Multi-Stage SAR ADC Auto-Zeroing for Charge Injection Capture
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current multi-stage SAR ADC circuits struggle to accurately capture switch charge injections and comparator kickback effects, leading to higher offset voltages and inadequate support for high-precision and high-performance use cases.
Innovation Solution
The implementation of a multi-stage SAR ADC circuit with an enhanced Auto Zero (AZ) phase that measures charge injection from both internal and external sources within the sub-ADC, and repeats switch transitions from the sample and conversion phases to improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional Auto Zero phase is used in multi-stage SAR ADC circuits, then the circuit operation is simple, but the offset voltage is high due to inability to accurately capture switch charge injections and comparator kickback effects
Solution Approach 1:
The Auto Zero phase is divided into multiple sequential configurations (third through sixth configurations) that separately capture different error sources: switch charge injections during sampling and comparator kickback effects during conversion. This segmentation allows precise measurement of each error component independently, achieving high offset voltage accuracy without requiring complex simultaneous measurement circuits.
Solution Approach 2:
The circuit performs preliminary error capture by repeating switch transitions from the sample and conversion phases during the Auto Zero phase. By pre-capturing charge injection effects and kickback effects in dedicated configurations before the final AZ decision, the circuit prepares accurate error measurements that are then used to correct the main conversion, improving offset voltage accuracy without adding complexity to the primary conversion path.
2Measurement precision
If switch transitions are repeated during Auto Zero phase, then charge injection and kickback effects are captured accurately, but the phase duration increases
Solution Approach 1:
The Auto Zero phase employs periodic switching actions where switches are configured to repeat the exact same transition patterns as the sample and conversion phases. By using periodic, repetitive switch configurations (third configuration mirroring sampling phase, fourth configuration mirroring conversion phase), the circuit efficiently captures charge injection and kickback effects through pattern repetition rather than requiring extended measurement periods, thus maintaining precision while limiting time overhead.
3Measurement precision
If multiple switch configurations are used to capture different error sources, then measurement accuracy improves, but the control logic becomes more complex
Solution Approach 1:
The Auto Zero phase configurations are direct copies of the sample and conversion phase configurations. The third configuration copies the sampling phase switch states, the fourth configuration copies the conversion phase switch states, and subsequent configurations copy these patterns to capture corresponding error sources. This copying approach ensures measurement accuracy by replicating exact operational conditions, while the control complexity is managed by reusing existing phase control logic rather than designing entirely new control sequences.
Data Source
AI summary
An example apparatus includes: controller circuitry configured to: provide switch signals to capacitive digital to analog converter (C-DAC) circuitry, the C-DAC circuitry including switches; configuring the switches into a third configuration begin an Auto Zero (AZ) phase with a third switch in a closed state; configuring the switches into a fourth configuration to repeat the transition of the third switch to the open state corresponding to a first configuration; configuring the switches into a fifth configuration to repeat the transition of a first switch and a second switch to the open state corresponding to a second configuration; configuring the switches into a sixth configuration to repeat the transition of the third switch to the closed state corresponding to a second configuration; and performing an AZ decision with the switches in the sixth configuration.