Sine-to-Square Converter Threshold Control for Lower Phase Noise
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Solution Overview
Problem
Low frequency additive noise from oscillator biasing circuitry and sine-to-square wave converters is converted to phase noise, affecting the performance of frequency synthesizers and data communication links.
Innovation Solution
A sine-to-square wave converter circuit with a clock multiplier and duty cycle correction circuit that adjusts the threshold based on pulse width differences, using a 2× clock multiplier to move additive noise to odd harmonics and a feedback loop to correct duty cycle, reducing phase noise and improving communication link performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a sine-to-square wave converter is used to provide a rectangular wave reference input to the frequency synthesizer, then the synthesizer is less susceptible to noise sources from the synthesizer circuit, but low frequency additive noise from the oscillator or converter gets converted to phase noise at the output
Solution Approach 1:
The patent implements a feedback mechanism where the output of the frequency synthesizer is fed back through a divider to the phase detector, which compares it with the square wave reference. This feedback loop allows the system to detect and correct phase deviations caused by additive noise, thereby reducing phase noise at the output while maintaining the benefits of the rectangular wave reference
Solution Approach 2:
The patent introduces a phase detector as an intermediary component between the square wave reference and the voltage controlled oscillator. This phase detector mediates the interaction by comparing phases and generating error signals that drive the feedback loop, effectively separating the reference function from the oscillation function and preventing direct noise transfer
2Reliability
If the threshold of the sine to square wave converter is adjusted to correct duty cycle, then phase noise performance is improved, but additional circuit complexity is introduced
Solution Approach 1:
The patent combines the duty cycle correction function with the existing feedback loop components. The threshold adjustment mechanism is integrated into the phase detector and feedback path, allowing duty cycle correction to be achieved using the same feedback infrastructure already present for phase noise reduction, thereby minimizing additional circuit complexity
Solution Approach 2:
The feedback loop and phase detector are designed to perform multiple functions: they simultaneously maintain phase synchronization, correct duty cycle variations, and reduce phase noise. This multi-functionality eliminates the need for separate dedicated circuits for each function, reducing overall system complexity while achieving multiple goals
Data Source
AI summary
A sine to square wave converter circuit receives a sine wave signal and supplies a first square wave signal having a first frequency. A 2× clock multiplier circuit multiplies the first square wave signal and supplies a second square wave signal with a second frequency that is twice the first frequency. A first storage element that is clocked by the second square wave signal stores a delayed version of the first square wave signal and supplies an even-odd signal. A second storage element that is clocked by the second square wave signal receives the even-odd signal and supplies an odd-even signal. A duty cycle correction circuit adjusts the threshold of the sine to square wave converter based on a difference in duty pulse widths between the even-odd signal and the odd-even signal.