Crystal Oscillator Compensation Using a Programmable PLL Divider
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Solution Overview
Problem
Crystal oscillators used in phase-locked loops experience frequency variation due to temperature changes, which existing compensation methods, such as temperature-compensated crystal oscillators and voltage-controlled crystal oscillators, fail to adequately address, especially outside standard temperature ranges, and their hardwired compensation circuitry does not adjust for aging hardware.
Innovation Solution
A programmable frequency divider is configured in the feedback path of a phase-locked-loop with device parameters based on frequency offset compensation, determined by a compensation circuitry that calculates the inverse of the frequency error associated with the crystal oscillator's temperature, using a look-up table or s-curve fit-function to adjust the frequency divider settings and maintain frequency stability across a wide temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If temperature-compensated crystal oscillators or voltage-controlled crystal oscillators are used, then frequency stability is improved within standard temperature ranges, but frequency variation occurs outside these ranges and hardwired compensation circuitry cannot adjust for aging hardware
Solution Approach 1:
The patent implements a dynamically reconfigurable frequency compensation system using a programmable frequency divider controlled by a lookup table that stores compensation values for different temperature ranges. Unlike fixed hardwired compensation, this system can be reprogrammed to adapt to changing temperature conditions and hardware aging, allowing the compensation parameters to be updated without physical circuit changes. The programmable divider ratio is adjusted based on temperature sensor input and lookup table data, enabling continuous adaptation across extended temperature ranges.
Solution Approach 2:
The system changes the compensation parameter (frequency divider ratio) based on temperature conditions and aging characteristics. A lookup table stores pre-calculated compensation values for different temperature ranges and aging periods. The system selects appropriate compensation parameters dynamically based on sensor input, allowing the same hardware to provide optimized compensation for various operating conditions without requiring physical reconfiguration of the compensation circuitry.
2Reliability
If conventional temperature compensation methods are used, then frequency error is reduced within operating temperature ranges, but additional costly circuitry and precise manufacturing are required
Solution Approach 1:
The patent uses a lookup table that stores pre-calculated compensation values derived from characterized frequency error data. Instead of implementing complex real-time calculation circuitry, the system copies pre-computed compensation parameters from the lookup table based on temperature sensor input. This approach transfers the computational complexity from the operating system to the manufacturing/characterization phase, where frequency error data is measured and stored in the lookup table during device production or initial operation.
Solution Approach 2:
The system replaces analog hardwired compensation circuitry with a digital implementation using a programmable frequency divider and lookup table. This substitution allows for more flexible and precise compensation by using digital logic and stored data rather than fixed analog circuit parameters. The digital approach enables easier reconfiguration and updating of compensation parameters without requiring precise analog component matching or complex analog circuit design.
Data Source
AI summary
Systems, methods, and devices of the present disclosure relate, generally, to compensating for frequency error of a reference signal supplied to a clock-tracking-loop due to temperature. Error characteristics of a crystal oscillator that supplies the reference signal are used to compensate for possible frequency errors. Other systems, methods and devices are disclosed.