Differential amplifier offset voltage minimization independently from common mode voltage adjustment
AssigneeInternational Business Machines Corporation
InventorsMinhan Chen, Westerfield John Ficken, Louis Lu-Chen Hsu, Steven J. Zier
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Abstract
Offset voltages in differential amplifiers are minimized by controlling compensation currents through the load impedances of the amplifiers. The currents are varied while sensing the polarity of the offset voltage. When the polarity changes, the current values are latched to keep the offset voltage at a minimum.
Claims13
A offset compensation circuit for differential amplifiers having first and second load impedances and first and second differential output signal terminal means and output terminal means comprising, in combination:
- first and second adjustable current source means coupled to said differential amplifier means for supplying currents through said first and second load impedances, respectively, said first and second adjustable current source means including control input means for determining the amount of current to be supplied;
- polarity determining means coupled to said first and second output terminal means for supplying an output signal indicative of polarity of an output signal across said differential output signal terminal means;
- offset calibration means responsive to the output signal from said polarity determining means for supplying control signals to the control input means of said first and second adjustable current source means;
- and
- means in said offset calibration means for varying said control signals until said output signal from the polarity determining means indicates a change in polarity.
A method of minimizing offset voltage in a differential amplifier comprising the steps of:
- supplying a pair of currents through load impedances of the differential amplifier;
- controlling the pair of currents in opposing directions;
- sensing the polarity of the differential amplifier's output signals during a calibration phase;
- and
- latching the pair of currents at a value where the polarity of the differential amplifiers output signals changes.
A method of minimizing an offset current in differential amplifiers comprising the steps of:
- providing a pair of controllable opposing direction currents, one in each branch of a differential amplifier;
- varying the strengths of the pair of controllable opposing direction currents;
- sensing the differential amplifier's output signals' polarity;
- and
- latching the pair of controllable opposing direction currents at a value where the polarity changes.
Dependencies are inferred from the claim text.