High linearity, low power voltage controlled resistor

Abstract

A number of voltage-controlled resistance cells, each formed by a transistor with a biasing capacitor connected between the gate and source and an associated controller coupled to the capacitor to maintain a steady charge on the biasing capacitor and keep the gate-source voltage at a control voltage corresponding to a desired resistance, are employed to form a voltage-controlled resistance structure. The gate voltage applied to each transistor is able to “float” together with the source voltage in order to keep the gate-source voltage constant, and the resistance structure exhibits improved voltage-dependent resistance linearity together with a larger range of biasing while lowering needed refresh frequencies to avoid noise injection.

1. For use in an integrated circuit, a voltage controlled resistance cell for provided a voltage-controlled variable resistance having improved voltage-dependent resistance linearity comprising:
 a transistor providing a voltage-controlled resistance between a drain and a source of the transistor in response to a control voltage applied across a gate and the source of the transistor;    a biasing capacitor connected between the gate and the source, the biasing capacitor maintaining a gate-source voltage on the voltage-controlled resistance transistor to produce a corresponding resistance between the drain and the source of the voltage-controlled resistance transistor; and    a controller coupled to the capacitor and maintaining a steady charge on the capacitor.    
     
     
       2. The  For use in an integrated circuit, a voltage controlled resistance cell as set forth in  claim 1   for providing a voltage- controlled variable resistance having improved voltage - dependent resistance linearity, the voltage - controlled resistance cell comprising:  
   a transistor providing a voltage - controlled resistance between a drain and a source of the transistor in response to a control voltage applied across a gate and the source of the transistor;    
   a biasing capacitor connected between the gate and the source, the biasing capacitor maintaining a gate - source voltage on the voltage - controlled resistance transistor to produce a corresponding resistance between the drain and the source of the voltage - controlled resistance transistor; and    
   a controller coupled to the biasing capacitor and maintaining a steady charge on the capacitor,  wherein the controller further comprises:  
 a regulating capacitor capable of being selectively coupled in parallel with the biasing capacitor, the regulating capacitor receiving the control voltage and passing the control voltage to the biasing capacitor when coupled to the biasing capacitor.  
 
     
     
       3. The voltage controlled resistance cell as set forth in  claim 2  wherein the controller further comprises:
 a first transistor coupling a first terminal of the regulating capacitor to a first terminal of the biasing capacitor; and  
 a second transistor coupling a second terminal of the regulating capacitor to a second terminal of the biasing capacitor,  
 wherein the regulating capacitor is coupled to the biasing capacitor when the first and second transistors are on.  
 
     
     
       4. The voltage controlled resistance cell as set forth in  claim 3  wherein the controller further comprises:
 a third transistor coupling the first terminal of the regulating capacitor to a control voltage input; and  
 a fourth transistor coupling the second terminal of the regulating capacitor to a ground voltage.  
 
     
     
       5. The voltage controlled resistance cell as set forth in claim  1    2  wherein the controller sets the gate-source voltage on the voltage-controlled resistance transistor to the control voltage. 
     
     
       6. The voltage controlled resistance cell as set forth in claim  1    2  wherein the voltage-controlled resistance transistor forms a portion of a voltage controlled resistance structure when the drain of the voltage-controlled resistance transistor is connected to a source of a voltage-controlled resistance transistor within another resistance cell. 
     
     
       7. A voltage controlled resistance structure comprising:
 a plurality of voltage controlled resistance cells connected in series for provided a voltage-controlled variable resistance having improved voltage-dependent resistance linearity, each resistance cell comprising: 
 a transistor providing a voltage-controlled resistance between a drain and a source of the transistor in response to a control voltage applied across a gate and the source of the transistor;  
 a biasing capacitor connected between the gate and the source, the biasing capacitor maintaining a gate-source voltage on the voltage-controlled resistance transistor to produce a corresponding resistance between the drain and the source of the voltage-controlled resistance transistor; and  
 a controller coupled to the capacitor and maintaining a steady charge on the capacitor.  
   
     
     
       8. The  A voltage controlled resistance structure as set forth in  claim 7   comprising:
   a plurality of voltage controlled resistance cells connected in series for provided a voltage - controlled variable resistance having improved voltage - dependent resistance linearity, each resistance cell comprising:    
   a transistor providing a voltage - controlled resistance between a drain and a source of the transistor in response to a control voltage applied across a gate and the source of the transistor;    
   a biasing capacitor connected between the gate and the source, the biasing capacitor maintaining a gate - source voltage on the voltage - controlled resistance transistor to produce a corresponding resistance between the drain and the source of the voltage - controlled resistance transistor; and    
   a controller coupled to the biasing capacitor and maintaining a steady charge on the capacitor,  wherein the controller for each resistance cell further comprises:  
 a regulating capacitor capable of being selectively coupled in parallel with the biasing capacitor, the regulating capacitor receiving the control voltage and passing the control voltage to the biasing capacitor when coupled to the biasing capacitor.  
 
     
     
       9. The voltage controlled resistance structure as set forth in  claim 8  wherein the controller for each resistance cell further comprises:
 a first transistor coupling a first terminal of the regulating capacitor to a first terminal of the biasing capacitor; and  
 a second transistor coupling a second terminal of the regulating capacitor to a second terminal of the biasing capacitor,  
 wherein the regulating capacitor is coupled to the biasing capacitor when the first and second transistors are on.  
 
     
     
       10. The voltage controlled resistance structure as set forth in  claim 9  wherein the controller for each resistance cell further comprises:
 a third transistor coupling the first terminal of the regulating capacitor to a control voltage input ; and  
 a fourth transistor coupling the second terminal of the regulating capacitor to a ground voltage.  
 
