Differential Ring Oscillator Supply Segmentation for Jitter Control
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Solution Overview
Problem
Voltage-controlled oscillators (VCOs) in phase-locked loops are highly susceptible to generating jitter in output signals due to supply voltage noise, particularly at high frequencies, which affects their performance and stability.
Innovation Solution
The implementation of differential variable delay circuits forming a ring oscillator with a constant supply voltage provided to some transistors and a variable supply voltage to others, along with a phase-locked loop circuit that includes phase detection, voltage buffering, and low pass filtering, helps reduce jitter by maintaining a constant supply voltage and minimizing the impact of noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a voltage-controlled oscillator uses a variable supply voltage to control frequency, then the frequency tuning range is improved, but the oscillator becomes highly susceptible to supply voltage noise and generates jitter in output signals
Solution Approach 1:
The oscillator circuit is divided into two separate transistor groups: a first group (transistors 501-504) receiving the variable oscillator supply voltage VOS for frequency control, and a second group (transistors 505-508) receiving a constant supply voltage VCC for noise reduction. This segmentation allows independent optimization of each group's function.
Solution Approach 2:
Different supply voltage characteristics are applied to different parts of the circuit: the variable supply voltage VOS is applied locally to the frequency-control transistors (501-504) to enable tuning, while a constant, noise-free supply voltage VCC is applied locally to the buffer transistors (505-508) to maintain signal stability and reduce jitter.
2Speed
If the oscillator supply voltage varies to adjust frequency, then the frequency response is improved, but the gain varies significantly across the tuning range increasing noise susceptibility
Solution Approach 1:
The circuit segments transistor functions: transistors 501-504 handle frequency control with variable voltage, while transistors 505-508 handle signal buffering with constant voltage, isolating the noise-sensitive buffering function from voltage variations.
Solution Approach 2:
The constant supply voltage VCC is applied specifically to the buffer transistor sources to create a noise-immune region, while the variable voltage VOS is confined to the frequency-control transistors, localizing the effect of voltage variations.
3Adaptability or versatility
If differential variable delay circuits are used to form a ring oscillator, then the frequency tuning capability is improved, but the circuit becomes more complex with multiple transistors requiring multiple supply voltages
Solution Approach 1:
The constant supply voltage VCC serves multiple functions: it powers the buffer transistors (505-508) and provides a stable reference for the entire oscillator circuit, reducing the need for additional voltage generation circuits.
Solution Approach 2:
The differential variable delay circuits are segmented into frequency-control elements (transistors 501-504) and buffer elements (transistors 505-508), with each segment receiving appropriate supply voltage to optimize its specific function.
Data Source
AI summary
An oscillator circuit includes differential variable delay circuits coupled together to form a ring oscillator. Each of the differential variable delay circuits has first and second inputs and first, second, third, and fourth transistors. A constant supply voltage is provided to sources of the first and the second transistors in each of the differential variable delay circuits. A variable supply voltage is provided to sources of the third and the fourth transistors in each of the differential variable delay circuits. Gates of the first and the third transistors are coupled to the first input. Gates of the second and the fourth transistors are coupled to the second input. The oscillator circuit generates a periodic output signal having a frequency that varies based on changes in the variable supply voltage.