Random Chopper Calibration for Low-Noise Data Converters
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Random chopping in data converters is limited by non-idealities in the chopper circuit, leading to severe degradation in noise floor and performance, which existing calibration techniques fail to adequately address.
Innovation Solution
The implementation of a calibration technique using correlators and existing calibrations within the data converter, employing a least mean squares (LMS) algorithm to correct offset and gain errors in the random chopper circuit, thereby enhancing the effectiveness of chopping and relaxing design constraints on analog circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If random chopping is used in data converters, then offset errors and even-order harmonics are reduced, but non-idealities in the chopper circuit cause severe degradation in noise floor and performance
Solution Approach 1:
The patent applies preliminary calibration action by measuring and storing correction terms for chopper non-idealities before actual signal conversion. The system pre-characterizes the chopper circuit's gain and offset errors, then uses these pre-computed correction terms during operation to compensate for the non-idealities that would otherwise degrade the noise floor and performance.
Solution Approach 2:
The patent implements feedback by using the measured output signal to update and refine correction terms for chopper non-idealities. The system continuously monitors the actual performance degradation and adjusts the correction terms accordingly, creating a closed-loop system that compensates for the noise floor degradation caused by chopper non-idealities.
2Measurement precision
If existing calibration techniques are used, then some errors are corrected, but they fail to adequately address the non-idealities in the random chopper circuit
Solution Approach 1:
The patent changes the calibration parameters by specifically targeting chopper circuit non-idealities (gain and offset errors) rather than general ADC errors. The system measures and corrects parameters specific to the chopper circuit's performance degradation, including noise floor elevation and distortion, using correction terms that are specifically tailored to compensate for these chopper-induced non-idealities.
3Reliability
If calibration techniques are applied to correct chopper non-idealities, then noise floor and performance are improved, but device complexity increases
Solution Approach 1:
The patent applies self-service by implementing background calibration that operates automatically during normal converter operation without requiring external calibration equipment or manual intervention. The system uses its own output signal to measure and update correction terms for chopper non-idealities, making the calibration process self-contained and eliminating the need for complex external calibration apparatus.
Solution Approach 2:
The patent merges the calibration function with the normal signal conversion operation by implementing background calibration that occurs simultaneously with data conversion. The correction term measurement and application are combined with the regular ADC operation, eliminating the need for separate calibration modes or additional dedicated calibration circuitry that would increase device complexity.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Random chopping is an effective technique for data converters. Random chopping can calibrate offset errors, calibrate offset mismatch in interleaved ADCs, and dither even order harmonics. However, the non-idealities of the (analog) chopper circuit can limit its effectiveness. If left uncorrected, these non-idealities cause severe degradation in the noise floor that defeats the purpose of chopping, and the non-idealities may be substantially worse than the non-idealities that chopping is meant to fix. To address the non-idealities of the random chopper, calibration techniques can be applied, using correlators and calibrations that may already be present for the data converter. Therefore, the cost and digital overhead are negligible. Calibrating the chopper circuit can make the chopping more effective, while relaxing the design constraints imposed on the analog circuitry.