Ring Oscillator Supply Damping for Stable Low-Noise VCOs
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Solution Overview
Problem
Ring oscillators face instability due to large capacitance in the feedback path, which conventional methods attempt to address by using a replica VCO, but this introduces noise and increased power consumption.
Innovation Solution
An oscillator dampening circuit is coupled to the regulator, which introduces a 'zero' to offset the 'pole' caused by the large capacitance, allowing the circuit to track changes in VCO operating conditions without using a replica, thereby reducing instability and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a large capacitance is used to filter high-frequency noise from the voltage supply of the VCO, then noise filtering is improved, but the system stability deteriorates due to a pole introduced on the feedback path
Solution Approach 1:
An oscillation dampening circuit is introduced as an intermediary component between the regulator and the VCO. This circuit includes a capacitor coupled to the regulator output and a transistor whose gate is controlled by a current mirror. The dampening circuit acts as a mediator that cancels the harmful pole effect of the large filtering capacitor while maintaining noise filtering performance.
Solution Approach 2:
The oscillation dampening circuit applies preliminary anti-action by introducing a zero that cancels the pole before the pole can cause instability. The dampening circuit proactively counteracts the destabilizing effect of the large capacitance on the feedback path, preventing oscillation rather than reacting to it after it occurs.
2Stability of the object's composition
If a replica VCO is used on the feedback path to reduce capacitor-induced instability, then system stability is improved, but noise and power consumption increase
Solution Approach 1:
The invention extracts the essential stabilizing function from the complex replica VCO approach and implements it through a simpler oscillation dampening circuit. Instead of using a full replica VCO, the patent extracts only the necessary pole-canceling functionality and implements it with a capacitor-transistor circuit controlled by a current mirror, thereby eliminating unnecessary noise and power consumption.
Solution Approach 2:
The invention changes the approach from using a voltage-controlled replica oscillator to using a current-controlled dampening circuit. By changing the control parameter from voltage to current and the function from oscillation to dampening, the system achieves stability with lower power consumption and reduced noise.
3Stability of the object's composition
If a replica VCO is used on the feedback path to reduce capacitor-induced instability, then system stability is improved, but the circuit complexity and noise increase
Solution Approach 1:
The invention extracts the essential stabilizing function from the complex replica VCO approach and implements it through a simpler oscillation dampening circuit. Instead of using a full replica VCO, the patent extracts only the necessary pole-canceling functionality and implements it with a capacitor-transistor circuit controlled by a current mirror, thereby eliminating unnecessary noise and power consumption.
Solution Approach 2:
The invention replaces the expensive and noisy replica VCO with a simpler, lower-cost oscillation dampening circuit. The dampening circuit uses basic components (capacitor, transistor, current mirror) that are less noisy and consume less power than a full replica VCO, while still achieving the desired stability.
Data Source
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AI summary
Oscillator circuits and methods are disclosed. In an embodiment, a circuit includes a voltage controlled oscillator (VCO) and a regulator coupled to a supply input of the VCO. The circuit also includes an oscillation dampening circuit coupled to an output of the regulator. A resistance or a capacitance of the oscillation dampening circuit is configured to vary based on current provided to the VCO.