Time-to-Digital Converter Calibration for Nonlinear Output Correction
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Solution Overview
Problem
Time-to-digital converters (TDCs) suffer from non-idealities such as offset, gain, and non-linearity errors, which affect their accuracy in measuring time differences.
Innovation Solution
A calibration system and method that involves providing input signals with known time differences to the TDC, storing a mapping between the TDC output and the known time difference in a mapping table, and using digital post-processing to compensate for these errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a time-to-digital converter (TDC) is used to measure time differences, then time measurement capability is provided, but non-idealities such as offset, gain, and non-linearity errors reduce measurement precision
Solution Approach 1:
The patent applies preliminary action by performing calibration before actual time difference measurements. Known time difference values are provided to the TDC, and mapping values are stored in advance to compensate for non-idealities. This pre-calibration approach establishes correction data that improves subsequent measurement accuracy without affecting the TDC's inherent time measurement capability.
2Measurement precision
If calibration signals with known time differences are provided to the TDC, then measurement precision is improved, but device complexity increases due to additional calibration circuitry
Solution Approach 1:
The patent merges the calibration function with the existing TDC structure by using the same input interface and integrating the mapping table within the TDC device. The calibration circuitry shares resources with the measurement path, and the mapping table is stored in the same digital memory structure, thereby reducing overall device complexity while maintaining measurement precision improvements.
Solution Approach 2:
The TDC performs self-calibration by processing its own output values through the mapping table. The device uses its measured output to retrieve corresponding mapping values and generate compensated time difference values without requiring external calibration equipment during operation. This self-service approach reduces the complexity of external calibration systems.
3Measurement precision
If mapping values are stored in a digital memory for each pair of calibration signals, then measurement precision is enhanced, but loss of time occurs during calibration and mapping operations
Solution Approach 1:
The patent performs the time-consuming calibration process in advance, storing mapping values in a digital memory table before actual time difference measurements. During operation, the system only needs to retrieve pre-computed mapping values and apply simple compensation calculations, significantly reducing the time loss during actual measurements while maintaining enhanced precision.
Solution Approach 2:
The patent replaces complex real-time calibration mechanics with a lookup table approach. Instead of performing complex calibration calculations during measurement, the system substitutes mechanical/computational calibration operations with simple memory retrieval and table-lookup operations, reducing processing time while maintaining measurement precision.
Data Source
AI summary
Digital post-processing of time-to-digital converter (TDC) output data can be used to map each TDC code to the ideal one, but this requires knowing the TDC input-output mapping. Therefore, a calibration system and method are provided for characterizing operation of a TDC to compensate for non-idealities. Input signals having a known time difference are provided to the TDC, and a mapping between the TDC output and the known time difference is stored in a mapping table. With the described method, it is possible to input an input ramp of very low slope to construct this mapping to a desired resolution during a background calibration procedure. This characterizing and mapping can be performed across a range of input signals having different known time differences. After calibration, a mapping table can be used by a mapping circuit of the TDC or by a digital post-processing function to provide a compensated TDC output.