Probability Mass Redistribution for Fractional-N Spur Suppression
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Solution Overview
Problem
Fractional-N frequency synthesizers suffer from spurious frequency components in their output spectrum due to interactions between digital modulators and circuit nonlinearities, despite efforts to reduce quantization and additive noise.
Innovation Solution
A probability mass redistributor device is introduced, comprising a mapping block, difference blocks, and a summing block, which modifies the probability mass function of the digital modulator's output to minimize spurious frequencies without impacting noise-shaping spectral properties. This device is placed between the digital modulator and the feedback divider in a fractional-N frequency synthesizer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a digital modulator is used in a fractional-N frequency synthesizer, then the synthesizer can achieve fractional frequency division, but spurious frequency components appear in the output spectrum due to interactions with circuit nonlinearities
Solution Approach 1:
The patent introduces a probability mass redistributor as an intermediary component between the digital modulator and the feedback divider. This redistributor modifies the probability distribution of the modulator output before it interacts with the nonlinear feedback path, thereby reducing the generation of spurious frequency components while preserving the fractional frequency division capability.
Solution Approach 2:
The patent changes the probability mass distribution parameter of the digital modulator output by applying a redistributor function. This parameter transformation alters the statistical characteristics of the signal, reducing the interaction with circuit nonlinearities that produce spurs, while maintaining the essential fractional-N synthesis function.
2Manufacturing precision
If conventional digital modulators are used to reduce quantization noise, then additive noise is reduced, but spurious frequency components still persist in the output spectrum
Solution Approach 1:
The probability mass redistributor serves as an intermediary that addresses the remaining spurious components after conventional quantization noise reduction. It specifically targets the interaction between the modulator output and circuit nonlinearities, which is a separate mechanism from quantization noise, thereby resolving the persistent spur issue without compromising the noise reduction already achieved.
Solution Approach 2:
The patent applies a parameter transformation to the probability mass function of the modulator output. This change in distribution parameters specifically addresses the spurious component generation mechanism that remains after quantization noise reduction, allowing simultaneous achievement of low noise and low spurs.
Data Source
AI summary
The present invention provides a probability mass redistributor device comprising an input port and an output port. The device comprises a mapping block configured to perform a selected mapping function from a plurality of mapping functions on a random bitstream to generate an output signal having a desired probability mass function, at least one difference block, wherein the input to the at least one difference block comprises the output from the mapping block, and the output of the at least one difference block produces a modulation term, and wherein the output of each difference block is the difference between a previous value of the input signal to the block and a current value of the input signal to the block, and a summing block for summing a signal received by the input port and the modulation term to form an output signal.