Method and circuit for controlling a resistance of a field effect transistor configured to conduct a signal with a varying voltage
View Patent ↗The present invention relates to a replica network for linearizing switched capacitor circuits. A bridge circuit with a MOSFET resistor disposed in a resistor branch of the bridge circuit is provided. A noninverting terminal of an operational amplifier is connected to a first node of the bridge circuit and an inverting terminal of the operational amplifier is connected to a second node of the bridge circuit. The second node is separated from the first node by another node of the bridge circuit. An output of the operational amplifier is provided to a gate terminal of the MOSFET resistor and to the gate terminal of the MOSFET switch in a switched capacitor circuit, thereby controlling the resistance of the MOSFET switch so that it is independent of the signal voltage. In this manner, the replica network of the present invention linearizes the switched capacitor circuit. In this manner, the replica network of the present invention linearizes the switched capacitor circuit.
1. A circuit for controlling a resistance of a field effect transistor conducting a signal with a varying voltage, comprising:
a bridge circuit having a first node and a second node, the bridge circuit configured to have the signal with the varying voltage applied to the first node;
a first portion of the circuit for tracking a variation in a voltage potential between the first node and the second node; and
a second portion of the circuit for changing, in response to the variation, a voltage applied to a gate of the first field effect transistor to control the resistance of the field effect transistor;
wherein the field effect transistor is disposed outside the bridge circuit.
2. The circuit of claim 1 , further comprising:
a third portion of the circuit for determining the voltage applied to the gate of the field effect transistor from the variation in the voltage potential between the first node and the second node.
3. The circuit of claim 1 , wherein the variation in the voltage potential between the first node and the second node is proportional to a variation in a voltage potential between a source and a drain of the field effect transistor.
4. The circuit of claim 1 , wherein the variation in the voltage potential between the first node and the second node is inversely proportional to the voltage applied to the gate of the field effect transistor.
5. A method for controlling a resistance of a field effect transistor conducting a signal with a varying voltage, comprising the steps of:
(1) applying the signal with the varying voltage to a bridge circuit;
(2) tracking a variation in a voltage potential between a first node and a second node of the bridge circuit; and
(3) changing, in response to the variation, a voltage applied to a gate of the field effect transistor to control the resistance of the field effect transistor;
wherein the field effect transistor is disposed outside the bridge circuit.
6. The method of claim 5 , further comprising:
(4) determining the voltage applied to the gate of the field effect transistor from the variation in the voltage potential between the first node and the second node.
7. The method of claim 5 , wherein the variation in the voltage potential between the first node and the second node is proportional to a variation in a voltage potential between a source and a drain of the field effect transistor.
8. The method of claim 5 , wherein the variation in the voltage potential between the first node and the second node is inversely proportional to the voltage applied to the gate of the field effect transistor.
9. A method for controlling a resistance of a first field effect transistor conducting a signal with a varying voltage, comprising the steps of:
(1) applying the signal with the varying voltage to a second field effect transistor;
(2) tracking a variation in a voltage potential between a source and a drain of the second field effect transistor; and
(3) changing, in response to the variation, a first voltage applied to a gate of the first field effect transistor to control the resistance of the first field effect transistor conducting the signal with the varying voltage.
10. The method of claim 9 , further comprising:
(4) changing, in response to the variation, a second voltage applied to a gate of the second field effect transistor to control a resistance of the second field effect transistor.
11. The method of claim 10 , wherein the resistance of the second field effect transistor is proportional to the resistance of the first field effect transistor.
12. The method of claim 11 , wherein the resistance of the second field effect transistor is equal to the resistance of the first field effect transistor.
13. The method of claim 10 , wherein the second voltage is proportional to the first voltage.
14. The method of claim 13 , wherein the second voltage is equal to the first voltage.
15. A circuit for controlling a resistance of a first field effect transistor configured to conduct a signal with a varying voltage, comprising:
a second field effect transistor having a source and a drain, the second field effect transistor configured to have the signal with the varying voltage applied to one of the source and the drain;
a first portion of the circuit for tracking a variation in a voltage potential between the source and the drain of the second field effect transistor; and
a second portion of the circuit for changing, in response to the variation, a first voltage applied to a gate of the first field effect transistor to control the resistance of the first field effect transistor configured to conduct the signal with the varying voltage.
16. The circuit of claim 15 , further comprising:
a third of the circuit for changing, in response to the variation a second voltage applied to a gate of the second field effect transistor to control a resistance of the second field effect transistor.
17. The circuit of claim 16 , wherein the third portion of the circuit is the second portion of the circuit.
18. The circuit of claim 16 , wherein the resistance of the second field effect transistor is proportional to the resistance of the first field effect transistor.
19. The circuit of claim 18 , wherein the resistance of the second field effect transistor is equal to the resistance of the first field effect transistor.
20. The circuit of claim 16 , wherein the second voltage is proportional to the first voltage.
21. The circuit of claim 20 , wherein the second voltage is equal to the first voltage.