External-Resistor Oscillator Leakage Compensation for Frequency Accuracy
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Solution Overview
Problem
Oscillators with on-chip resistor components face accuracy issues due to temperature-dependent non-linear variations and drift over time, which can result in frequency deviations beyond 1% of the target frequency, and the use of external resistors introduces leakage currents that affect accuracy.
Innovation Solution
A pin-leakage compensation system that includes a charging current generator with a current mirror and amplifier coupled to an external resistor, along with leakage circuitry that replicates and adjusts the leakage current to maintain the designed current flow to the oscillator circuitry, thereby compensating for leakage across voltage and temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external resistors are used in oscillators, then frequency accuracy is improved, but leakage currents from the pin affect accuracy
Solution Approach 1:
The patent converts the harmful leakage current into a useful signal by replicating it through a current mirror circuit. The leakage current that would normally degrade accuracy is instead captured and used to generate a compensating current that is injected back into the oscillator circuit, effectively canceling out its harmful effects while maintaining frequency accuracy.
Solution Approach 2:
The patent implements a feedback mechanism where the leakage current is continuously monitored through the current mirror, processed through compensation circuitry, and fed back as a compensating current to the oscillator. This closed-loop feedback system dynamically adjusts for leakage variations across voltage and temperature changes, maintaining stable frequency accuracy.
2Device complexity
If on-chip resistor components are used, then device complexity is reduced, but temperature-dependent non-linear variations cause frequency drift
Solution Approach 1:
The patent extracts the resistor component from the chip and places it externally. This removes the on-chip resistor's temperature-dependent non-linear variations and drift issues, allowing the use of high-precision external resistors that maintain stable values across temperature ranges, thereby improving frequency stability while keeping the overall device relatively simple.
Solution Approach 2:
The patent introduces an intermediary current mirror and compensation circuitry that mediates between the external resistor and the oscillator core. This intermediary structure isolates the oscillator from the external resistor's potential variations and actively compensates for any drift, maintaining frequency stability without requiring complex on-chip resistor designs.
Data Source
AI summary
In an example, a system includes an oscillator circuit on a chip. The oscillator circuit includes a charging current generator including a current mirror and an amplifier, where the amplifier is coupled to a pin on the chip, and where the pin is adapted to be coupled to an external resistor, where the external resistor is external to the chip. The oscillator circuit also includes oscillator circuitry coupled to the charging current generator, where the oscillator circuitry includes a comparator, a phase generator, a first capacitor coupled to a first switch, and a second capacitor coupled to a second switch. The oscillator circuit includes leakage circuitry coupled to the current mirror, where the leakage circuitry is configured to draw a current from the current mirror proportional to a leakage current flowing through the external resistor from circuitry internal to the chip.