Residue Amplifier Offset Correction in Pipelined ADCs
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Solution Overview
Problem
Multi-stage Analog-to-Digital Converters (ADCs) face challenges in accurately correcting offset errors in residue amplifiers, particularly due to non-zero offset voltage errors that are amplified and difficult to track over time and environmental changes, limiting their precision and reliability.
Innovation Solution
A multi-stage ADC with an embedded offset corrector that includes a residue amplifier with a feedback capacitor, an offset capacitor, and an offset corrector circuit that filters and buffers the offset voltage, allowing for real-time correction during ADC conversions, using a low-pass filter and offset amplifier to generate and apply a filtered offset to the residue amplifier's input.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a residue amplifier is used in a multi-stage ADC to amplify the residual voltage, then the conversion speed and resolution are improved, but offset voltage errors are amplified and become difficult to track over time and environmental changes
Solution Approach 1:
The offset corrector circuit performs preliminary measurement and correction of the offset voltage before the main conversion process. By measuring the offset voltage at the input of the residue amplifier and generating a compensating signal in advance, the system eliminates offset errors before they are amplified, thus maintaining reliability while preserving the high conversion speed enabled by the residue amplifier.
Solution Approach 2:
The system implements a feedback mechanism where the offset corrector continuously monitors the offset voltage at the residue amplifier input and adjusts the compensating signal accordingly. This feedback loop ensures that offset errors are tracked and corrected in real-time, maintaining accuracy despite environmental changes while allowing the residue amplifier to operate at high speed.
2Measurement precision
If the offset voltage is measured and corrected in real-time during ADC conversions, then the accuracy is improved, but the device complexity increases
Solution Approach 1:
The offset corrector circuit is merged with the residue amplifier stage, sharing common components such as the input terminals and timing control logic. This integration allows real-time offset measurement and correction to be performed using the existing amplifier infrastructure, improving accuracy while minimizing the increase in device complexity through resource sharing.
Solution Approach 2:
The residue amplifier is designed to serve multiple functions: it amplifies the residual voltage during normal conversion operations and simultaneously serves as the measurement point for offset voltage detection. The offset corrector circuit also performs multiple tasks including offset measurement, compensating signal generation, and injection into the amplifier input. This multi-functionality reduces overall system complexity while maintaining high correction accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces offset errors by up to 75%, enabling the ADC to track changes over time and environmental conditions, thereby enhancing the accuracy and reliability of high-speed, high-resolution ADCs.
Implementation Method 1
The offset corrector measures the output of the residue amplifier, filters the output with a low-pass filter to generate a filtered offset
Implementation Method 2
a feedback capacitor connected between the first input and the first output of the residue amplifier
Data Source
Figure 1~2
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Figure 5~6
AI summary
A multi-stage pipelined Analog-to-Digital Converter (ADC) has an offset correction circuit embedded in the residue amplifier between stages. The offset corrector has a low-pass filter that filters the output of the residue amplifier, and the filtered offset is amplified and stored on an offset capacitor during an autozeroing phase of the residue amplifier. During an amplify phase of the residue amplifier, switches disconnect the amplifier from the offset capacitor and instead ground the input of the offset capacitor, and other switches connect the output terminal of the offset capacitor to the input of the residue amplifier. The offset stored on the offset capacitor is combined with the residue voltage from the first ADC stage's capacitor array and applied to an input of the residue amplifier to effectively subtract the detected offset. Two offset capacitors and sets of switches can be used to implement a differential offset corrector.