Hybrid Single-Loop DLL Retiming for Low-Jitter Clock Distribution
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Solution Overview
Problem
Large-scale phased arrays face challenges in maintaining timing accuracy of the reference clock signal during distribution, with existing techniques like central star distribution being impractical and daisy chained distribution suffering from significant timing variations due to voltage and temperature fluctuations.
Innovation Solution
A delay-locked loop circuit is introduced, comprising a phase/frequency detector, charge pump, variable delay line, and controlled delay line with multiple fixed delay cells, along with an overflow detector and up/down counter to adjust delays and maintain clock signal coherence across the array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If daisy chained distribution technique is used to distribute clock signals, then the architecture becomes scalable and practical for large arrays, but timing accuracy deteriorates due to large timing variations caused by supply voltage, temperature, and load variations
Solution Approach 1:
The patent implements a delay-locked loop (DLL) with feedback mechanism that continuously monitors the output clock signal and adjusts delay elements to maintain timing accuracy. The DLL compares the phase of the output clock signal with a reference clock signal and dynamically adjusts the delay in the clock distribution path to compensate for variations caused by voltage, temperature, and load changes, thereby resolving the timing accuracy degradation in scalable daisy-chained architectures
Solution Approach 2:
The patent employs variable delay elements whose delay characteristics can be dynamically adjusted by changing control parameters (such as voltage levels or digital control codes). This allows the system to adapt the timing parameters of the clock distribution network in real-time to compensate for environmental variations, maintaining timing accuracy while preserving the scalability of the daisy-chained architecture
2Measurement precision
If central star distribution technique is used to distribute clock signals, then timing accuracy is maintained, but the architecture becomes impractical for large arrays due to prohibitive number of traces and load
Solution Approach 1:
The patent divides the clock distribution network into multiple segments or stages, where each segment uses a localized delay-locked loop to maintain timing accuracy. Instead of using a single centralized star topology with numerous traces, the system segments the distribution network into hierarchical levels, reducing the total number of traces and load while maintaining timing precision through localized feedback control in each segment
3Measurement precision
If large delay adjustments are made to correct timing errors, then timing accuracy can be restored, but noise contributions increase and performance deteriorates
Solution Approach 1:
The patent uses multiple small incremental delay adjustments rather than a single large delay correction. The delay-locked loop makes fine-grained adjustments through multiple delay elements, each contributing a small delay step, to achieve the required timing correction. This partial action approach reduces the noise contributions associated with large, abrupt delay changes while still restoring timing accuracy through cumulative small adjustments
Data Source
AI summary
A delay locked-loop includes, in part, a phase/frequency detector responsive to a reference clock signal, a charge pump responsive to the phase/frequency detector, a variable delay line responsive to an output of the charge pump to cause a delay in the reference clock signal thereby to generate an internal clock signal, and a controlled delay line that includes a multitude of fixed delay cells. The controlled delay line causes the internal clock signal to be delayed by a delay across one of the multitude of fixed delay cells in response to the output of the charge pump. The controlled delay line generates the output clock signal of the delay-locked loop. The delay locked-loop may further include an overflow detector configured to cause the selection of one of the multitude of fixed delays in response to the output of the charge pump.