Common mode stabilizing circuit and method
AssigneeHarris Corporation
InventorRobert S. Cargill
Life of this patent
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Abstract
A circuit and method for stabilizing a common mode voltage in a differential circuit provides a desired common mode voltage V.sub.cm to control terminals of two transistors which provide the variable resistance for setting the common mode voltage. V.sub.cm is sampled between load resistors R.sub.L connecting operating terminals of the two transistors and applied directly to their control terminals. A known common mode current I.sub.cm is accepted by each transistor, leaving a differential current I.sub.d to flow through load resistors R.sub.L. The circuit and method find application in a variety of uses, including transconductance and transresistance amplifiers and automatic gain control circuits.
Claims20
A circuit for stabilizing a common mode voltage at a reference voltage, the circuit comprising:
- two transistors with their control terminals connected;
- two series-connected load resistors connecting first operating terminals of said two transistors, second operating terminals of said two transistors being connected to a voltage level;
- and
- a connection for providing the reference voltage from between said two load resistors directly to said control terminals for controlling operation of said two transistors;
- wherein each of said first operating terminals is for sensing an input current which varies from a known common mode current and for providing an output voltage which varies from a stable common mode voltage which is the reference voltage.
A circuit with two transistors for receiving input currents at first operating terminals, the input currents including a known common mode current, the circuit for providing a stable common mode voltage and comprising:
- two series-connected load resistors connecting the first operating terminals of the two transistors;
- and
- a connection from between said two load resistors directly to control terminals of the two transistors,
- whereby the average of the output voltages from the first operating terminals is the stable common mode voltage.
A method of stabilizing a common mode voltage at a reference voltage comprising the steps of:
- (a) receiving input currents at first operating terminals of two transistors, the input currents including a known common mode current;
- (b) contacting the first operating terminals of the two transistors to each other across two series-connected load resistors;
- (c) sensing a voltage between the two series-connected load resistors and providing the sensed voltage directly to control terminals of the two transistors,
- whereby the average of the output voltages from the first operating terminals is the stable common mode voltage.
A method of stabilizing a common mode voltage of an input signal comprising the steps of providing the desired common mode voltage directly to control terminals of two transistors which provide variable resistances for setting the common mode voltage, and providing output voltages from first operating terminals of the two transistors, the output voltages having the desired common mode voltage.
Dependencies are inferred from the claim text.