CT ADC Calibration Using DAC Mismatch Error Correction
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Solution Overview
Problem
Continuous-time (CT) analog-to-digital converters (ADCs) face inaccuracies in transfer function estimation due to mismatch in the injection DAC, leading to poor noise spectral density (NSD) at the ADC output.
Innovation Solution
Implement a system comprising a delay circuit, sub-ADC circuit, first sub-DAC circuit, error estimation circuit, and error correction circuit to generate a digital error-correction signal, enhancing transfer function accuracy by combining residue and sub-ADC signals with the digital correction signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a pseudo random bit sequence is injected using a DAC to estimate the transfer function, then the transfer function can be measured, but mismatch in the injection DAC introduces errors in the transfer function estimation and results in poor NSD at the ADC output
Solution Approach 1:
The patent implements a feedback mechanism where the ADC output is fed back through a digital-to-analog converter and combined with the delayed input signal. This feedback path allows for continuous monitoring and correction of transfer function estimation errors, improving measurement precision while maintaining NSD performance through iterative refinement of the estimated transfer function.
Solution Approach 2:
The patent introduces an intermediary processing stage that separates the transfer function estimation path from the main conversion path. By using an intermediate signal processing block that independently estimates the transfer function and then applies corrections, the system avoids direct interference between the measurement process and the conversion process, thereby resolving the contradiction between measurement accuracy and NSD performance.
2Measurement precision
If the ADC uses a complex calibration system to improve transfer function accuracy, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent designs the feedback path and signal processing blocks to serve multiple functions: they are used both for transfer function estimation and for the main ADC conversion process. This multi-functionality reduces the need for separate dedicated calibration components, thereby improving measurement precision without proportionally increasing device complexity.
Solution Approach 2:
The ADC system performs its own transfer function estimation and correction using internally available signals and components. The feedback path utilizes existing ADC outputs and input signals to self-calibrate the transfer function, eliminating the need for external calibration equipment or complex separate calibration circuits, thus improving precision while keeping complexity manageable.
Data Source
AI summary
CT ADCs based on continuous-time residue generation systems require accurate estimation of analog transfer functions. This is done by using a pseudo random bit sequence, injected using a DAC, that traverses the transfer function to be measured. Mismatch in the injection DAC introduces errors in the transfer function estimation and results in poor NSD at the ADC output. Techniques are described to improve the accuracy of the transfer function estimate despite DAC mismatch and despite the presence of an input signal.