Interleaved ADC Background Calibration Using Alias Test Tone
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Solution Overview
Problem
Existing methods for correcting errors in time-interleaved analog-to-digital converters (ADCs) face challenges in accurately detecting and minimizing errors, especially in the presence of input signals, due to interference from noise and unwanted signals, and require costly high-pass filters or are ineffective in wideband scenarios.
Innovation Solution
A system and method that uses a narrowband background test tone to identify phase and amplitude errors, applying corrections by generating sample clocks with evenly spaced phases and performing discrete Fourier transforms to minimize errors in the interleaved signal, allowing for accurate gain mismatch and timing skew calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If a high pass filter is used to remove signal content and preserve the spectral image of the test tone, then the test tone detection is facilitated, but the filter is costly to implement due to its relatively narrow bandwidth and additional signal content in the pass band limits the accuracy
Solution Approach 1:
The patent extracts only the necessary frequency components by placing the test tone at a specific frequency where its spectral image appears at a known location after ADC processing. Instead of using a high pass filter to remove all other signal content, the method selectively extracts the spectral image at the predetermined frequency location, avoiding the need for complex narrow bandwidth filtering while maintaining accurate test tone detection capability
Solution Approach 2:
The patent introduces a predetermined frequency relationship between the test tone and the ADC sampling rate as an intermediary mechanism. By setting the test tone frequency such that its spectral image appears at a known frequency after interleaved ADC processing, the method creates a predictable intermediary pathway for error detection that eliminates the need for complex signal filtering
2Difficulty of detecting and measuring
If FFT is performed on individual ADC outputs before interleaving to detect errors, then error detection is enabled, but aliased signal spectra from wideband input signals can hide the test tone, making correction ineffective in the presence of input signals
Solution Approach 1:
The patent extracts the test tone spectral image from a specific frequency location that is predetermined based on the test tone frequency and ADC sampling parameters. By focusing detection on this specific extracted frequency component rather than performing full-spectrum FFT analysis, the method isolates the test tone information from aliased signal spectra that would otherwise hide it, enabling reliable error detection and correction even when wideband input signals are present
Solution Approach 2:
The patent applies local quality by concentrating error detection efforts on a specific frequency location (the spectral image frequency) rather than analyzing the entire frequency spectrum. This localized approach at the predetermined frequency allows accurate test tone detection without being interfered with by aliased signals from wideband input, thereby maintaining correction effectiveness in the presence of input signals
Data Source
AI summary
A system and method are provided of performing background corrections for an interleaving analog-to-digital converter (ADC). An analog input signal s1(t) is accepted having a first frequency f1 and a bandwidth (BW). The method generates a clock at frequency fs, and creates 2 sample clocks with evenly spaced phases, each having a sample clock frequency of fs/2. The method also generates a first tone signal s2(t) having a predetermined second frequency f2 outside BW. The analog input signal and the first tone signal are combined, creating a combination signal, which is sampled using the sample clocks, creating 2 digital sample signals per clock period 1/fs. The 2 digital sample signals are interleaved, creating an interleaved signal. Corrections are applied that minimize errors in the interleaved signal, to obtain a corrected digital output. Errors are determined at an alias frequency f3, associated with the second frequency f2, to obtain correction information.