Time-to-Digital Converter for Wide-Range ADPLL Phase and Frequency Detection
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Solution Overview
Problem
Existing time-to-digital converters (TDCs) in all-digital phase-locked loops (ADPLLs) can only operate effectively within a small pull-in range and fail to accurately detect frequency differences, limiting their phase-alignment accuracy and operational bandwidth.
Innovation Solution
A TDC design that includes a delay line with series-coupled delay elements, comparators, and an encoder to detect phase errors, along with a frequency detector to output frequency errors as digital codes, enabling detection of both phase and frequency differences between signals, and an ADPLL that utilizes this TDC to adjust oscillation frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a delay-line based TDC is used to detect phase difference, then phase detection capability is provided, but the pull-in range remains small and frequency difference detection is not achieved
Solution Approach 1:
The TDC is designed to perform multiple functions: it detects both phase difference between input signals and frequency difference between signals. The delay line structure enables phase detection while the frequency detector component adds frequency difference detection capability, making the system universal and applicable to a broader range of conditions including larger frequency variations.
Solution Approach 2:
The TDC is divided into distinct functional components: a delay line based converter for phase detection, a phase frequency detector, and a frequency detector. This segmentation allows each component to specialize in its function while collectively expanding the pull-in range and enabling both phase and frequency difference detection.
2Measurement precision
If loop bandwidth is decreased to reduce jitter, then phase alignment accuracy improves, but pull-in range is reduced
Solution Approach 1:
The system incorporates a frequency detector that provides feedback about frequency differences between input signals. This feedback mechanism allows the TDC to maintain accurate phase alignment while adapting to larger frequency variations, effectively expanding the pull-in range without sacrificing phase alignment accuracy.
Solution Approach 2:
The TDC dynamically adapts to frequency differences by detecting both phase and frequency errors. The frequency detector component enables the system to respond dynamically to frequency variations, maintaining stability and accuracy across a wider range of operating conditions.
3Adaptability or versatility
If a bang-bang PFD is used instead of TDC to detect phase, then pull-in range is improved, but phase-alignment accuracy deteriorates
Solution Approach 1:
The invention merges the advantages of both TDC and bang-bang PFD approaches by combining a delay line based converter with a phase frequency detector and frequency detector. This hybrid structure achieves both wide pull-in range and high phase-alignment accuracy, resolving the trade-off between these two performance parameters.
Solution Approach 2:
The combined TDC structure performs multiple detection functions with high precision: phase difference detection through the delay line and comparators, frequency difference detection through the frequency detector, and phase-frequency detection through the phase frequency detector. This multi-functional design achieves both wide adaptability and high measurement precision.
Data Source
AI summary
A time-to-digital converter (TDC) includes a converter which receives a first signal and a second signal, delays the second signal in phases using a plurality of delay elements which are coupled in series, compares the delayed second signal with the first signal, and outputs a phase error of the second signal with respect to the first signal, a phase frequency detector which receives the first signal, and a third signal from one of the nodes in the plurality of delay elements, and outputs a phase difference between the first signal and the third signal, and a frequency detector which outputs a frequency error of the second signal with respect to the first signal as a digital code using an output signal of the phase frequency detector and the second signal.