent resistance of said impedance matching circuit is kept equal to the resistance of the varied characteristic impedance of said cable by adjusting said reference voltage.  
 
     
     
       2. The impedance matching circuit as recited in  claim 1 , wherein said first transistor is a p-channel MOSFET. 
     
     
       3. The impedance matching circuit as recited in  claim 1 , wherein said second transistor is a p-channel MOSFET. 
     
     
       4. The impedance matching circuit as recited in  claim 1 , further comprising: a multiplexer, including a select terminal and a signal output terminal; wherein said multiplexer receives a plurality of voltage signals having different magnitudes, selects one from said plurality of voltage signals according to a select signal received by said select terminal, and then outputs said voltage signal as said reference voltage into said inverting input terminal of said negative feedback control circuit. 
     
     
       5. The impedance matching circuit as recited in  claim 4 , further comprising: a reference voltage generator for generating said voltage signals to be output to said multiplexer. 
     
     
       6. The impedance matching circuit as recited in  claim 4 , wherein said negative feedback control circuit is implemented by using one of an operational amplifier, a differential amplifier, and an inverter amplifier. 
     
     
       7. An impedance matching circuit for facilitating impedance matching between the characteristic impedance of a cable and the input impedance at the input terminal of a receiver for data transmission, said impedance matching circuit comprises  comprising:
 a first transistor, including a power supply terminal, a control terminal and a load terminal, wherein said power supply terminal of said first transistor is connected to an input terminal of said receiver, and said load terminal of said first transistor is connected to the ground;  
 a resistor, wherein one terminal of said resistor is connected to a voltage source;  
 a second transistor, including a power supply terminal, a control terminal and a load terminal, wherein said power supply terminal of said second transistor is connected to the other terminal of said resistor, and said control terminal of said second transistor is connected to said control terminal of said first transistor; and  
 a negative feedback control circuit, wherein an inverting input terminal of said negative feedback control circuit receives an adjustable reference voltage, a non-inverting input terminal of said negative feedback control circuit is connected to said power supply terminal of said second transistor, and an output terminal of said negative feedback control circuit is connected to said control terminal of said second transistor;  
 wherein the equivalent resistance of said impedance matching circuit is kept equal to the resistance of the varied characteristic impedance of said cable by adjusting said reference voltage.  
 
     
     
       8. The impedance matching circuit as recited in  claim 7 , wherein said first transistor is an n-channel MOSFET. 
     
     
       9. The impedance matching circuit as recited in  claim 7 , wherein said second transistor is an n-channel MOSFET. 
     
     
       10. The impedance matching circuit as recited in  claim 7 , further comprising: a multiplexer, including a select terminal and a signal output terminal; wherein said multiplexer receives a plurality of voltage signals having different magnitudes, selects one from said plurality of voltage signals according to a select signal received by said select terminal, and then outputs said voltage signal as said reference voltage into said inverting input terminal of said negative feedback control circuit. 
     
     
       11. The impedance matching circuit as recited in  claim 10 , further comprising: a reference voltage generator for generating said voltage signals to be output to said multiplexer. 
     
     
       12. The impedance matching circuit as recited in  claim 7 , wherein said negative feedback control circuit is implemented by using one of an operational amplifier, a differential amplifier, and an inverter amplifier. 
     
     
       13. An apparatus for impedance matching at the input terminal of a receiver, comprising:
   a first controlled impedance unit utilized to provide an equivalent resistance of the input terminal according to a first control signal;        a resistor; and        an impedance control circuit, coupled to the first controlled impedance unit and to the resistor, utilized to receive an reference signal and generate the first control signal according to the reference signal and a resistance of the resistor;        wherein the reference signal is adjusted such that the equivalent resistance of the input terminal is adjusted.     
     
     
       14. The apparatus of  claim 13 , wherein the impedance control circuit comprises:
   a second controlled impedance unit, coupled to the resistor, utilized for providing an equivalent resistance of the input terminal according to the first control signal;        wherein the first controlled impedance unit is corresponding to the second controlled impedance unit.     
     
     
       15. The apparatus of  claim 14 , wherein the impedance control circuit further comprises a feedback control unit which includes an inverting input terminal, a non- inverting input terminal, and an output terminal, wherein the inverting input terminal receives the reference signal, and the non - inverting input terminal is coupled to the resistor.   
     
     
       16. The apparatus of  claim 14 , wherein the impedance control circuit further comprises a feedback control unit which is implemented by using one of an operational amplifier, a differential amplifier, and an inverter amplifier. 
     
     
       17. The apparatus of  claim 14 , wherein the first controlled impedance unit is a first transistor. 
     
     
       18. The apparatus of  claim 17 , wherein the second controlled impedance unit is a second transistor. 
     
     
       19. The apparatus of  claim 13 , wherein the impedance control circuit comprises a second controlled impedance unit, and the first controlled impedance unit is corresponding to the second controlled impedance unit. 
     
     
       20. The apparatus of  claim 21 , wherein the reference signal is adjusted such that the equivalent resistance of the input terminal is adjusted. 
     
     
       21. An apparatus for impedance matching at the input terminal of a receiver, comprising:
   a first controlled impedance unit utilized to provide an equivalent resistance of the input terminal according to a first control signal;        a resistor;        an impedance control circuit, coupled to the first controlled impedance unit and to the resistor, utilized to receive an reference signal and generate the first control signal according to the reference signal and a resistance of the resistor; and        a multiplexer, coupled to the impedance control circuit, utilized to receive a digital control signal and a plurality of reference signals, and output the reference signal according to the digital control signal.     
     
     
       22. A method for impedance matching in a receiver, comprising:
   providing a controlled impedance unit;        generating a reference signal according to a digital control signal;        generating a control signal according to the reference signal and a resistance of a resistor;        providing an equivalent resistance of the controlled impedance unit according to the control signal; and        adjusting the equivalent resistance of the controlled impedance unit when the reference signal is adjusted.     
     
     
       23. A method for impedance matching in a receiver, comprising:
   providing a controlled impedance unit;        generating a reference signal according to a digital control signal;        generating a control signal according to the reference signal and a resistance of a resistor; and        providing an equivalent resistance of the controlled impedance unit according to the control signal;        wherein the step of generating the reference signal comprises:      selecting one of a plurality of reference signals according to the digital control signal to generate the reference signal.       
     
     
       24. The method of  claim 23 , wherein the reference signal is adjusted such that the equivalent resistance of the controlled impedance unit is adjusted. 
     
     
       25. An apparatus for impedance matching at the input terminal of a receiver, comprising:
   a first controlled impedance unit utilized to provide an equivalent resistance of the input terminal according to a first control signal; and        an impedance control circuit, coupled to the first controlled impedance unit, utilized to couple to a resistor, receive an reference signal and generate the first control signal according to the reference signal and a resistance of the resistor;        wherein the reference signal is adjusted such that the equivalent resistance of the input terminal is adjusted.     
     
     
       26. The apparatus of  claim 26 , further comprising:
   a multiplexer, coupled to the impedance control circuit, utilized to receive a digital control signal and a plurality of reference signals, and output the reference signal according to the digital control signal.