VCO Calibration with Adaptive Gain for PLL Jitter and Spur Control
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Solution Overview
Problem
Phase-locked loops (PLLs) in integrated circuits face challenges in managing jitter and reference spurs due to large voltage-controlled oscillator (VCO) gain, which degrades phase noise and spur performance, especially as operating frequencies increase and supply voltages scale down with advanced CMOS technologies.
Innovation Solution
Implementing a method for adaptive gain management through VCO calibration, utilizing multiple overlapped tuning sub-bands and a flexible current ratio to reduce VCO gain, and employing a ring VCO design with a low drop out regulator to minimize jitter and reference spurs without external current sources or temperature sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If large VCO gain is used to cover wide frequency range and account for PVT variations, then frequency coverage is improved, but jitter increases and phase noise performance degrades
Solution Approach 1:
The frequency tuning range is divided into multiple overlapped sub-bands. Each sub-band is tuned by a separate current source, allowing the VCO to operate with lower gain within each sub-band while collectively covering the entire wide frequency range. This segmentation resolves the contradiction by maintaining frequency coverage through multiple segments while reducing jitter within each segment.
Solution Approach 2:
The VCO gain is made dynamically adjustable through calibration circuits that adapt the VCO operating point based on process, voltage, and temperature conditions. This dynamic adaptation allows the system to maintain optimal jitter performance across varying conditions while preserving wide frequency coverage capability.
2Adaptability or versatility
If large control voltage range is used to cover wide frequency range, then frequency coverage is improved, but charge pump up and down current mismatch increases
Solution Approach 1:
The control voltage range is segmented into multiple smaller ranges, each corresponding to a frequency sub-band. By using separate current sources for each sub-band, the control voltage swing within each segment is reduced, minimizing charge pump current mismatch and thereby reducing reference spurs while maintaining overall wide frequency coverage.
Solution Approach 2:
The system changes operating parameters (current ratios, control voltage levels) across different frequency sub-bands to optimize performance. By adjusting these parameters segmentally rather than using a single large range, the system reduces harmful effects like reference spurs while preserving frequency coverage.
3Use of energy by moving object
If supply voltage is scaled down with advanced CMOS technologies, then power consumption is reduced, but VCO gain increases and phase noise performance degrades
Solution Approach 1:
The segmented current source approach allows the VCO to achieve the required frequency tuning range through multiple small-step adjustments rather than relying on high gain from a single large voltage swing. This enables lower supply voltage operation while maintaining phase noise performance.
Solution Approach 2:
The system changes the relationship between control voltage and frequency tuning by introducing multiple current sources with different ratios. This parameter change allows efficient operation at lower supply voltages while maintaining adequate VCO gain control and phase noise performance through calibrated current ratios.
Data Source
AI summary
An apparatus comprises a first circuit and a second circuit. The first circuit may be configured to generate an output signal having a first frequency in response to a voltage level of a first input signal and a value of a second input signal. The second circuit may be configured to determine the value of the second input signal based on a reference frequency signal, the first frequency of the output signal, a reference voltage, and a value representing a target frequency for the output signal.