Ring Oscillator Supply Compensation for Low-Jitter High Frequencies
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Solution Overview
Problem
Ring oscillators exhibit high supply noise sensitivity (high Kvcc) and intrinsic jitter, making it challenging to generate high frequencies, especially at lower supply voltages, and existing solutions require meticulous calibration and high PSRR, limiting their applicability in high-speed applications.
Innovation Solution
A combination of a lower profile voltage regulator and partial K compensation block is used to attenuate Vcc noise, reducing supply sensitivity and easing regulator and compensator parameters, allowing operation at lower supply voltages while maintaining high-frequency operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a voltage regulator with very high PSRR is used to suppress supply noise, then supply noise sensitivity is reduced, but thermal and flicker noise of the regulator strongly impact oscillator jitter
Solution Approach 1:
The patent divides the noise filtering function into two separate stages: a first voltage regulator that provides moderate noise filtering, and a second voltage regulator that provides additional noise filtering. This segmentation allows each regulator to operate with relaxed PSRR requirements while collectively achieving high noise suppression, avoiding the jitter problem caused by a single high-PSRR regulator
Solution Approach 2:
The patent introduces an intermediary noise filter between the first and second voltage regulators. This filter acts as a mediator that further suppresses noise before it reaches the oscillator, allowing the regulators to operate with lower PSRR values while maintaining overall noise performance
2Speed
If ring oscillators are designed for high-frequency operation, then frequency generation capability is improved, but supply noise sensitivity and intrinsic jitter increase
Solution Approach 1:
The patent applies beforehand cushioning by providing multiple stages of noise filtering (first regulator, noise filter, second regulator) before the noisy oscillator signal is generated. This prior noise suppression cushions the high-frequency oscillator from supply noise, allowing it to operate at high frequencies with reduced sensitivity and jitter
3Object-affected harmful factors
If existing solutions for reducing supply sensitivity are implemented, then supply noise sensitivity is reduced, but meticulous calibration and high PSRR are required, limiting applicability
Solution Approach 1:
The patent changes the approach from requiring high PSRR values to using multiple regulators with moderate PSRR values. By changing the parameter from PSRR magnitude to regulator quantity and configuration, the system achieves comparable noise suppression without the need for meticulous calibration or high-PSRR components
Data Source
AI summary
A circuit may comprise a first node, a ring oscillator, a regulator, and a Kvcc compensation circuit. The first node may be a supply node to provide a supply voltage for the circuit. The ring oscillator may be formed from inverters. The regulator may use a single transistor between the first node and a second node for powering the oscillator. The K compensation circuit may be used to provide to the oscillator a variable capacitive load that is dependent on the supply at the first supply node, and it may drag oscillator frequency down when the first node supply goes up.