SAR ADC Latch Alternation for Faster Precise Conversion
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Solution Overview
Problem
Successive approximation register (SAR) analog-digital converters face a trade-off between speed, power efficiency, and conversion precision, with reset time being a critical limiting factor that affects overall performance.
Innovation Solution
The proposed method involves operating at least two decision latches in an alternating fashion, allowing one latch to perform a decision step while the other resets, thereby reducing the overall power consumption and latency, and optimizing the design of decision latches to minimize area penalty and calibration complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the reset time of the decision latch is reduced to increase conversion speed, then conversion precision deteriorates due to increased conversion offset
Solution Approach 1:
The patent divides the decision latch function into two separate latches operating in alternating fashion. One latch (first decision latch) is dedicated to evaluation while the other (second decision latch) handles resetting. This segmentation allows simultaneous execution of evaluation and reset operations, eliminating the sequential bottleneck without compromising evaluation accuracy.
Solution Approach 2:
The patent implements continuous useful action by having one latch evaluate while the other resets, and vice versa in the next cycle. This alternating operation ensures that evaluation actions continue without interruption while reset operations proceed in parallel, maximizing throughput without sacrificing precision.
2Speed
If multiple decision latches are used to increase conversion speed, then device complexity and area increase
Solution Approach 1:
The patent segments the decision latch functionality into exactly two specialized latches: one for evaluation and one for resetting. This minimal segmentation achieves parallel operation benefits while avoiding the complexity of using more latches. The segmented approach reduces calibration complexity compared to using multiple latches for each bit position.
Solution Approach 2:
Each latch in the patent performs multiple functions across different time cycles. The first decision latch alternates between evaluation and reset roles, and the second latch does the same. This multi-functionality reduces the total number of latches needed compared to dedicated latches for each function, simplifying the overall device.
3Measurement precision
If the latch reset time is extended to improve conversion precision, then conversion speed decreases due to increased latch cycle period
Solution Approach 1:
The patent segments the latch operations so that reset time is distributed across alternating cycles rather than concentrated in single cycles. While one latch undergoes extended reset for precision, the other latch simultaneously performs evaluation, effectively hiding the reset time penalty and maintaining high conversion speed.
Solution Approach 2:
The patent maintains continuous useful action by ensuring that while one latch is resetting, the other is evaluating. This continuity prevents idle time in the conversion pipeline, allowing the system to achieve both precise resetting and fast conversion by overlapping these operations in time.
Data Source
AI summary
A method and apparatus for operating an analog-digital converter for converting an input signal into a multibit output in one conversion cycle. The method includes loading a capacitor array by applying a given input signal potential, evaluating a sampling potential provided by the capacitor array in a number of consecutive decision steps performed by at least two decision latches and changing the sampling potential by switching the capacitor array for each decision step based on a result of the step of evaluating the sampling potential, where the step of evaluating at least one of the decision latches performs the evaluating for two decision steps.