Negative feedback CMOS differential amplifier operating in common mode
AssigneeSGS-Thomson Microelectronics S.A.
InventorThierry Fensch
Life of this patent
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Abstract
In a CMOS amplifier having a differential input and differential output, the input stage includes two legs, each of which includes an input transistor. A common mode negative feedback stage includes a load connected to the high supply voltage, a first transistor connected between the load and a common terminal of the input transistors. The first transistor is biased to the desired common mode voltage. A second transistor is connected between the load and the low supply voltage, and has a gate connected to a voltage corresponding to the mean voltage of the output stage. An additional transistor is disposed in parallel with each input transistor. Each additional transistor has its gate connected to the desired common mode voltage.
Claims22
A differential amplifier, comprising:
- a differential input stage having two circuit legs, each leg including an input device for receiving an input voltage and controlling a current through the device in response to the input voltage;
- a biasing circuit that maintains a flow of current through the circuit legs of the input stage when the input devices become non-conductive.
A differential amplifier, comprising:
- first and second circuit branches having first and second currents, respectively, each branch including an input transistor for receiving an input voltage and controlling a transistor current in response to the input voltage, the first and second circuit branches being joined together at a common junction;
- a third circuit branch supplying a third current to the common junction, the first, second, and third currents summing together to form a substantially constant current;
- a bias circuit connected in parallel with the input transistors, that maintains the first and second currents above a predetermined threshold current when the transistor currents fall below the predetermined threshold.
A differential amplifier, comprising:
- a differential input stage having two circuit legs, each leg including a device for receiving an input voltage and controlling a current through the device in response to the input voltage;
- bias means for maintaining a flow of current through the circuit legs of the input stage when the input devices become non-conductive.
A method for maintaining a flow of current in an input stage of a differential amplifier having a pair of input devices, comprising the steps of:
- generating a threshold signal indicative of an input voltage to the differential amplifier for which the pair of input devices are conductive;
- shunting current around the input devices when both input voltages cross the threshold signal in a first direction, and
- substantially terminating the shunting of current when at least one of the input voltages crosses the threshold signal in a second direction opposite the first direction.
Dependencies are inferred from the claim text.