Cascaded Amplifier Offset Cancellation Under Saturation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Multi-stage amplifiers face issues with offset cancellation, particularly when processing small signals or low data rates, leading to saturation and increased input-referred offset due to mismatch and noise, which conventional offset cancellation methods struggle to address effectively.
Innovation Solution
A cascaded amplifier configuration with feedback loops from each stage to the previous stage, utilizing multiple offset cancellation amplifiers connected between each stage's output and input, and a single offset cancellation amplifier in a feedback loop between the first and last stages, reduces the impact of mismatch and saturation by distributing feedback and maintaining gain across a wider input range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the gain of the offset cancellation amplifier is increased to reduce input-referred offset, then the offset cancellation performance is improved, but the amplifier stages saturate more easily and the circuit consumes more power
Solution Approach 1:
The patent divides the offset cancellation function into multiple independent feedback loops, with each loop handling offset cancellation for a specific amplifier stage. This segmentation allows each feedback loop to operate with moderate gain without causing saturation in subsequent stages, while collectively achieving excellent overall offset cancellation performance. The multiple feedback amplifiers work in parallel to cancel offsets from different stages independently.
2Manufacturing precision
If the size of the offset cancellation amplifier is increased to reduce mismatch, then the mismatch error is reduced by approximately 50%, but the area and power consumption increase significantly
Solution Approach 1:
The patent implements multiple feedback amplifiers with moderate sizing rather than one large high-precision amplifier. By distributing the offset cancellation function across multiple smaller amplifiers, each handling a specific stage, the overall mismatch performance improves while individual amplifier sizes remain compact, reducing total area consumption.
Solution Approach 2:
The patent combines multiple feedback loops into a unified offset cancellation system where each loop contributes to the overall offset reduction. The multiple feedback amplifiers work together synergistically to achieve high precision offset cancellation that would require a much larger single amplifier, thereby reducing total circuit area while maintaining manufacturing precision.
3Device complexity
If a single offset cancellation loop is used from the last stage to the first stage, then the device complexity is reduced, but the offset cancellation effectiveness decreases when input data rate is low
Solution Approach 1:
The patent segments the offset cancellation function into multiple independent feedback loops, each monitoring and correcting offset at a specific amplifier stage. This segmentation provides better offset cancellation effectiveness across different input data rates compared to a single loop, as each stage's offset can be corrected independently without being affected by saturation in other stages.
4Measurement precision
If the gain of the main amplifier stages is increased to process small signals, then the signal processing capability is improved, but the offset and noise become more significant relative to the signal
Solution Approach 1:
The patent implements multiple feedback loops that continuously monitor the output of each amplifier stage and feed correction signals back to the input of the same or previous stages. This feedback mechanism dynamically cancels offset and reduces noise impact, enabling the main amplifier stages to operate with high gain for small signal processing while maintaining low offset and noise levels through active correction.
Data Source
AI summary
An offset cancellation circuit and method are provided where successive stages of cascaded amplifiers are operated in a saturated state. Biasing is provided, by a feedback amplifier, connected in a feedback loop for each cascaded amplifier, so as to be responsive, in a non-saturated state, to the input of an associated amplifier stage operating in the saturated state.