Amplifier Offset-Cancellation Circuit With Stored Offset Sampling
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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, which existing noise cancellation methods often introduce unwanted noise, limiting their effectiveness.
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 precise cancellation while minimizing noise introduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If offset cancellation is performed using conventional methods, then amplifier offset is reduced, but unwanted noise is introduced
Solution Approach 1:
The offset cancellation circuit is divided into multiple stages: a first amplification stage that processes the offset voltage, a storage element that holds the amplified offset, and a second amplification stage that generates the cancellation signal. This segmentation allows each stage to be optimized independently, achieving offset cancellation while controlling noise propagation through the system.
Solution Approach 2:
The storage element captures and holds the amplified offset voltage from the first amplification stage before it is used by the second amplification stage. This preliminary action allows the offset to be measured and stored under controlled conditions, then applied for cancellation without introducing additional noise during the transfer process.
2Device complexity
If a single amplification stage is used for offset cancellation, then circuit complexity is reduced, but noise cancellation effectiveness is limited
Solution Approach 1:
The circuit uses two separate amplification stages with distinct functions: the first stage amplifies the offset voltage for storage, while the second stage uses the stored offset to generate the cancellation signal. This segmentation enables each amplifier to be optimized for its specific task, improving overall noise cancellation effectiveness while maintaining manageable circuit complexity.
Solution Approach 2:
The storage element acts as an intermediary between the two amplification stages, holding the amplified offset voltage and isolating the first stage from the second stage's noise-sensitive operations. This intermediary structure allows precise offset capture without propagating noise from the second stage back to the first.
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.