     
     
       11. The voltage controlled resistance structure as set forth in  claim 10  wherein the controller for each resistance cell sets the gate-source voltage on the voltage-controlled resistance transistor within the corresponding resistance cell to the control voltage. 
     
     
       12. The voltage controlled resistance structure as set forth in  claim 10  wherein the controller for each resistance cell further comprises:
 a first input for receiving the control voltage;  
 a second input for receiving a first control signal controlling the first transistor;  
 a third input for receiving a second control signal controlling the second transistor; and  
 a fourth input for receiving a third control signal controlling the third and fourth transistors.  
 
     
     
       13. For use in an integrated circuit, a method of controlling a voltage controlled resistance comprising:
 applying a control voltage across a gate and a source of at least one voltage-controlled resistance transistor and across at least one biasing capacitor connected between the gate and the source, the at least one voltage-controlled resistance transistor producing a resistance corresponding to the control voltage between a drain and the source of the at least one voltage-controlled resistance transistor; and  
 maintaining a steady charge on the at least one biasing capacitor by selectively coupling a regulating capacitor to the at least one biasing capacitor, wherein the regulating capacitor is capable of being selectively coupled to the control voltage.  
 
     
     
       14. The method as set forth in  claim 13  wherein the step of applying a control voltage across a gate and a source of at least one voltage-controlled resistance transistor and across at least one biasing capacitor connected between the gate and the source further comprises:
 applying the control voltage across a gate and a source of each of a plurality of voltage-controlled resistance transistors connected in series and across a plurality of biasing capacitors each connected between the gate and source of one of the plurality of voltage-controlled resistance transistors.  
 
     
     
       15. The method as set forth in  claim 14  wherein the step of maintaining a steady charge on the at least one biasing capacitor further comprises:
 maintaining a steady charge on each of the plurality of biasing capacitors.  
 
     
     
       16. The method as set forth in  claim 13  wherein the step of maintaining a steady charge on the at least one biasing capacitor further comprises:
 selectively coupling a regulating capacitor to the at least one biasing capacitor, wherein the regulating capacitor is capable of being selectively coupled to the control voltage.    
     
     
       17. The method as set forth in claim  16    13  further comprising:
 selectively coupling one terminal of the regulating capacitor to the control voltage and a second terminal of the regulating capacitor to a ground voltage.  
 
     
     
       18. The method as set forth in  claim 17  further comprising:
 disconnecting the regulating capacitor from the biasing capacitor before coupling the regulating capacitor to the control voltage and disconnecting the regulating capacitor from the control voltage before recoupling the regulating capacitor to the biasing capacitor.  
 
     
     
       19. The method as set forth in  claim 17  further comprising:
 periodically connecting the regulating capacitor to the control voltage and to the biasing capacitor in sequence.  
 
     
     
       20. The method as set forth in  claim 17  further comprising:
 driving a common set of control signals to periodically refresh or alter the control voltage applied to across the gate and source of each of the plurality of voltage-controlled resistance transistors.  
 
     
     
       21. For use in an integrated circuit, a voltage controlled resistance cell for providing a voltage- controlled variable resistance having improved voltage - dependent resistance linearity, the voltage controlled resistance cell comprising:      a transistor providing a voltage - controlled resistance between a drain and a source of the transistor in response to a control voltage applied across a gate and the source of the transistor;        a biasing capacitor connected between the gate and the source, the biasing capacitor providing a gate - source voltage on the voltage - controlled resistance transistor to produce a corresponding resistance between the drain and the source of the voltage - controlled resistance transistor; and        a controller coupled to the biasing capacitor to selectively charge the biasing capacitor and allow the voltage at the gate of the transistor to follow the voltage at the source of the transistor when there is a variation in voltage at the source and thereby maintain the gate - source voltage constant,        wherein the transistor provides a voltage - controlled resistance to a circuit connected across the drain and the source of the transistor, and        wherein the controller is connected only to the gate and the source of the transistor, and not to the drain of the transistor.      
     
     
       22. A voltage controlled resistance structure comprising:
   a plurality of voltage - controlled resistance cells connected in series for providing a voltage - controlled variable resistance having improved voltage - dependent resistance linearity, each resistance cell comprising:      a transistor providing a voltage - controlled resistance between a drain and a source of the transistor in response to a control voltage applied across a gate and the source of the transistor;        a biasing capacitor connected between the gate and the source, the biasing capacitor providing a gate - source voltage on the voltage - controlled resistance transistor to produce a corresponding resistance between the drain and the source of the voltage - controlled resistance transistor; and        a controller coupled to the capacitor and charging the capacitor and allow the voltage at the gate of the transistor to follow the voltage at the source of the transistor when there is a variation in voltage at the source and thereby maintain the gate - source voltage constant,        wherein each transistor provides a voltage - controlled resistance to a circuit connected across the series of voltage controlled resistance cells, and        wherein each controller is connected only to the gate and the source of the respective transistor within the same voltage - controlled resistance cell, and not to the drain of the respective transistor.        
     
     
       23. For use in an integrated circuit, a method of controlling a voltage controlled resistance comprising:
   applying a control voltage across a gate and a source of at least one voltage - controlled resistance transistor and across at least one biasing capacitor connected between the gate and the source, the at least one voltage - controlled resistance transistor producing a resistance corresponding to the control voltage between a drain and the source of the at least one voltage - controlled resistance transistor, wherein the transistor provides a voltage - controlled resistance to a circuit connected across the drain and the source of the transistor; and        using a controller connected only to the gate and the source of the transistor, and not to the drain of the transistor, charging the at least one biasing capacitor and allowing the voltage at the gate of the transistor to follow the voltage at the source of the transistor when there is a variation in voltage at the source and thereby maintaining the gate - source voltage constant.