Multi-Curve PLL Frequency Synthesizer with Closed-Loop VCO Search
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Solution Overview
Problem
Conventional frequency synthesizers using multi-curve VCOs face challenges in selecting the optimal operating curve for wide frequency range coverage, often resulting in sub-optimal performance due to open loop control methods that do not account for noise and variations in process, voltage, and temperature, leading to jitter issues and inefficient frequency step size.
Innovation Solution
A digital control circuit implementing a closed loop curve search method with a binary jump algorithm is introduced, which narrows the control voltage range and increases charge pump current during curve search operations to quickly converge on the optimal VCO operating curve, ensuring robustness and accuracy in selecting the optimal operating curve for target frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single-curve VCO with large VCO gain is used to cover wide frequency range, then the frequency range coverage is improved, but the jitter increases due to large sensitivity to control voltage changes
Solution Approach 1:
The VCO operating range is segmented into multiple curves, each with smaller VCO gain. The system selects appropriate curves based on target frequency, avoiding the need for a single high-gain curve that causes jitter. This segmentation allows wide frequency coverage while maintaining low jitter in each segment.
Solution Approach 2:
The system dynamically selects different VCO curves based on the target frequency and control voltage range. This dynamic adaptation allows the VCO to operate on the most appropriate curve for the current frequency requirement, optimizing both range coverage and jitter performance.
2Device complexity
If open loop control method is used to select VCO operating curve, then the device complexity is reduced, but the manufacturing precision deteriorates due to inability to account for noise and variations
Solution Approach 1:
The system employs closed-loop feedback to select VCO operating curves. The feedback mechanism accounts for noise and process variations by monitoring actual VCO performance and adjusting curve selection accordingly, significantly improving curve selection accuracy over open-loop methods.
Solution Approach 2:
The system changes operating parameters (control voltage range, charge pump current) based on the selected curve and operating conditions. This parameter adaptation allows the system to optimize performance for each specific operating point, improving manufacturing precision.
3Device complexity
If conventional curve search method is used, then the search process is simple, but the search time increases due to lack of optimized search strategy
Solution Approach 1:
The system performs preliminary actions by narrowing the control voltage range and increasing charge pump current during curve search operations. This preparation reduces the search space and accelerates convergence, significantly reducing search time without requiring complex algorithms.
Solution Approach 2:
The system applies different control strategies to different phases of the curve search process. During search, it uses narrowed voltage range and increased current; during normal operation, it returns to standard parameters. This localized optimization reduces search time efficiently.
Data Source
AI summary
A phase-locked loop circuit using a multi-curve voltage-controlled oscillator (VCO) having a set of operating curves, each operating curve corresponding to a different frequency range over a control voltage range. The phase-locked loop circuit includes a digital control circuit configured to generate a curve select signal using a closed loop curve search operation to select one of the operating curves in the multi-curve VCO, the selected operating curve being used by the VCO to generate an output signal with an output frequency being equal or close to a target frequency of the phase-locked loop. In one embodiment, the digital control circuit implements a binary jump method and an operating curve is selected when the operating curve has an output frequency meeting the target frequency with the control voltage being within a first voltage range being a narrowed and centered voltage range within the control voltage range.