RC Oscillator Capacitor Trimming for High-Temperature Stability
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Solution Overview
Problem
Low-power RC relaxation oscillators used in applications like real-time clocks face frequency variations across temperatures due to high drain/source and gate oxide leakages from trimming switches, compromising stability and accuracy.
Innovation Solution
The method involves varying the capacitor ratio in the RC relaxation oscillator to modulate its frequency, reducing the impact of leakages associated with trimming switches by selectively toggling switching elements in the capacitor network, thereby adjusting the RC delay constant.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If trimming switches are used to adjust frequency in low-power RC oscillators, then frequency accuracy can be improved, but drain/source and gate oxide leakages increase at high temperatures, worsening frequency stability
Solution Approach 1:
The patent extracts the harmful trimming switches from the oscillator circuit entirely. Instead of using traditional trimming switches that cause leakage, the invention uses a capacitor ratio adjustment mechanism that eliminates the need for switches in the frequency trimming path, thereby removing the source of temperature-dependent leakages while preserving frequency accuracy.
Solution Approach 2:
The patent changes the trimming parameter from resistance-based (using trimming switches) to capacitance ratio-based. By adjusting the ratio of capacitors in the RC network rather than using switching elements, the system achieves frequency accuracy without introducing the leakage problems associated with traditional trimming switches at high temperatures.
2Reliability
If capacitor ratio is varied to modulate frequency, then frequency stability across temperatures is improved, but device complexity increases due to additional capacitor networks
Solution Approach 1:
The capacitor network serves multiple functions: it provides the timing function for oscillation, enables frequency trimming through ratio adjustment, and compensates for temperature effects. By making the capacitor network multi-functional, the patent avoids adding separate components for each function, thereby limiting the increase in device complexity while achieving frequency stability.
3Ease of manufacture
If traditional trimming switches are used for frequency adjustment, then manufacturing is simpler, but frequency deviations increase across temperature ranges
Solution Approach 1:
The patent removes trimming switches from the circuit entirely, replacing them with a capacitor ratio adjustment mechanism. This extraction eliminates the manufacturing complexity and reliability issues associated with switches while maintaining ease of fabrication through standard capacitor arrays and switching elements that are well-suited for integrated circuit manufacturing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces frequency deviations across temperatures, enhancing the stability and accuracy of the oscillator's output frequency, particularly in low-power applications.
Implementation Method 1
A relaxation oscillator is a repeating circuit that achieves a repetitive output signal by charging and discharging a capacitor through a resistor. The time that it takes to charge and discharge the capacitor defines a period of the output signal of the relaxation oscillator.
Data Source
AI summary
In some embodiments, the present disclosure relates to a frequency generator having a resistor network and a capacitor network. The capacitor network has a plurality of capacitors connected in parallel with one another. A comparator is configured to output an oscillating voltage signal. An input of the comparator is connected to the output of the resistor network and the output of the capacitor network. A frequency testing circuit is configured to calculate a frequency of the oscillating voltage signal and determine whether the frequency is within a range of an expected frequency. The frequency testing circuit may also be configured to selectively connect a first plate of the plurality of capacitors to a non-varying voltage or to the input of the capacitor network to adjust a frequency of the oscillating voltage signal.