Schmitt Trigger Ring Oscillator With Fast Clock Edges at Nanowatt Power
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Solution Overview
Problem
In IoT and ultra-low power sensor applications, existing oscillators consume excessive quiescent current, limiting the battery life of portable devices and requiring improved designs for low-frequency clock signals with minimal power consumption.
Innovation Solution
An ultra-low power oscillator topology using Schmitt trigger delay cells in a ring configuration with threshold settings equal to supply voltages, coupled with a non-overlap buffer to generate a clock signal with fast transitions and minimize short circuit currents, achieving low energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional oscillators are used to generate low-frequency clock signals, then the oscillator can provide continuous timing functionality, but the quiescent current consumption is excessive
Solution Approach 1:
The oscillator uses periodic action by implementing a wake-up timer that operates in periodic intervals rather than continuously. The circuit can be put into sleep mode and periodically awakened to generate clock signals only when needed, thereby dramatically reducing quiescent current consumption while maintaining reliable timing functionality for battery-powered IoT devices.
Solution Approach 2:
The oscillator employs dynamic power management by allowing the circuit to transition between active and sleep states. The wake-up timer dynamically controls when the oscillator is enabled, adjusting its operation based on system requirements rather than running continuously, thus reducing power consumption while ensuring timing functionality is available when needed.
2Use of energy by moving object
If the oscillator operates at low frequency to reduce power consumption, then energy usage decreases, but the transition speed of clock signals becomes slower
Solution Approach 1:
The oscillator circuit is segmented into multiple functional blocks including separate delay elements, Schmitt trigger stages, and output buffers. This segmentation allows different parts of the circuit to be optimized independently - the delay elements can operate at low frequency to minimize power consumption, while the output buffer stage can be designed to provide fast transition speeds when clock signals are actually generated.
Solution Approach 2:
Different parts of the oscillator circuit have different local qualities optimized for their specific functions. The delay elements use high-impedance nodes and Schmitt triggers with hysteresis to achieve long delay times at low power, while the output buffer uses strong drive capability to provide fast rising and falling edges. This local optimization resolves the contradiction between low power operation and fast transitions.
3Productivity
If Schmitt trigger delay cells are used with thresholds equal to supply voltages, then delay time increases reducing the number of cells needed, but the circuit complexity increases
Solution Approach 1:
The Schmitt trigger delay cells use parameter changes by setting the switching thresholds equal to the supply voltages (VDD and VSS). This parameter configuration maximizes the delay time achieved by each delay cell, as the full supply voltage swing is utilized. The standardized parameter choice simplifies design and reduces the number of cells needed, offsetting the increased complexity of individual cells.
Solution Approach 2:
The Schmitt trigger delay cells serve multiple functions: they provide delay, signal regeneration, and threshold detection. By making each cell multi-functional, the overall circuit complexity is reduced despite the sophisticated behavior of individual cells. The universal Schmitt trigger design can be replicated multiple times with consistent parameters, simplifying analysis and implementation.
Data Source
AI summary
In described examples of an integrated circuit (IC), an oscillator includes Schmitt trigger delay cells connected in a ring topology. The Schmitt trigger delay cells have a high input threshold approximately equal to Vdd and a low input threshold approximately equal to Vss to increase delay through each cell. An output buffer receives a phase signal from an output terminal of one of the Schmitt trigger delay cells and converts a transition phase signal to a faster transition clock signal. The output buffer has control circuitry that generates non-overlapping control signals in response to the phase signal, to control an output stage to generate the fast transition clock signal while preventing short circuit current in the output stage.