Relaxation Oscillator Switching to Reduce Aging Frequency Drift
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Solution Overview
Problem
Relaxation oscillators experience frequency degradation due to aging effects, particularly channel hot carrier injection (CHC) and operating point mismatch between current/voltage generator and current mirror transistors, which existing technologies fail to adequately address.
Innovation Solution
The relaxation oscillator employs a switching method where the roles of transistors in the current/voltage generator and current mirror are periodically swapped using the output/clock signal, controlled by controllable switches, to reduce the mismatch and thereby decrease frequency degradation caused by CHC effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If a relaxation oscillator operates continuously, then it provides continuous clock signal output, but frequency degradation occurs due to channel hot carrier injection and aging effects
Solution Approach 1:
The patent implements periodic swapping of transistor roles in the current mirror circuit using the output clock signal itself. The switching transistors periodically exchange positions, creating a periodic action that counteracts the cumulative aging effects. This periodic swapping resets the stress distribution on transistors, preventing continuous degradation of frequency stability while maintaining continuous oscillator operation.
2Device complexity
If transistors in current mirror are kept in fixed positions, then circuit structure is simple, but operating point mismatch causes frequency degradation
Solution Approach 1:
The patent introduces dynamic switching of transistor positions in the current mirror circuit. Instead of fixed transistor positions, the circuit uses switching transistors that periodically change positions based on the clock signal. This dynamic reconfiguration balances the operating points of transistors over time, reducing mismatch-induced frequency errors while adding only moderate circuit complexity through the switching mechanism.
3Measurement precision
If comparator offset degradation is addressed by switching input nodes, then frequency change from comparator offset is cancelled, but operating point mismatch between transistors remains uncanceled
Solution Approach 1:
The patent converts the harmful effect of transistor aging and mismatch into a beneficial self-correcting mechanism. By periodically swapping transistor positions, the circuit ensures that each transistor experiences both high and low stress conditions over time. This transforms the cumulative harmful effect into a balanced average, where the mismatch degradation cancels itself out over complete swap cycles, improving frequency accuracy without additional compensation circuits.
Data Source
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AI summary
A relaxation oscillator with an aging effect reduction technique comprises a comparator (CP) coupled with its input side (CP1, CP2) to a network comprising at least one capacitor (C, C1, C2), a plurality of transistors (Ml, M2, M3, M4) and a plurality of controllable switches (SW11, ..., SW8, SW111, ..., SW180). The relaxation oscillator uses a switching method such that the roles of current/voltage generator's transistor and current mirror transistor are periodically swapping by the output signal of the relaxation oscillator. Reducing mismatch of operating points between current/voltage generator and current mirror transistors achieves a decrease of frequency degradation caused by aging effect.