Pipeline ADC Capacitor Partitioning for Amplifier Offset Cancellation
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Solution Overview
Problem
Pipeline ADCs face accuracy issues due to amplifier offset voltage accumulation, which affects the input-output transfer curve and is critical in applications requiring absolute conversion accuracy.
Innovation Solution
The solution involves partitioning capacitors in a specific ratio to form smaller and larger capacitors, where the smaller capacitors are used for offset compensation, allowing the amplifier's offset to be effectively canceled out, thereby maintaining the same capacitive load and noise properties as the standard 1.5 bits-per-stage architecture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If amplifier sharing between adjacent stages is used to reduce power consumption, then power consumption is reduced, but amplifier offset voltage accumulates and affects conversion accuracy
Solution Approach 1:
The feedback capacitor C1 is segmented into two separate capacitors: a main feedback capacitor (C1b) and a compensation capacitor (C1a). This segmentation allows the compensation capacitor to specifically target and cancel the amplifier offset voltage while the main feedback capacitor maintains the primary feedback function, thereby resolving the accuracy degradation caused by amplifier sharing.
Solution Approach 2:
The compensation capacitor C1a acts as an intermediary element that mediates between the amplifier offset voltage and the feedback signal. By introducing this intermediate compensation path, the offset voltage can be canceled independently without affecting the main feedback loop, thus maintaining conversion accuracy while enabling amplifier sharing.
2Measurement precision
If standard 1.5 bits-per-stage architecture is used, then conversion accuracy is maintained, but power consumption increases due to dedicated amplifiers per stage
Solution Approach 1:
The feedback capacitor structure is designed with multi-functionality: the main feedback capacitor C1b provides the primary feedback function for signal conversion, while the compensation capacitor C1a provides offset cancellation. This universal capacitor design enables a single amplifier to serve multiple stages while maintaining both accuracy and enabling power reduction through amplifier sharing.
3Device complexity
If amplifier offset is not compensated, then device complexity is reduced, but input-output transfer curve accuracy deteriorates
Solution Approach 1:
The offset compensation function is merged with the existing feedback capacitor structure rather than being implemented as a separate compensation circuit. By combining the compensation capacitor C1a with the main feedback capacitor C1b in parallel, the patent achieves offset compensation without adding significant circuit complexity, thus resolving the trade-off between complexity and accuracy.
Data Source
AI summary
An apparatus, method and system for offset compensation in a pipeline analog-to-digital converter. A group of capacitors includes one or more sampling capacitors and one or more feedback capacitors, wherein an input to the pipeline analog-to-digital converter circuit is connected to group of capacitors. An amplifier includes a non-inverting input terminal connected to a ground and an inverting input connected to the group of capacitors. The sampling and feedback capacitors are both partitioned in the same ratio to form partitioned capacitors such that a smaller of the partitioned capacitors is employed for offset compensation with respect to the pipeline analog-to-digital converter.