FPGA Waveform Capture with Carry-Chain Timing Calibration
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Field-programmable gate arrays (FPGAs) based time-to-digital converters (TDCs) face challenges in generating reliable picosecond time-intervals for calibration and suffer from signal distortions due to uncontrollable delays and variations in logic elements, while digital storage oscilloscopes (DSOs) on FPGAs are considered inferior to commercial products.
Innovation Solution
A 5 picosecond-resolution time-to-digital converter (TDC)/ultra-fast digital oscilloscope (DO) hybrid, known as the Waveform-Capture-Device (WCD), implemented on an FPGA, uses dynamic phase-shifting (DPS) for calibration and employs carry-chains and tapped delay lines to capture digital waveforms without encoding, allowing for precise measurement of complex GHz frequency waveforms at picosecond time intervals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If FPGAs are used to implement TDCs for picosecond resolution measurements, then versatility and reconfigurability are improved, but signal distortions occur due to uncontrollable delays and variations in logic elements
Solution Approach 1:
The patent extracts the signal path from the general-purpose logic elements of the FPGA and routes it through dedicated carry-chain elements. These carry-chains provide controlled, predictable delay paths that are separate from the uncontrollable logic element delays, thereby eliminating signal distortions while maintaining FPGA reconfigurability for other functions
Solution Approach 2:
The patent introduces carry-chain elements as intermediary structures between the input signal and the measurement registers. These carry-chains act as mediators that provide stable, controlled delay paths with known propagation characteristics, bridging the gap between the reconfigurable FPGA fabric and the precision measurement requirements
2Measurement precision
If conventional TDC calibration methods are used on FPGAs, then measurement accuracy can be improved, but calibration complexity and resource requirements increase
Solution Approach 1:
The patent performs calibration measurements during the manufacturing process before the TDC is deployed for actual measurements. This preliminary calibration establishes accurate lookup tables that map digital carry-chain states to precise time interval values, eliminating the need for complex real-time calibration procedures and reducing operational complexity
Solution Approach 2:
The patent implements a self-calibrating system where the TDC uses its own internal carry-chain structure and registered output signals to perform calibration measurements. The system automatically captures waveform data at different delay settings and generates calibration lookup tables without requiring external calibration equipment or complex external procedures
3Ease of manufacture
If digital storage oscilloscopes are implemented on FPGAs to capture waveforms, then cost and flexibility are improved, but measurement precision is inferior to commercial products
Solution Approach 1:
The patent merges the functionality of a digital storage oscilloscope with a time-to-digital converter within a single FPGA-based WCD. By combining these two previously separate functions, the system achieves precise time interval measurements (5 ps resolution) alongside waveform capture capabilities, eliminating the need for separate commercial instruments while maintaining high precision
Solution Approach 2:
The patent changes the fundamental measurement parameter from voltage-based oscilloscope sampling to time-based carry-chain state registration. This parameter change enables picosecond-resolution time interval measurements by registering the state of carry-chain elements at precise time intervals, achieving measurement precision comparable to or exceeding commercial products while using FPGA technology
Data Source
AI summary
A waveform capture device (WCD) is a flexible measurement system capable of recording complex digital signals on trillionth-of-a-second (ps) time scales. The WCD may be implemented via modular code on an off-the-shelf field-programmable gate-array (FPGA), and incorporates both time-to-digital converter (TDC) and digital storage oscilloscope (DSO) functionality. The device captures a waveform by taking snapshots of a signal as it propagates down an ultra-fast transmission line known as a carry chain (CC). It may be calibrated via a dynamic phase-shifting (DPS) method that requires substantially less data and resources than conventional techniques.