Adaptive operational amplifier offset voltage trimming system
AssigneeAnalog Devices, Inc.
InventorMarcellus R. Chen
Life of this patent
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Abstract
A system for adaptively trimming the input offset voltage of an op amp employing an input stage with complementary differential pairs provides accurate VDos trimming over the amplifier's entire common-mode input range, by providing an “adaptive” trim signal that varies with the current conducted by one of the complementary pairs. Switching circuitry insures that only one differential pair is active at a time, except in a transition region in which both pairs are partially conducting. The use of an adaptive trim signal enables Vos to be kept low over the full range of common-mode input voltages, including in the amplifier's transition region.
Claims16
An adaptive operational amplifier offset voltage trimming system, comprising:
- an operational amplifier comprising:
- an input stage comprising complementary differential pairs connected to receive a differential input and biased to produce respective differential output currents in response,
- an output stage arranged to receive said differential output currents and to produce an output in response, said output stage including at least one trim input and arranged to vary said output in response to one or more trim signals applied to said at least one trim input,
- a switching circuit connected to said complementary differential pairs and arranged to activate one or the other of said pairs depending on the common-mode input voltage presented at said differential input, and
- trim circuitry arranged to track the current conducted by at least one of said complementary differential pairs and to provide an adaptive trim signal which varies with said tracked current to said at least one trim input to reduce said operational amplifier's input offset voltage,
- wherein said operational amplifier is powered by first and second supply voltages and has a common-mode input range which includes said first and said second supply voltages, said adaptive trim signal enabling said amplifier's input offset voltage to be reduced over its entire common mode input range.
An adaptive operational amplifier offset voltage trimming system, comprising:
- an operational amplifier powered by first and second supply voltages and having a common-mode input range which includes said first and said second supply voltages, said amplifier including:
- a first differential pair connected to receive a differential input and to produce a first differential current in response, said first pair arranged to conduct for common-mode voltages that are in a first portion of said common-mode input range,
- a second differential pair complementary to said first pair and connected to receive said differential input and to produce a second differential current in response, said second pair arranged to conduct for common-mode voltages that are outside said first portion of said input range,
- a switching circuit coupled to said first and second differential pairs and arranged to turn off said first pair and to activate said second pair when the common-mode input voltage presented at said differential input is outside of said first portion of said input range, and
- an output stage arranged to receive said differential output currents and to produce an output in response, said output stage including at least one trim input and arranged to vary said output in response one or more trim signals applied to said at least one trim input, and
- trim circuitry, comprising:
- a first trim circuit arranged to provide a first trim signal to said at least one trim input which is about constant over said common-mode input range, and
- a second trim circuit arranged to track the current in said second pair and to provide an adaptive trim signal which varies with said tracked current to said at least one trim input to reduce said operational amplifier's input offset voltage over its entire common mode input range.
Dependencies are inferred from the claim text.