Time-Interleaved ADC Calibration Using Coprime Bitstream Patterns
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Solution Overview
Problem
Time-interleaved analog-to-digital converters (ADCs) face challenges in calibration due to mismatches between channels, particularly timing skew, which is difficult to detect and correct, leading to accumulative errors and spectral corruption.
Innovation Solution
A signal generator is used to produce a bitstream with a specific bit pattern that shares no common factor with the number of channels, combining a lower frequency component with a higher frequency component, allowing for accurate estimation and correction of mismatches, including timing skew, using a waveform generator integrated on the same IC as the ADC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a time-interleaved ADC uses multiple parallel sub-ADCs to increase sampling rate, then the sampling rate is increased m times, but timing skew and channel mismatches cause accumulative errors and spectral corruption
Solution Approach 1:
The patent applies preliminary action by performing calibration of timing skew and channel mismatches before the actual ADC operation. A calibration signal is generated and processed through the time-interleaved ADC to measure timing offsets, and correction values are calculated in advance to compensate for these errors during normal operation, thereby maintaining high sampling rates while ensuring timing accuracy.
2Measurement precision
If traditional calibration methods are used for time-interleaved ADCs, then channel mismatches can be partially corrected, but timing skew detection and correction remain difficult and complex
Solution Approach 1:
The patent applies universality by designing a calibration signal generator that can produce multiple types of calibration signals (e.g., single-tone, multi-tone, spread-spectrum) using a single integrated circuit block. This multi-functional approach enables comprehensive calibration of both timing skew and channel mismatches without requiring separate dedicated circuits for each calibration function, thereby reducing overall system complexity while maintaining high measurement precision.
Solution Approach 2:
The patent introduces an intermediary calibration signal as a mediator between the test equipment and the ADC channels. This calibration signal passes through all sub-ADCs and carries information about timing skew and channel mismatches, which are then extracted and used to generate correction values. The intermediary signal simplifies the measurement process by encoding multiple error types into a single measurable waveform.
3Measurement precision
If calibration is performed externally, then accurate measurements can be obtained, but the calibration process requires additional external equipment and increases system complexity
Solution Approach 1:
The patent applies self-service by implementing an on-chip calibration signal generator that is integrated within the ADC itself. This self-calibration capability eliminates the need for external calibration equipment, allowing the ADC to perform its own timing skew and channel mismatch calibration using internally generated test signals, thereby reducing external equipment requirements while maintaining measurement precision.
Data Source
AI summary
Certain aspects of the present disclosure provide methods and apparatus for calibrating time-interleaved analog-to-digital converter (ADC) circuits and generating a suitable signal for such calibration. Certain aspects provide a signal generator for calibrating a time-interleaved ADC circuit having a plurality of channels. The signal generator generally includes a pattern generator configured to receive a periodic signal and to output a bitstream based on the periodic signal and a conversion circuit having an input coupled to an output of the pattern generator and configured to generate a waveform based on the bitstream. The bitstream has a bit pattern with a total number of bits that shares no common factor with a number of the channels and includes a relatively lower frequency component combined with a relatively higher frequency component.