Dual Crystal DPLL Clock Circuit for Temperature-Stable Frequency
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Solution Overview
Problem
Existing circuit applications require stable frequency and low jitter characteristics, but the high cost of temperature-compensated crystal oscillators (TCXO) and oven-controlled crystal oscillators (OCXO) makes them impractical for widespread use, necessitating a cost-effective alternative for generating temperature-stable clocks.
Innovation Solution
A circuit and method utilizing two ordinary crystal oscillators in a single package, with a phase acquisition circuit, digital phase locked loops, and a crystal oscillator variation estimator, along with a synthesizer, to achieve temperature stability and low jitter by characterizing frequency variations over temperature and compensating for frequency drift using polynomial coefficients stored in memory.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If temperature-compensated crystal oscillators (TCXO) or oven-controlled crystal oscillators (OCXO) are used, then frequency stability and temperature stability are improved, but cost increases significantly
Solution Approach 1:
The patent uses a low-cost ordinary crystal oscillator as a copy/alternative to expensive TCXO or OCXO solutions. By implementing digital compensation techniques, the system achieves temperature stability without requiring the expensive hardware mechanisms (temperature sensors, compensation circuits, ovens) found in traditional solutions, thereby copying the functional outcome at lower cost
Solution Approach 2:
The patent changes the operating parameters of ordinary crystal oscillators through digital control. By measuring temperature and applying compensation algorithms that adjust the oscillator frequency based on temperature characteristics, the system achieves temperature stability without the physical temperature control mechanisms of TCXO/OCXO, resolving the cost-stability contradiction
2Ease of manufacture
If ordinary crystal oscillators are used, then cost is reduced, but frequency stability and temperature stability deteriorate
Solution Approach 1:
The patent implements a feedback mechanism where the ordinary crystal oscillator's output is monitored, temperature is measured, and compensation is applied based on the measured deviations. The system continuously adjusts the oscillator frequency based on feedback from temperature sensors and frequency detectors, enabling ordinary oscillators to achieve stability levels previously only available from expensive compensated oscillators
Solution Approach 2:
The patent performs preliminary characterization of the crystal oscillator's temperature-frequency characteristics during manufacturing. By pre-storing compensation data and calibration information in memory, the system prepares the ordinary oscillator in advance to compensate for temperature drift, achieving stability without requiring expensive real-time compensation hardware
Data Source
AI summary
A circuit for generating temperature-stable clocks including first and second crystal oscillators, an input for a reference clock source, a clock output, a first phase acquisition circuit coupled to the first and second crystal oscillators, a second phase acquisition circuit coupled to the input for the reference clock source and to the second crystal oscillator, a first DPLL coupled to the first phase acquisition circuit, a crystal oscillator variation estimator coupled to the first DPLL, a second DPLL coupled to the second phase acquisition circuit and including a phase-frequency detector having a input coupled to the second phase acquisition circuit, a loop filter, a frequency subtractor having an input coupled to the loop filter and an input coupled to the crystal oscillator variation estimator, and a DCO coupled to the frequency subtractor and driving an input of the phase-frequency detector.