Edge-Combining Signal Generator for Low-Noise Frequency Multiplication
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Solution Overview
Problem
Low-cost crystal oscillators provide low-frequency oscillating signals, limiting the noise performance of frequency synthesizers, which can be improved by multiplying the reference frequency while preserving the clean properties of the crystal oscillator.
Innovation Solution
A signal generator using multi-sampling and edge combining, comprising multiple edge sampling circuits and an edge combining circuit, which samples rising and falling edges of an oscillating signal to generate an output signal with a higher frequency, reducing in-band noise by combining these edges using logic operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the reference frequency is multiplied to improve noise performance, then the noise performance improves, but the clean crystal oscillator properties may be lost
Solution Approach 1:
The patent segments the frequency multiplication process into multiple independent edge sampling circuits, each sampling at different phases. This segmentation allows the system to achieve higher output frequency while maintaining the clean properties of the original crystal oscillator signal by processing it through multiple clean sampling paths rather than a single complex multiplication path.
Solution Approach 2:
The patent applies preliminary action by performing edge sampling at multiple predetermined phases before combining the results. The sampling circuits are configured with specific phase shifts (e.g., 0°, 60°, 120°, 180°, 240°, 300°) to capture edges at optimal points in the oscillation cycle, ensuring clean sampling occurs before the edges are combined to produce the frequency-multiplied output.
2Speed
If multiple edge sampling circuits are used to increase output frequency, then the frequency multiplication is achieved, but the device complexity increases
Solution Approach 1:
The patent merges the outputs of multiple edge sampling circuits through an edge combining circuit that uses logic operations (such as OR gates) to combine the sampled signals. This combining approach allows the system to achieve frequency multiplication (e.g., 6x or 12x the input frequency) while managing complexity by systematically integrating multiple simple sampling circuits rather than using a single complex frequency multiplier.
3Measurement precision
If sampling phases are optimized to maintain noise performance, then the noise performance is preserved, but the calibration complexity increases
Solution Approach 1:
The patent implements feedback through calibration circuits that monitor the output signal and adjust the sampling phases and voltages to optimize noise performance. The calibration process uses feedback from the actual signal edges to automatically set the correct sampling timing and threshold voltages for each sampling circuit, preserving the clean crystal oscillator properties while achieving frequency multiplication.
Data Source
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AI summary
A signal generator (100, 1100, 1300) generates an output signal (S_OUT) according to an oscillating signal (XO_IN). The signal generator (100, 1100, 1300) has a plurality of edge sampling circuits (102_1-102_N) and an edge combining circuit (104, 600, 800, 1000). Each of the edge sampling circuits (102_1-102_N) receives the oscillating signal (XO_IN), samples the oscillating signal (XO_IN) to obtain at least one of a rising edge and a falling edge in one cycle of the oscillating signal (XO_IN), and outputs a sampled signal (S1-SN) using the at least one of the rising edge and the falling edge. The edge combining circuit (104, 600, 800, 1000) combines a plurality of sampled signals (S1-SN) generated by the edge sampling circuits (102_1-102_N), respectively, to generate the output signal (S_OUT).