Digitally Controlled Oscillator Drift Compensation With Capacitor Arrays
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Solution Overview
Problem
Existing digital oscillators face challenges in efficiently compensating for frequency drift caused by temperature and aging effects, particularly due to the high cost of analog closed-loop approaches and increased logic power consumption in digitally controlled oscillators without compensation.
Innovation Solution
An all-digital phase locked loop system incorporating a compensation capacitor array and sensing logic, which automatically detects and adjusts capacitance in fine-tuning and compensation capacitor arrays to re-center the frequency, using a digital domain approach that includes a drift sensing and decision-making circuit to correct for temperature and aging-induced drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If temperature sensing and compensation circuits (PTAT circuit or on-die temperature sensors) are used to compensate for temperature drift, then temperature compensation is achieved, but the implementation requires careful device characterization and post-silicon trimming, increasing device complexity and manufacturing cost
Solution Approach 1:
The patent implements a closed-loop feedback mechanism where the control voltage of the oscillator is continuously monitored. When the control voltage deviates from the preset operating point, an error signal is generated and fed back to adjust the common-mode inputs of the varactor, automatically forcing the control voltage back to the preset value. This eliminates the need for open-loop temperature sensing and post-silicon trimming.
Solution Approach 2:
The system uses the oscillator's own control voltage as the sensing parameter for compensation. By monitoring the control voltage directly and using it to drive the compensation mechanism, the system performs self-diagnosis and self-correction without requiring external temperature sensors or complex characterization procedures.
2Reliability
If analog closed-loop approach is used to detect control voltage and feed back error signal to adjust varactor common-mode inputs, then frequency drift compensation is achieved, but the implementation is costly due to analog circuit requirements
Solution Approach 1:
The patent replaces the analog closed-loop mechanism with a digital implementation. Instead of using analog error signal generation and analog varactor control, the system uses digital detection of the control voltage, digital error signal processing, and digital control of the varactor common-mode inputs. This substitution reduces the complexity and cost associated with precision analog circuits while maintaining the effectiveness of the closed-loop compensation.
3Device complexity
If no compensation is provided and fine-tuning curve coverage range is simply extended, then device complexity is reduced, but logic power consumption increases due to longer fine-tuning word length in digitally controlled oscillator
Solution Approach 1:
The patent segments the frequency tuning function into two distinct parts: fine-tuning and compensation. The fine-tuning function handles small adjustments around the operating point with a shorter word length, while the compensation function handles larger drift corrections separately. This segmentation allows the fine-tuning logic to operate with reduced word length, thereby reducing power consumption while maintaining the ability to cover the required frequency range through coordinated operation of both functions.
Data Source
AI summary
Automatic digital sensing and compensation of frequency drift caused by temperature, aging, and/or other effects may be provided by including a compensation capacitor array and a sensing logic. The sensing logic may be configured to detect a drift in a first control signal and to provide the compensation capacitor array with a second control signal. The second control signal is configured to cause an adjustment of capacitance in the compensation capacitor array based on the detected drift in the first control signal.