Microwave Frequency Synthesizer Loop Accumulation Spur Suppression
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Solution Overview
Problem
Microwave frequency synthesizers face challenges in achieving low phase noise, fine frequency resolution, and fast switching speed while maintaining low cost, small size, and low power consumption, as existing architectures either result in costly, bulky, and power-hungry solutions or require complex multi-loop phase-locked loop systems that compromise performance.
Innovation Solution
A frequency synthesizer using a single phase lock loop with a feedback accumulator and a variable reference generator, where the feedback accumulation rate is derived from a first seed word and the variable reference frequency is derived from a second seed word, incorporating a spur suppressor for arithmetic frequency conversions to manage spurious signal levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single phase-locked loop architecture is used, then device complexity, cost, size and power consumption are reduced, but phase noise performance and frequency resolution deteriorate
Solution Approach 1:
The feedback path is segmented into two independent components: a feedback accumulator that provides fine frequency resolution through digital accumulation, and a phase detector that maintains phase noise performance. This segmentation allows each component to be optimized independently, achieving both low phase noise and fine frequency resolution with a single loop architecture.
Solution Approach 2:
A feedback accumulator is introduced as an intermediary component between the voltage-controlled oscillator and the phase detector. This accumulator performs digital frequency synthesis by accumulating phase error signals, providing fine frequency resolution without requiring multiple phase-locked loops, thereby maintaining system simplicity while improving performance.
2Reliability
If a high reference frequency is used, then phase noise is reduced, but frequency resolution deteriorates
Solution Approach 1:
The system transitions from a single-dimensional frequency control approach to a two-dimensional approach by separating frequency resolution (achieved through digital accumulation in the feedback path) from phase noise control (achieved through the reference frequency). This dimensional separation allows independent optimization of both parameters.
Solution Approach 2:
The patent replaces the traditional mechanical/approach of using multiple loops or narrow bandwidth filters with a digital feedback accumulator that performs frequency synthesis through numerical accumulation. This digital substitution enables fine frequency resolution without compromising phase noise performance.
3Object-generated harmful factors
If narrow phase-locked loops are used to prevent spurious signal sidebands, then spurious signal levels are reduced, but switching speed deteriorates
Solution Approach 1:
The feedback accumulator continuously accumulates phase error signals and adjusts the oscillator frequency in real-time, providing rapid frequency switching capability. This feedback mechanism suppresses spurious signals through continuous correction without requiring narrow loop bandwidth, thereby maintaining fast switching speed.
Data Source
AI summary
A frequency synthesizer and a method for synthesizing a microwave output signal frequency. The synthesizer uses a reference signal having a variable frequency and accumulation in feedback of a phase locked loop for synthesizing a microwave output frequency. The feedback accumulation rate is derived from a first seed word and the variable reference frequency is derived from a second seed word. A spur suppressor having arithmetic frequency conversions reduces the levels of in-band spurious signals of the variable reference frequency signal in order to reduce the spurious signal levels in the output signal.