Asynchronous Time-Interleaved Digitizer Calibration for Clock Skew
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Solution Overview
Problem
Test and measurement instruments with asynchronous time-interleaved digitizers face limitations in calibration due to hardware mismatches and environmental drifts, particularly when built-in calibration oscillators do not span the entire range of potential signal sources, leading to suboptimal performance.
Innovation Solution
The implementation of a compensation oscillator and a Look Up Table (LUT) system that allows for real-time calibration and correction of phase and amplitude errors, using a tunable compensation oscillator to determine and adjust for errors, and a LTP filter with pre-calculated coefficients stored in a two-dimensional array to address hardware mismatches and environmental changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If factory calibration is performed with built-in calibration oscillators, then initial calibration is achieved, but calibration accuracy deteriorates when oscillators do not span the full frequency range of potential signal sources
Solution Approach 1:
An external signal source is introduced as an intermediary to provide calibration signals across the full frequency range of the digitizer. This external source mediates between the limitation of built-in oscillators and the requirement for comprehensive calibration coverage, enabling accurate calibration at frequencies beyond oscillator capabilities.
Solution Approach 2:
The system performs preliminary characterization of hardware mismatches across the full frequency range using the external signal source before actual operation. This preliminary action creates a lookup table of correction values that compensates for frequency-dependent errors, ensuring accurate calibration is ready in advance for any operating frequency.
2Reliability
If hardware adjustments are made for mixing clock amplitude and phase, then interleave mismatch spurs are reduced, but device complexity increases
Solution Approach 1:
Physical hardware adjustments for amplitude and phase calibration are replaced with digital signal processing. The system uses digital mixers and lookup tables to correct interleave mismatch spurs, eliminating the need for mechanical or manual hardware adjustments while maintaining signal fidelity.
Solution Approach 2:
The system changes calibration parameters (amplitude and phase) dynamically based on operating conditions rather than requiring fixed hardware adjustments. By storing multiple calibration values in lookup tables and selecting appropriate parameters based on frequency and temperature, the system reduces complexity while improving reliability.
3Adaptability or versatility
If real-time calibration is implemented with tunable oscillators, then calibration adaptability to environmental changes is improved, but device complexity and cost increase
Solution Approach 1:
The external signal source acts as a mediator, providing the full-frequency calibration signals needed for real-time calibration without requiring a complex tunable oscillator in the instrument. This intermediary approach achieves environmental adaptability while avoiding the complexity and cost of building-in wide-range tunable oscillators.
Solution Approach 2:
The system performs calibration periodically using the external signal source rather than requiring continuous operation of complex tunable oscillators. By scheduling calibration at appropriate intervals and using the simpler external source, the system achieves environmental adaptability with reduced complexity.
Data Source
AI summary
A test and measurement instrument includes a coefficient storage facility coupled to a programmable filter. The coefficient storage facility is configured to store at least two pre-determined filter coefficient sets, and configured to pass a selected one of the at least two pre-determined filter coefficient sets to the filter based on a measurement derived using a compensation oscillator. The measurement may include clock delay and clock skew. In some examples the test and measurement instrument may additionally adjust clock delay and/or clock skew in addition to selecting appropriate filter coefficients.