SAR ADC Auto-Zero Switching for Charge Injection Capture
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Solution Overview
Problem
Current multi-stage SAR ADC circuits face challenges in accurately capturing switch charge injections and comparator kickback effects, leading to higher offset voltages that hinder high-precision and high-performance applications due to incomplete estimation and correction of errors from various sources within the switch network.
Innovation Solution
The implementation of a multi-stage SAR ADC circuit with an enhanced Auto Zero (AZ) phase that measures and corrects for charge injection and comparator kickback noise by repeating switch transitions during the AZ phase, ensuring accurate compensation for multiple sources of error, including charge injection, capacitor leakage, and comparator kickback noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional Auto Zero phase is used in multi-stage SAR ADC circuits, then the circuit operation is simple and fast, but the offset voltage is high due to incomplete capture of charge injection and comparator kickback effects
Solution Approach 1:
The AZ phase is segmented into multiple distinct configurations (first, second, third configurations with different switch states) to separately capture different error sources. Each configuration targets specific charge injection and kickback effects, allowing precise measurement and correction of offset voltage by breaking down the complex error capture into manageable segments.
Solution Approach 2:
The patent implements periodic switching actions during the AZ phase where switches are repeatedly transitioned between states in a structured sequence. This periodic action allows the circuit to sample and capture charge injection and comparator kickback effects at multiple moments, improving offset voltage measurement by accumulating error data across periodic cycles.
2Measurement precision
If switch transitions are repeated during AZ phase to capture charge injection effects, then measurement precision improves, but the time required for the AZ phase increases
Solution Approach 1:
The AZ phase is performed preliminarily before the main conversion process to capture and correct offset voltage errors. By pre-measuring charge injection and comparator kickback effects through structured switch configurations, the circuit prepares correction values in advance, improving subsequent conversion accuracy without adding time to the critical conversion path.
Solution Approach 2:
The patent creates simplified copies of the conversion phase switch configurations specifically for the AZ phase. These copied configurations replicate the essential switching patterns needed to capture error effects, allowing accurate error measurement without requiring the full complexity and time of an actual conversion cycle.
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.