PLL Non-Integer Ratio Measurement Using Time-Difference Circuits
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Solution Overview
Problem
Conventional systems fail to precisely determine a non-integer ratio between two signals due to the fractional part of the ratio, and existing methods are costly in terms of surface area and power consumption.
Innovation Solution
A method and device that determine the integer and fractional parts of the ratio between two signals, generating a digital word representative of the non-integer ratio, using a phase-locked loop circuit with a comparator, digitally-controlled oscillator, and calculation circuits to adjust the frequency of the output signal based on the error between the determined and target ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional systems are used to determine the ratio between two signals, then the system structure is simple, but the measurement precision of the non-integer ratio is insufficient due to the fractional part
Solution Approach 1:
The patent segments the non-integer ratio determination into two independent parts: an integer part determined by a division circuit and a fractional part determined by a time difference measurement circuit. This segmentation allows each part to be processed separately with appropriate circuitry, achieving precise measurement of the complete non-integer ratio without requiring an overly complex unified system.
2Measurement precision
If direct determination of non-integer ratio is implemented, then measurement precision is improved, but power consumption and surface area increase
Solution Approach 1:
The patent replaces complex frequency synthesis mechanisms with a simpler time domain measurement approach. Instead of using traditional frequency synthesis circuits to handle the fractional part, the invention uses a time difference measurement circuit that directly measures the time offset between signal edges, converting a frequency-domain problem into a time-domain measurement that consumes less power and occupies less area.
3Measurement precision
If frequency synthesis is performed before determining the ratio, then the non-integer ratio can be determined, but additional components are required increasing surface area and power consumption
Solution Approach 1:
The patent extracts the fractional part determination from the traditional frequency synthesis process and handles it separately through time difference measurement. By taking out the fractional part processing from the main frequency synthesis path, the invention eliminates the need for additional frequency synthesis components, reducing both surface area and power consumption while maintaining measurement precision.
4Measurement precision
If over-sampling of variable frequency signals is used, then the non-integer ratio can be calculated from phase shifts, but the method is complex and not compatible with digital processing for noise elimination
Solution Approach 1:
The patent substitutes complex over-sampling and phase shift analysis with a direct time difference measurement approach. By measuring the time offset between corresponding edges of the reference signal and the divided signal directly in the time domain, the invention simplifies the processing architecture and produces a digital word representation that is naturally compatible with digital filtering and noise elimination techniques.
Data Source
AI summary
A phase-locked loop circuit having a comparator that receives a target digital word representative of a non-integer target ratio between a main signal and a reference signal having a reference frequency. The circuit also includes digitally-controlled oscillator coupled to the comparator to deliver an output signal. One return loop is coupled between the output of the oscillator and the comparator. The latter includes a device to generate a digital word representing the non-integer ratio between the period of the reference signal and the period of the output signal, the reference signal and the output signal respectively corresponding to the first and second signal, and the fixed integer part N being equal to the integer part of the target non-integer ratio. The comparator compares the digital word and target digital word. The oscillator adjusts the frequency of the output signal as a function of the result delivered by the comparator.