Relaxation Oscillator Circuit With Transistor Role Swapping
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Relaxation oscillators experience frequency degradation due to aging effects, particularly channel hot carrier injection (CHC) and operating point mismatch between transistors, which existing auto-zeroing techniques cannot fully address.
Innovation Solution
The implementation of a relaxation oscillator with a switching method that periodically swaps the roles of transistors in the current/voltage generator and current mirror, using controllable switches to charge and discharge capacitors, thereby reducing the mismatch in operating points and minimizing the channel hot carrier effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If auto-zeroing is used to cancel comparator offset degradation, then comparator offset degradation is reduced, but operating point mismatch between transistors remains unaddressed
Solution Approach 1:
The patent segments the transistor roles into distinct functional groups (charging transistors and reference transistors) that are periodically swapped. This segmentation allows independent optimization and aging compensation for each group, addressing the operating point mismatch that auto-zeroing alone cannot resolve.
Solution Approach 2:
The patent implements periodic swapping of transistor roles between charging and reference functions. This periodic action allows the system to average out aging effects and operating point drifts over time, providing long-term frequency stability that complements the immediate offset correction from auto-zeroing.
2Device complexity
If transistors operate continuously in fixed roles, then circuit operation is simple, but channel hot carrier injection causes threshold voltage shifts and frequency degradation
Solution Approach 1:
The patent applies periodic swapping of transistor roles to distribute the channel hot carrier injection stress across multiple transistors over time. By rotating which transistors serve as charging vs. reference devices, the aging effects are averaged out, maintaining frequency accuracy without requiring complex real-time adjustment mechanisms.
Solution Approach 2:
The patent changes the operational parameters (role assignments) of transistors periodically rather than maintaining fixed roles. This parameter change allows the system to adapt to aging effects and maintain performance, balancing the simplicity of fixed roles with the need for long-term reliability.
3Reliability
If transistor roles are swapped frequently, then channel hot carrier effect is reduced, but switching losses and power consumption increase
Solution Approach 1:
The patent implements transistor role swapping at a periodic rate optimized to balance aging compensation benefits against switching losses. The swap frequency is chosen to be low enough to minimize energy loss from frequent switching while high enough to effectively average out channel hot carrier injection effects over the oscillator's operating lifetime.
Data Source
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 (M1, 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 minor transistors achieves a decrease of frequency degradation caused by aging effect.