PLL Comb-Feedback Circuit for Midband Phase Noise Reduction
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Solution Overview
Problem
High-frequency signal generators experience degraded spurious performance when frequency is multiplied, affecting system performance.
Innovation Solution
A signal generator design incorporating a voltage controlled oscillator, nonlinear transmission line comb generator, bandpass filter, direct digital synthesizer, phase and frequency detector, and lowpass filter, which selects and compares tones to feedback control the oscillator, reducing phase noise and spurious levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If frequency multiplication is used in high-frequency signal generators, then the operating frequency range is extended, but spurious performance degrades by a factor of 20*Log(N)
Solution Approach 1:
The patent implements a feedback mechanism where the output of the comb generator is fed back through a frequency divider and phase detector to the VCO control input. This feedback loop continuously monitors and corrects frequency deviations and spurious components, maintaining signal purity even at high multiplication factors N=16-64.
Solution Approach 2:
The patent introduces a comb generator as an intermediary device between the VCO and the output. This comb generator creates a spectrum of frequencies that are then filtered and fed back, allowing selective reinforcement of the fundamental frequency while suppressing spurious components generated during multiplication.
2Speed
If frequency multiplication factor N is increased to achieve higher output frequencies, then the signal generator can operate at higher frequencies, but phase noise increases
Solution Approach 1:
The feedback loop including the phase detector continuously monitors phase deviations and corrects them by adjusting the VCO control voltage. This active correction suppresses phase noise accumulation that would otherwise occur during frequency multiplication by factors of 16-64.
Solution Approach 2:
The comb generator pre-establishes a spectrum of frequencies with defined phase relationships before multiplication occurs. This preliminary structure allows the feedback system to work more effectively, as the phase relationships are already established and can be maintained through the multiplication process.
Data Source
AI summary
A signal generator. A voltage controlled oscillator generates a signal that is fed to a comb generator, e.g., a nonlinear transmission line. A tone, from among a comb of tones at the output of the comb generator, is selected by a bandpass filter, its frequency is divided, e.g., by a direct digital synthesizer, and the result is compared, e.g., by a phase and frequency detector that receives a reference signal at its other input. The output of the phase and frequency detector is fed back, e.g., through a lowpass filter, to the voltage controlled oscillator.