Voltage-Controlled Oscillator Gain Shaping for Low Jitter Stability
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Solution Overview
Problem
Conventional voltage-controlled oscillators (VCOs) face challenges in achieving low jitter while maintaining stability against manufacturing process, temperature, and voltage variations, often requiring additional frequency-calibration circuits and larger loop filters, which increase cost and circuit size.
Innovation Solution
A VCO design with dual current supply circuits and a VCO filter that distinguishes between slow and rapid input voltage changes, allowing for high gain against slow variations and low gain against noise-induced changes, eliminating the need for additional frequency-calibration circuits and reducing loop filter size and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low-gain VCO is used to reduce output jitter, then the jitter performance is improved, but the VCO becomes vulnerable to frequency variations caused by manufacturing processes, temperature, and voltage changes
Solution Approach 1:
The patent implements dynamic gain control by switching between first and second gain values based on operating conditions. The control circuit adjusts the VCO gain dynamically - using higher gain when frequency stability is needed and lower gain when jitter reduction is prioritized, thus resolving the contradiction between jitter performance and frequency stability
Solution Approach 2:
The patent changes the gain parameter of the VCO based on different operating conditions. By adjusting the gain value according to temperature, voltage, and frequency requirements, the system optimizes both jitter performance and frequency stability without being constrained by a fixed gain value
2Measurement precision
If a conventional low-gain VCO is used with frequency-calibration circuit to mitigate manufacturing variation, then the frequency accuracy is improved, but the circuit complexity and cost increase
Solution Approach 1:
The VCO performs self-calibration by using its own output frequency information to adjust its operating parameters. The control circuit monitors the VCO output and automatically adjusts the gain and operating point to maintain frequency accuracy, eliminating the need for external frequency-calibration circuits
Solution Approach 2:
The patent implements a feedback mechanism where the VCO output frequency is monitored and used to adjust the VCO operating conditions. This closed-loop control enables automatic frequency correction without additional calibration circuits, reducing system complexity while maintaining frequency accuracy
3Stability of the object's composition
If a high-gain VCO is used to tolerate temperature and voltage variation, then the frequency stability is improved, but the output jitter increases and a large-size loop filter is required
Solution Approach 1:
The system dynamically adjusts the VCO gain based on operating conditions rather than using a fixed high gain. By switching between different gain values, the system achieves frequency stability when needed while minimizing jitter in other conditions, eliminating the requirement for a large loop filter
Solution Approach 2:
The patent changes the gain parameter dynamically based on temperature, voltage, and frequency requirements. This parameter adjustment allows the system to achieve frequency stability without continuously operating at high gain, thereby reducing output jitter and eliminating the need for large loop filters
4Reliability
If a large-size loop filter is used to reduce jitter in high-gain VCO, then the output jitter is reduced, but the circuit area and cost increase
Solution Approach 1:
The VCO system performs self-adjustment by dynamically changing its gain parameter to optimize jitter performance. This self-service mechanism eliminates the need for large external loop filters, reducing circuit area while maintaining low jitter performance
Solution Approach 2:
By changing the gain parameter dynamically, the system achieves jitter reduction without requiring a large loop filter. The parameter adjustment allows the use of a compact integrated filter design, reducing both circuit area and cost
Data Source
AI summary
Disclosed is a voltage-controlled oscillator (VCO) capable of providing an effective high VCO gain against slow change of an input voltage caused by the variation of manufacturing processes, temperature, voltage, etc. and providing an effective low VCO gain against rapid change of the input voltage for reducing jitter. The VCO includes: an input circuit generating an input current according to an input voltage; a first current supply circuit generating a first output current according to the input current; a second current supply circuit generating a second output current according to the input current; a filter coupled to the input circuit and the second current supply circuit and configured to slow down the influence caused by the variation of the input current on the second current supply circuit; and an oscillating circuit generating an output clock according to the first output current and the second output current.