Redundant Coarse-Fine TDC Correction for Quantizer Mismatch
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Solution Overview
Problem
Time-to-digital converters (TDCs) face challenges due to mismatch issues between coarse and fine quantizers, which reduce resolution and make implementation problematic, especially when trying to combine counter-based and pulse-based TDCs into a single circuit.
Innovation Solution
The implementation of a combined coarse-fine TDC with redundancy, where the coarse and fine TDCs overlap to provide correction through a compare and correction circuit, ensuring accurate time or frequency quantization without offset errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If counter-based TDC and pulse-based TDC are combined into a single circuit, then the measurement range is extended to arbitrarily large intervals with high resolution, but mismatch in the sampling instant between the two quantizers reduces the resolution to that of the coarse quantizer
Solution Approach 1:
The patent implements a nested structure where the fine quantizer's output range is divided into sub-ranges, and the coarse quantizer provides select signals for these sub-ranges. The fine quantizer is nested within each coarse quantizer sub-range, allowing both to operate simultaneously without mismatch errors. The coarse quantizer's select signals enable the appropriate fine quantizer sub-range to be active, creating a hierarchical measurement system that maintains high resolution across arbitrarily large intervals.
2Measurement precision
If separate loop filter and detection circuitry are used for coarse and fine quantizers, then each quantizer can be independently optimized, but the device complexity increases
Solution Approach 1:
The patent merges the loop filter and detection circuitry into a unified digital processing unit that handles both coarse and fine quantizer outputs. Instead of separate analog loop filters for each quantizer, a single digital loop filter processes the combined measurement data. The detection and control functions are integrated into one digital control unit that manages both quantizers simultaneously, reducing component count while maintaining independent optimization capability through digital signal processing.
Data Source
AI summary
A time-to-digital converter utilizes both coarse and fine quantizers and addresses mismatch by using redundant bits in the coarse time representation and the fine time representation. The redundant bits are compared and if the redundant bits are the same, no mismatch correction is required but if the redundant bits are different a correction is applied to correct the redundant portion of the coarse time information. The redundant portion includes the most significant bit generated by the fine quantizer and the least significant bit of the coarse quantizer. The correction adds to or subtracts from the redundant information.