US 6,583,660 B2 · Active auto zero circuit for time continuous open loop amplifiers

Abstract

An active offset cancellation circuit for an open loop differential amplifier is disclosed. The amplifier is operated on a two-phase clock where the normal operation occurs on the first phase and offset detection and cancellation occurs on the second phase. On the second phase, the offset cancellation circuit measures the offset created by the amplifier when both differential inputs are connected to a common source. The circuit then adjusts a bias current and stores this adjustment to cancel offset during the operational phase of the amplifier. During the operational phase, the first phase of the clock, the stored adjustment is used to bias the current in one of the two input stages of the amplifier, canceling any offset imparted by the amplifier circuitry. One each clock cycle, any additional offset is similarly detected and canceled.

Claims10

Dependent claims

A differential amplifier comprising:

a first input stage operative to receive a first input signal of a differential signal pair;
a second input stage operative to receive a second input signal of said differential signal pair;
an output stage operative to produce first and second differential output signals equal to the amplification of the difference between the first signal and the second signal;
and
an offset cancellation circuit operative to actively cancel offset voltage in said first and second differential output signals added by said differential amplifier wherein said differential amplifier is responsive to a two-phase clock, wherein said first input stage is further operative to receive said first input signal on a first phase of said two-phase clock and receive a common signal on a second phase of said two-phase clock, said second input stage is further operative to receive said second input signal on said first phase and receive said common signal on said second phase and further wherein said offset cancellation circuit is further operative to compute an adjusted bias current on said second phase and said offset cancellation circuit is further operative apply said adjusted bias current on said first phase to cancel said offset voltage.

2 more elements

Dependencies are inferred from the claim text.

Active auto zero circuit for time continuous open loop amplifiers

Life of this patent

Active auto zero circuit for time continuous open loop amplifiers

Life of this patent

Abstract

Claims10