PLL Signal Generator Calibration Using Shared Capacitor Error
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Solution Overview
Problem
Signal generators with phase-locked loops experience long calibration and settling times due to process, voltage, and temperature variations affecting capacitor values, leading to inefficient frequency control.
Innovation Solution
A method that calculates and compensates for systematic capacitance errors in capacitors using the frequency lock and switching state, allowing for calibration of oscillator control subsystems to adjust for PVT variations, thereby improving the settling characteristics of the phase-locked loop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional capacitor-based frequency control is used in phase-locked loops, then the signal generator can operate across process, voltage, and temperature variations, but the calibration time and settling time become excessively long due to capacitor value deviations from nominal values
Solution Approach 1:
The patent performs preliminary characterization of capacitor values across process, voltage, and temperature corners during manufacturing. This pre-acquired data is stored and used during operation to predict actual capacitor values under current PVT conditions, eliminating the need for long calibration times while maintaining accurate frequency control
Solution Approach 2:
The system uses feedback from the characterized capacitor data to continuously adjust frequency control decisions. By monitoring actual capacitor values (retrieved from characterization data based on current PVT conditions) and comparing them to nominal values, the system compensates for deviations in real-time, maintaining reliability without extended settling periods
2Measurement precision
If capacitor values are adjusted to compensate for PVT variations, then frequency accuracy improves, but the complexity of the control system increases due to additional calibration mechanisms
Solution Approach 1:
Capacitor characterization data across various PVT corners is pre-measured and stored in lookup tables during manufacturing. During operation, the system simply retrieves the appropriate pre-characterized values based on current sensors readings, avoiding complex real-time calculations while maintaining high frequency accuracy
Solution Approach 2:
The patent replaces complex mechanical adjustment mechanisms with a digital lookup table approach. Instead of physically adjusting capacitors or using complex analog calibration circuits, the system uses pre-stored characterization data and digital processing to achieve accurate frequency control, significantly reducing hardware complexity
Data Source
AI summary
A signal generator comprises (i) a first set of capacitors at least partially switchably connectable for adjusting a frequency of an oscillator as part of a phase-locked loop and (ii) a second set of capacitors comprised in one or more oscillator control subsystems. A method of controlling the signal generator comprises: (i) acquiring a frequency lock in the phase-locked loop, (ii) calculating, in conjunction with the acquiring of the frequency lock, a systematic capacitance error of the first set of capacitors due to process, voltage, and temperature variations based on the frequency of the oscillator and a switching state of the first set of capacitors, and (iii) calibrating the one or more oscillator control subsystems using the systematic capacitance error, thereby compensating for process, voltage, and temperature variations common between the first set of capacitors and the second set of capacitors.