Feedback Ring VCO Topology for Wide Tuning and Constant Swing
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Solution Overview
Problem
Conventional voltage controlled oscillators (VCOs) have limited tuning range and variable voltage swing, making them unsuitable for applications requiring wide frequency adjustment and stable signal amplitude, while existing architectures like the feed-forward ring oscillator suffer from restricted tuning range and decreased signal swing with increased frequency.
Innovation Solution
A Feedback multipass Ring Oscillator topology is introduced, featuring feedback connections that allow for a wider tuning range with a substantially constant voltage swing, achieved by adjusting the mix of feedback and primary inputs within each amplifier stage using a control voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional VCO or feed-forward ring oscillator is used, then the circuit is simple to implement, but the tuning range is limited and voltage swing varies with frequency
Solution Approach 1:
The patent introduces feedback connections from later stages back to earlier stages in the ring oscillator. This feedback mechanism allows the circuit to maintain stable operation across a wide tuning range while keeping the voltage swing constant. The feedback paths include adjustable mixing circuits that combine feedback signals with primary stage inputs, enabling precise control of the oscillation characteristics without requiring complex external control circuits.
Solution Approach 2:
The ring oscillator is divided into multiple independent amplifier stages, each with its own feedback mixing circuit. This segmentation allows each stage to be optimized independently for wide tuning range operation while maintaining overall system stability. Each stage can adjust its feedback ratio separately, enabling fine-grained control over the frequency response and voltage swing characteristics across the entire tuning range.
2Reliability
If feed-forward ring oscillator is used, then the circuit structure is simple, but the voltage swing decreases with increased frequency
Solution Approach 1:
Feedback connections are established from outputs of later amplifier stages back to inputs of earlier stages. Each feedback path includes a mixing circuit that combines the feedback signal with the primary stage input. This feedback mechanism compensates for the natural decrease in voltage swing at higher frequencies by injecting additional signal energy from later stages, thereby maintaining constant voltage swing across the entire tuning range while enabling wide frequency adjustment.
Solution Approach 2:
The patent employs variable gain control in the feedback mixing circuits, allowing the feedback ratio to be adjusted as a function of frequency. By dynamically changing the feedback parameter (mixing ratio) based on the operating frequency, the system maintains constant voltage swing across the tuning range. This parameter adjustment is achieved through control voltages that modify the mixing circuit characteristics in response to frequency changes.
3Adaptability or versatility
If conventional VCO architectures are used, then the design is straightforward, but the tuning range remains limited
Solution Approach 1:
The oscillator is segmented into multiple identical or similar amplifier stages, each contributing to the overall frequency determination. This segmentation allows the tuning range to be extended by adjusting the delay of individual stages independently. The modular structure makes the design more manageable despite the increased complexity, as each stage can be designed and tuned separately using standard techniques.
Solution Approach 2:
Multiple feedback paths are implemented, with each path connecting a later stage back to an earlier stage. These feedback connections provide additional degrees of freedom for frequency control and enable the system to achieve wide tuning range operation. The feedback mechanism also improves the linearity of the frequency-control characteristic, making the VCO easier to operate over its extended tuning range.
Data Source
AI summary
A wide tuning range and constant swing VCO is described that is based on a multipass Ring Oscillator enhanced with feed-backward connections. This VCO is designed to overcome tuning range limitations of prior-art “feed-forward” ring oscillators. The Feedback multipass Ring Oscillator of the invention provides decreasing frequency when tuned by increasing the feedback, thus covering a much wider tuning range irrespective of the speed limit of the technology while at the same time providing almost constant amplitude.