Mutual-Injection Ring Oscillators for High-Frequency Multi-Phase Clocks
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Solution Overview
Problem
Ring oscillator-based multi-phase clock generation circuits are limited by an inverse relationship between the number of phases and the frequency of signals they can produce, restricting their capability to generate multiple phases at high frequencies.
Innovation Solution
A two-stage clock generation circuit utilizing mutual injection between two N-stage ring oscillators, each with series-coupled delay elements and parallel shunt circuits, allowing for independent control of phase and frequency, generating 2N clock signals in 2N phases that are substantially evenly spaced.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional ring oscillator-based multi-phase clock generation circuits are used, then the number of phases can be increased, but the frequency of signals produced decreases
Solution Approach 1:
The circuit is divided into two separate N-stage ring oscillators instead of using a single 2N-stage ring oscillator. Each ring oscillator generates N phases, and through mutual injection coupling between the two oscillators, a total of 2N phases are achieved. This segmentation allows each oscillator to operate at higher frequencies while still producing the desired number of phases.
Solution Approach 2:
The outputs of two separate ring oscillators are combined through mutual injection coupling, where the output of each oscillator is fed back to the input of the other. This merging approach enables the generation of 2N phases by combining the phase outputs from both oscillators, achieving high-frequency multi-phase generation that would not be possible with a single oscillator.
2Adaptability or versatility
If the number of delay elements is increased to generate more phases, then more phases are produced, but the circuit complexity and area increase
Solution Approach 1:
Each ring oscillator is designed as a universal phase generation unit that can produce N phases. By using two identical modular units with mutual injection coupling, the circuit achieves 2N phases without designing a completely different architecture. This multi-functional approach allows the same circuit block to serve multiple phase generation purposes.
Solution Approach 2:
The phase generation function is segmented into two identical N-stage ring oscillators rather than using a single large 2N-stage oscillator. This segmentation reduces the complexity of individual oscillator stages and allows for modular design, where each module can be independently optimized and replicated.
3Adaptability or versatility
If more delay elements are added to achieve higher phase counts, then more phases are generated, but the oscillation frequency decreases
Solution Approach 1:
The total phase generation requirement is segmented into two separate oscillators, each handling N phases. This segmentation ensures that each oscillator has a manageable number of delay elements, maintaining higher oscillation frequencies compared to a single 2N-stage oscillator which would have excessive total delay.
Solution Approach 2:
The frequency and phase outputs from two separate oscillators are merged through mutual injection coupling. This merging allows the system to achieve 2N phases at high frequencies by combining the outputs of two frequency-optimized oscillators rather than forcing a single oscillator to generate all 2N phases.
Data Source
AI summary
A multi-stage clock generation circuit is disclosed. The circuit includes first and second ring oscillators. The ring oscillators include a corresponding plurality of delay elements coupled in series, with a plurality of shunt circuits in parallel with corresponding inverters. The shunt circuits include respective interpolation nodes, which are resistively coupled to input and output nodes of their corresponding inverters. The interpolation nodes of the first ring oscillator are coupled to delay element input and output nodes of the second ring oscillator. Similarly, the interpolation nodes of the second ring oscillator are coupled to delay element input and output nodes of the first ring oscillator.