Common-mode feedback bias generator for operational amplifiers
AssigneeTexas Instruments Incorporated
InventorsJohn W. Fattaruso, Venugopal Gopinathan
Life of this patent
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Abstract
A common-mode feedback circuit comprises a reference generator (12) for generating a signal corresponding to a desired common-mode operating point connected to a common-mode bias circuit (14) for generating a second signal corresponding to the common-mode operating point of the outputs (V.sub.out.sup.+, V.sub.out.sup.-) of the fully differential operational amplifier. In the preferred embodiment, the common-mode bias circuit (14) includes a sensing circuit (58) comprising two MOS transistors (60, 62) having sources and drains connected together. The MOS transistors (60, 62) operate in the ohmic region to provide a variable load responsive to the output signals (V.sub.out.sup.+, V.sub.out.sup.-) connected to their gates.
Claims14
A common-mode feedback circuit for use in a fully differential operation amplifier comprising:
- circuitry to generate a first signal corresponding to a desired common-mode voltage;
- circuitry to generate a second signal corresponding to the common-mode operating point of the output of the fully differential operational amplifier;
- and
- circuitry to adjust the common-mode operating point of the output of the fully differential operational amplifier based on a comparison of said first and second signals,
- wherein said circuitry to generate a second signal comprises circuitry to provide a variable current responsive to the common-mode operating point of the output of the fully differential operational amplifier.
A common-mode feedback circuit for use in a fully differential operational amplifier comprising:
- circuitry to generate a first signal corresponding to a desired common-mode voltage;
- circuitry to generate a second signal corresponding to the common-mode operating point of the output of the fully differential operational amplifier;
- and
- circuitry to adjust the common-mode operating point of the output of the fully differential operational amplifier based on a comparison of said first and second signals,
- wherein said circuitry to generate a second signal comprises circuitry to provide a variable resistance responsive to the common-mode operating point of the output of the fully differential operational amplifier.
An operational amplifier comprising:
- differential amplifier circuitry including input nodes for receiving a differential input and output circuitry connected to said input nodes for providing a differential output signal to first and second output nodes responsive to said differential input;
- detection circuitry connected to said differential amplifier circuitry for producing a first signal corresponding to the common-mode operating point of said differential output signal,
- said detection circuitry comprising a variable conductance element responsive to the common-mode operating point of said output circuitry;
- reference circuitry connected to said detection circuitry for providing a second signal corresponding to a desired common-mode operating point having a well known relationship with said first signal;
- and
- compare circuitry for providing a third signal to said output circuitry for indicating a mismatch between said first and second signals.
An operational amplifier comprising:
- differential amplifier circuitry including input nodes for receiving a differential input and output circuitry connected to said input nodes for providing a differential output signal to first and second output nodes responsive to said differential input;
- detection circuitry connected to said differential amplifier circuitry for producing a first signal corresponding to the common-mode operating point of said differential output signal;
- reference circuitry connected to said detection circuitry providing a second signal corresponding to a desired common-mode operating point having a known relationship with said first signal;
- and
- compare circuitry for providing a third signal to said output circuitry for indicating a mismatch between said first and second signals,
- said differential amplifier circuitry including load circuitry comprising a pair of MOS transistors having respective first source/drains connected to a predetermined voltage, respective second source/drain connected to said output nodes and gates connected to said compare circuitry.
A method for providing common-mode feedback for use in a fully differential operational amplifier, comprising the steps of:
- generating a first signal corresponding to a desired common-mode voltage;
- generating a second signal corresponding to the common-mode operating point of the output of the fully differential operational amplifier.
- said step of generating a second signal comprises the step of generating a variable current responsive to the common-mode operating point of the output of the fully differential operational amplifier;
- and
- adjusting the common-mode operating point of the output of the fully differential operational amplifier based on a comparison of said first and second signals.
A method for providing common-mode feedback for use in a fully differential operational amplifier, comprising the steps of:
- generating a first signal corresponding to a desired common-mode voltage;
- generating a second signal corresponding to the common-mode operating point of the output of the fully differential operational amplifier,
- said step of generating a second signal comprising the step of varying a resistance responsive to the common-mode operating point of the output of the fully differential operational amplifier;
- and
- adjusting the common-mode operating point of the output of the fully differential operational amplifier based on a comparison of said first and second signals.
A method of providing common-mode feedback in a fully differential amplifier comprising the steps of:
- receiving a differential input;
- generating a differential output signal responsive to said differential input;
- generating a first signal corresponding to the common-mode operating point of the differential output signal,
- said step of generating a first signal comprising the step of generating a first signal by varying a conductance element responsive to the common-mode operating point of the output circuitry;
- generating second signal corresponding to a desired common-mode operating point having a known relationship with said first signal;
- and
- adjusting the common-mode operating point of a differential output signal based on said first and second signals.
Dependencies are inferred from the claim text.