Interleaved ADC Channel Matching via Random Dither Correlation
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Solution Overview
Problem
Interleaved analog-to-digital converters (ADCs) face errors due to gain, timing, and bandwidth mismatches between channels, which existing techniques fail to adequately calibrate, leading to distortion and performance degradation.
Innovation Solution
The introduction of a correlation-based method involving the injection of a random or pseudo-random dither signal into the sampling network of ADCs, using the Least Mean Squares (LMS) algorithm to estimate gain coefficients, allowing for digital or analog corrections to match channel characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If interleaved ADC channels operate in parallel with different timing, then conversion speed and productivity are improved, but timing mismatch and phase offset errors occur between channels
Solution Approach 1:
The patent applies preliminary action by injecting a dither signal into the sampling network before the actual conversion process. This allows the system to pre-characterize each channel's timing, gain, and bandwidth characteristics through correlation-based measurement. The measured mismatch parameters are then stored and used to correct subsequent conversions, enabling high-speed parallel operation while maintaining accuracy through pre-established correction data.
Solution Approach 2:
The patent implements feedback by measuring the actual timing, gain, and bandwidth of each interleaved channel using correlation techniques on the dither signal response. These measured parameters are fed back to calculate correction factors that are applied to the channel outputs. This closed-loop approach continuously compensates for mismatches, allowing the system to maintain high conversion speed while correcting timing and phase offset errors that would otherwise degrade measurement precision.
2Productivity
If multiple interleaved channels are used to increase conversion rate, then productivity is improved, but gain mismatch and bandwidth mismatch cause distortion
Solution Approach 1:
The system performs preliminary characterization of each channel's gain and bandwidth by analyzing the correlation between the injected dither signal and the channel output. This pre-measurement establishes baseline parameters for each channel, allowing the system to compute correction factors before normal operation begins. This preliminary calibration enables multiple channels to operate in parallel at high conversion rates while maintaining consistent gain and bandwidth across all channels.
Solution Approach 2:
The patent applies parameter changes by measuring and adjusting the gain and bandwidth parameters of each channel individually. Through correlation-based measurement of the dither signal response, the system determines actual gain and bandwidth values for each channel. Correction factors are then applied to equalize these parameters across all channels, transforming them from mismatched states to matched states. This enables high conversion rates with multiple channels while eliminating gain and bandwidth mismatch distortion.
3Measurement precision
If dither signal is injected into sampling network, then calibration accuracy is improved, but additional circuit complexity and energy consumption are introduced
Solution Approach 1:
The patent applies universality by designing the dither injection circuit to serve multiple calibration functions simultaneously. The same dither signal and measurement infrastructure are used to characterize timing mismatch, gain mismatch, and bandwidth mismatch across all channels. This multi-functional approach achieves comprehensive calibration accuracy without proportionally increasing circuit complexity, as a single injection point and measurement system handle multiple calibration objectives.
Solution Approach 2:
The system applies self-service by using the ADC's own existing infrastructure to perform the calibration measurements. The dither signal is injected into the sampling network and measured through the existing ADC channels and digital signal processing paths. This self-calibration approach avoids the need for external calibration equipment or separate measurement circuits, achieving high calibration accuracy while minimizing additional circuit complexity and energy consumption.
4Measurement precision
If correlation-based measurement with dither injection is used, then mismatch detection precision is improved, but processing time and computational requirements increase
Solution Approach 1:
The patent applies preliminary action by performing the correlation-based measurement during an initial calibration phase before normal high-speed conversion begins. The dither signal is injected and the correlation measurements are completed in advance, establishing correction factors that are then applied during normal operation. This separates the time-consuming precise measurement from the speed-critical conversion process, achieving high mismatch detection precision without sacrificing conversion speed during actual operation.
Solution Approach 2:
The system applies periodic action by implementing calibration at specific intervals rather than continuously. The dither signal injection and correlation measurement can be performed periodically to update correction factors, or only once during initialization. This periodic approach maintains high measurement precision when needed while minimizing the time lost to calibration activities, allowing the system to spend most of its time in high-speed conversion mode.
Data Source
AI summary
A method and a corresponding device for calibrating an interleaved analog-to-digital converter (ADC) involve injecting a pulsed, substantially-random signal into a plurality of channels in the ADC. After the substantially-random signal is injected, a gain correlation value is determined for each channel, which value indicates a degree of correlation between the injected substantially-random signal and an output of the respective channel. The gain correlation values are then compared to determine a degree of mismatch between the channels. At least one of the channels is calibrated as a function of the determined degree of mismatch.