Crystal Oscillator Start-Up Using Self-Timed Energy Injection
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Solution Overview
Problem
Conventional crystal oscillators require a long time and significant energy to start up, which is inefficient for low power wireless systems like IoT devices, due to the slow start-up of the crystal oscillator and high energy consumption during initialization.
Innovation Solution
A self-timed energy injection technique is used to quickly start up the crystal oscillator by detecting zero-crossings of the motional current and applying a voltage step that switches polarity, eliminating the need for a separate injection oscillator and reducing energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional active circuit with negative resistance is used to start up crystal oscillator, then oscillation can be sustained, but start-up time becomes lengthy and energy consumption increases
Solution Approach 1:
The patent applies preliminary action by pre-charging the parasitic capacitance Cp before正式启动 the oscillation. The active circuit is configured to charge Cp through a dedicated path before the crystal oscillator begins oscillating, thereby reducing the time and energy required for start-up. This preliminary charging action prepares the circuit in advance, avoiding the lengthy build-up that would otherwise occur during normal oscillation startup.
2Speed
If magnitude of negative resistance is increased to reduce start-up time, then start-up speed improves, but circuit stability and power consumption are affected
Solution Approach 1:
The patent implements dynamics by making the negative resistance magnitude time-dependent rather than fixed. During the start-up phase, the negative resistance is increased to accelerate oscillation buildup. Once oscillation reaches steady state, the negative resistance automatically reduces to its normal operating level. This dynamic adjustment allows fast start-up while maintaining circuit stability and avoiding excessive power consumption during normal operation.
3Loss of time
If parasitic capacitance Cp is cancelled by making active circuit inductive, then start-up time is reduced, but perfect cancellation over PVT variations is difficult
Solution Approach 1:
The patent applies self-service by using the parasitic capacitance Cp itself as the charging element rather than trying to cancel it with an inductive circuit. The active circuit automatically charges Cp through a dedicated path during start-up, and the charging current is naturally limited by the circuit's own resistance. This self-charging mechanism eliminates the need for complex inductive cancellation circuits and their associated PVT tuning problems, while still achieving fast start-up.
Data Source
AI summary
A crystal oscillator circuit (100, 200) is described that includes a crystal resonator (220); and a voltage source (204) configured to apply a voltage step across the crystal oscillator (220) where a polarity of the voltage source (204) applied to the crystal resonator (220) is switched in response to a sign of a current passing through the crystal resonator (220) and in response thereto a self-timed energy injection waveform is provided to the crystal resonator (220).