Hybrid Current-Starved Phase-Interpolation Circuit for PLLs
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Solution Overview
Problem
Voltage-controlled delay (VCD) elements in phase-locked loops (PLLs) and delay-locked loops (DLLs) face challenges with nonlinear voltage-to-frequency transfer characteristics, leading to variable VCO gain and sensitivity to process, voltage, and temperature variations, while current-starved ring VCOs provide wide tuning range but at the cost of high phase noise and limited tuning range.
Innovation Solution
A hybrid current-starved phase-interpolation method for voltage-controlled delay lines and oscillators, combining coarse tuning via current-starved control for wide range and fine tuning via phase interpolation for linear characteristics, with programmable reference voltage for noise optimization, and differential control for improved noise immunity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If current-starved method is used for voltage-controlled delay, then wide tuning range is achieved, but nonlinear voltage-to-frequency transfer characteristic and high phase noise occur
Solution Approach 1:
The VCD element is divided into two independent control paths: a current-starved control path for coarse tuning and a phase-interpolation control path for fine tuning. This segmentation allows each path to optimize for its specific function while avoiding the drawbacks of using a single method for both tuning ranges.
Solution Approach 2:
The patent merges the current-starved delay cell with a phase-interpolation circuit to create a hybrid VCD element. The current-starved path provides wide tuning range while the phase-interpolation path provides linear voltage-to-frequency characteristics and low phase noise, combining the advantages of both methods.
2Reliability
If phase-interpolation method is used for voltage-controlled delay, then linear voltage-to-frequency characteristic and low phase noise are achieved, but limited tuning range occurs
Solution Approach 1:
The control range is segmented into coarse tuning (handled by current-starved path) and fine tuning (handled by phase-interpolation path). This allows the phase-interpolation method to focus on providing low-noise fine adjustment without being burdened by the requirement to provide wide overall tuning range.
Solution Approach 2:
The phase-interpolation circuit is merged with current-starved control to create a hybrid structure where the phase-interpolation path excels at fine tuning with linear characteristics while the current-starved path extends the overall tuning range.
3Adaptability or versatility
If current-starved ring VCO is used, then wide tuning range is provided, but high sensitivity to process, voltage, and temperature variation occurs
Solution Approach 1:
The control function is segmented into coarse tuning (current-starved) and fine tuning (phase-interpolation), allowing the phase-interpolation path to compensate for PVT variations in the current-starved path, thereby reducing overall sensitivity to process, voltage, and temperature changes.
Solution Approach 2:
The patent changes the control parameters by introducing dual control voltages (one for current-starved path, one for phase-interpolation path) and uses a programmable reference voltage to set the output swing, optimizing performance across PVT variations.
Data Source
AI summary
A hybrid circuit includes a current-starved voltage-controlled circuit configured to adjust a first type of signal difference, and a phase-interpolated voltage controlled circuit configured to adjust a second type of signal difference. The current-starved circuit and the phase-interpolated circuit cooperate to provide improved operational performance of the hybrid circuit.