Offset-Cancellation Circuit for Low-Noise Amplifier Accuracy
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Solution Overview
Problem
Amplifiers in devices like Successive Approximation Register Analog to Digital Converters (SAR ADCs) face performance inaccuracies due to offset voltages, and existing offset-cancellation methods introduce unwanted noise.
Innovation Solution
An offset-cancellation circuit with a first amplification stage that receives and stores an offset voltage, and a second amplification stage that delivers an offset-cancellation current based on the stored potential difference, allowing for effective cancellation while minimizing noise by decoupling the storage element and using separate gains for each stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If offset-cancellation methods are used to improve amplifier accuracy, then measurement precision is improved, but unwanted noise is introduced
Solution Approach 1:
The offset-cancellation circuit is divided into multiple independent stages: a first amplification stage that processes the offset voltage, a storage element that holds the processed offset, and a second amplification stage that generates the cancellation signal. This segmentation allows each stage to be optimized independently, improving overall accuracy while controlling noise through selective coupling and decoupling of stages.
Solution Approach 2:
The first amplification stage performs preliminary processing of the offset voltage by amplifying it with a first gain before it is stored. This preliminary action prepares the offset signal in advance, allowing the second amplification stage to work with a pre-conditioned signal, thereby improving the effectiveness of offset cancellation while enabling noise control through the intermediate storage step.
2Measurement precision
If a storage element is coupled to the amplification stage for continuous offset tracking, then offset cancellation effectiveness is improved, but noise from the storage element is continuously introduced
Solution Approach 1:
The coupling between the storage element and the amplification stages is made dynamic rather than static. The storage element can be coupled to the first amplification stage during offset measurement and then decoupled before the second amplification stage generates the cancellation signal. This dynamic coupling allows the system to track offset when needed while preventing continuous noise introduction, resolving the contradiction between effectiveness and noise.
Data Source
AI summary
An offset-cancellation circuit having a first amplification stage with a gain of the first amplification stage and configured to receive an offset voltage of a first amplifier. A storage element is configured to be coupled to and decoupled from the first amplification stage and configured to store a potential difference output by the first amplification stage. The potential difference is determined by the offset voltage of the first amplifier and the gain of the first amplification stage. A second amplification stage is coupled to the storage element and configured to receive the potential difference from the storage element when the storage element is decoupled from the first amplification stage and configured to deliver an offset-cancellation current. The offset-cancellation current is determined by the potential difference and a gain of the second amplification stage.