TDC Calibration Mapping for Offset and Nonlinearity Compensation
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Solution Overview
Problem
Time-to-digital converters (TDCs) often operate with non-idealities such as offset, gain, and non-linearity errors, which affect their accuracy in measuring time differences between signals, and existing calibration methods are inadequate to fully compensate for these errors.
Innovation Solution
A calibration system and method that uses a controllable signal generator to provide pairs of calibration signals with known time differences to a TDC, and a calibration mapping circuit to store and retrieve mapping values, allowing for digital post-processing to compensate for TDC output errors and provide accurate time difference measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a TDC is used to measure time differences between signals, then time measurement capability is provided, but measurement precision deteriorates due to offset, gain, and non-linearity errors
Solution Approach 1:
The patent applies preliminary action by performing calibration before actual time difference measurements. The system pre-determines mapping values that compensate for offset, gain, and non-linearity errors, storing these compensation parameters in advance for use during operation. This preliminary calibration phase establishes the foundation for accurate subsequent measurements without requiring real-time error correction.
Solution Approach 2:
The patent implements feedback through an iterative calibration process where the TDC measures known time differences, the system analyzes the output errors, and adjusts the mapping values accordingly. The calibration circuitry continuously refines the compensation parameters based on measured deviations, creating a closed-loop system that improves measurement accuracy through feedback-driven error correction.
2Measurement precision
If calibration signals with known time differences are provided to the TDC, then measurement accuracy is improved, but device complexity increases due to additional calibration circuitry
Solution Approach 1:
The patent applies universality by designing calibration signal generators that can produce multiple pairs of calibration signals with different known time differences using the same hardware infrastructure. The calibration circuitry serves dual purposes: it generates test signals and processes TDC outputs, while the mapping value storage structure handles both calibration data and operational measurement data. This multi-functionality reduces the need for separate dedicated components for each calibration function.
Solution Approach 2:
The patent utilizes parameter changes by varying the time difference parameters of calibration signals across multiple calibration steps. Instead of adding complex hardware, the system changes operational parameters (time differences between calibration signals) to extract multiple mapping values that characterize different regions of the TDC's transfer function. This approach achieves comprehensive calibration through parameter variation rather than structural complexity.
3Measurement precision
If mapping values are stored for multiple calibration signals with different time differences, then compensation accuracy is improved, but loss of time increases during calibration
Solution Approach 1:
The patent applies partial action by implementing an optional multi-stage calibration approach where the system can perform a quick single-point calibration for basic accuracy or proceed to multi-point calibration for enhanced precision. The calibration circuitry is designed to accommodate variable calibration depth, allowing the system to stop after acquiring sufficient mapping values without requiring complete calibration of all possible time difference points, thus balancing accuracy requirements with time constraints.
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.