Ring Oscillator VCO Current Mirroring for Supply Ripple Immunity
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Solution Overview
Problem
Conventional phase-locked loops (PLLs) face challenges in achieving high-supply ripple immunity, leading to increased power dissipation and noisy output clock spectra due to sensitivity to power supply ripple, particularly in low-voltage environments where multiple regulation levels are required, resulting in inefficient power consumption and spur contamination.
Innovation Solution
A ring oscillator-based voltage-controlled oscillator (VCO) with improved power supply ripple immunity is implemented, utilizing a distributed regulation scheme and current mirroring techniques to reduce the impact of supply ripple, allowing operation at lower voltages and eliminating unnecessary regulation levels, thereby reducing power consumption and phase noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple levels of regulation are employed to reduce supply ripple, then supply ripple immunity is improved, but power dissipation increases and device complexity increases
Solution Approach 1:
The patent extracts the critical supply ripple filtering function from the general power regulation system and applies it specifically to the VCO supply voltage. By using a dedicated regulator only for the VCO rather than multiple levels of regulation for the entire PLL, the design achieves supply ripple immunity where needed while avoiding the power dissipation penalty of regulating all PLL blocks
Solution Approach 2:
The patent applies local quality by providing regulated supply voltage specifically to the VCO block which is sensitive to supply ripple, while other PLL blocks operate from the unregulated supply. This targeted approach improves supply ripple immunity for the critical component without increasing power dissipation across the entire system
2Reliability
If multiple levels of regulation are employed to reduce supply ripple, then supply ripple immunity is improved, but device complexity increases
Solution Approach 1:
The patent extracts the regulation function from the general PLL power supply system and applies it only to the VCO block. This selective extraction reduces device complexity by eliminating unnecessary regulation stages for non-sensitive blocks while maintaining supply ripple immunity for the critical VCO
3Reliability
If high-supply voltage is used to accommodate multiple regulation levels, then supply ripple immunity is improved, but power dissipation increases
Solution Approach 1:
The patent changes the supply voltage parameter dynamically - using high voltage only at the VCO where regulation is applied, while other blocks operate at lower unregulated voltages. This parameter change enables supply ripple immunity at the critical point without increasing overall power dissipation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides enhanced power supply ripple immunity, enabling a wider linear tuning range, reduced phase noise, and lower supply-induced spurs, allowing the PLL to operate efficiently at lower voltages (e.g., 1.2V) with similar or improved performance compared to conventional schemes, resulting in significant power savings and improved frequency stability.
Implementation Method 1
an amplifier circuit having a first input coupled to a reference voltage. A first transistor provides a first current to be mirrored that is indicative of a control voltage. The second transistor has a gate terminal coupled to a gate terminal of the first transistor and an output of the amplifier circuit
Data Source
AI summary
A ring oscillator that is more insensitive to power supply ripple utilizes an amplifier circuit having a first input coupled to a reference voltage. A current is generated that represents a control voltage supplied to the oscillator control circuit. That current is mirrored and supplied as a control current to the oscillator. An amplifier is used in a feedback loop to ensure that incremental variations in source to drain voltage of a first transistor of the current mirror is present in a second transistor of the current mirror to make the control current more immune to supply ripple.