FPGA TDC Delay-Line Coding for Higher Time Resolution
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Solution Overview
Problem
FPGAs face limitations in time resolution and accuracy due to resource constraints, jitter, non-linear behavior, and routing delays, which affect TDC performance.
Innovation Solution
The FPGA design includes a first delay line part, a code conversion part, and a calculation part to determine time differences using a conversion code, compensating for jitter and improving resolution by arranging thermometer codes based on data path delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a TDC is implemented using an FPGA with limited resources, then the device can be programmed and reconfigured, but the time resolution and measurement precision are limited due to resource constraints
Solution Approach 1:
The delay line is divided into multiple segments with different delay characteristics. Each segment processes a portion of the time interval measurement, allowing the system to achieve high resolution without requiring a single long delay line that would consume excessive FPGA resources. The segmentation enables parallel processing of time measurements across multiple channels.
Solution Approach 2:
The patent transitions from a single-dimensional delay line approach to a multi-dimensional architecture by incorporating both time-domain delay elements and amplitude-domain interpolation. This dimensional expansion allows the TDC to achieve higher resolution measurements using the same FPGA resources by utilizing multiple measurement dimensions simultaneously.
2Productivity
If the clock frequency is increased to improve measurement speed, then productivity increases, but jitter introduces errors that worsen measurement precision
Solution Approach 1:
The system incorporates feedback mechanisms that monitor and compensate for jitter effects in real-time. By continuously adjusting the measurement process based on detected jitter patterns, the TDC maintains high measurement speed while correcting precision errors that would otherwise accumulate at higher clock frequencies.
Solution Approach 2:
The patent applies preliminary calibration and compensation techniques before actual measurements are taken. By pre-characterizing the delay elements and establishing correction factors in advance, the system prepares for high-speed operation while having predetermined methods to counteract jitter-induced errors during measurement.
3Measurement precision
If the number of logic elements and routing distance is increased to improve resolution, then measurement precision improves, but routing capacitance increases causing delay
Solution Approach 1:
Different regions of the FPGA are assigned delay elements with locally optimized characteristics. By tailoring the delay properties to specific spatial locations and routing paths, the system achieves high overall resolution while minimizing the cumulative capacitance effect. Each local region is optimized for its specific function rather than using a uniform approach throughout.
4Measurement precision
If interpolation techniques are used to increase resolution, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent uses copying techniques where simple delay element patterns are replicated multiple times across the FPGA fabric. Rather than implementing a single complex interpolation circuit, the system creates multiple copies of basic functional units that work together to achieve high resolution, thereby reducing the complexity of individual components while maintaining overall precision.
Data Source
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AI summary
an FPGA including a first delay line part to which an input pulse having a width corresponding to a time difference between generation times of a start signal and a stop signal is inputted; a code conversion part that converts and outputs an order of elements of a thermometer code outputted from the first delay line part; and a calculation part that determines the generation time difference using a conversion code outputted from the code conversion part, wherein the conversion code is an arrangement of an order of elements of the thermometer code according to a predetermined criterion, and the predetermined criterion is a data path delay from an output node of the input pulse to output nodes of each of a plurality of flip-flops included in the first delay line part.