Auxiliary ADC Calibration for Delay-Path Linearity Correction
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Solution Overview
Problem
Delay domain analog-to-digital converters (ADCs) exhibit non-linear behavior due to mismatches between calibration and functional paths, limiting their performance in terms of spurs, spurious-free dynamic range, and harmonic distortion.
Innovation Solution
An auxiliary ADC-based calibration system is implemented, using a calibration path with a digital-to-analog converter (DAC) to update look-up tables (LUTs) and correct non-linearities by comparing outputs with reference signals, thereby improving the linearity of the ADCs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If delay domain ADC is used for fast signal conversion, then conversion speed is improved, but non-linearity increases due to path mismatches
Solution Approach 1:
An auxiliary ADC is introduced as an intermediary device with a separate calibration path that does not interfere with the functional delay path. This auxiliary ADC measures the actual delay values while a lookup table stores correction data, mediating between the non-linear delay domain conversion and the linear output requirement
Solution Approach 2:
The lookup table is pre-calibrated with correction data that compensates for path mismatches before actual signal conversion occurs. This preliminary calibration action eliminates non-linearities in advance, allowing the delay domain ADC to operate at full speed without real-time correction complexity
2Manufacturing precision
If calibration path is added to correct non-linearity, then conversion precision is improved, but device complexity increases
Solution Approach 1:
The auxiliary ADC shares the same delay cells and voltage-to-delay converter as the functional path, merging calibration and measurement functions into a single physical structure. This reduces component count while maintaining calibration capability
Solution Approach 2:
The auxiliary ADC creates a copy of the functional path's delay measurement capability, using identical delay cells to measure delay values without affecting the main conversion path. This copying approach simplifies the calibration system by reusing existing hardware rather than adding completely separate calibration components
Data Source
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AI summary
In an example, a system (100) includes an input channel (102) and a voltage to delay converter (V2D) (112) coupled to the input channel (102). The system (100) also includes a first multiplexer (114) coupled to the V2D (112) and an analog-to-digital converter (ADC) (140) coupled to the first multiplexer (114). The system (100) includes a second multiplexer (124) coupled to the input channel (102) and an auxiliary ADC (126) coupled to the second multiplexer (124). The system (100) includes calibration circuitry (128) coupled to an output of the auxiliary ADC (126), where the calibration circuitry (128) is configured to correct a non-linearity in a signal provided by the input channel (102). The calibration circuitry (128) is also configured to determine the non-linearity of the signal provided to the ADC (140) relative to the signal provided to the auxiliary ADC (126).