Crystal Oscillator Startup Circuit With Transconductance Switching
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Solution Overview
Problem
Existing crystal oscillator designs face challenges in reducing startup time while minimizing size, complexity, and potential damage to the external crystal oscillator, often requiring large onboard switchable capacitors and rail-to-rail voltage impulses that can be detrimental.
Innovation Solution
An oscillator apparatus with a transconductance circuit and switch architecture that uses a negative transconductance circuit and controlled switches to rapidly start and maintain resonant oscillations in a crystal oscillator, employing differential voltage excitation below rail-to-rail levels to stimulate oscillations efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If large onboard switchable capacitors and rail-to-rail voltage impulses are used to reduce startup time, then startup time is reduced, but the crystal oscillator may be damaged and complexity increases
Solution Approach 1:
The patent changes the voltage parameter by using differential voltage excitation below rail-to-rail levels instead of full rail-to-rail impulses. This parameter modification allows the oscillator to start quickly while preventing damage to the crystal oscillator from excessive voltage stress.
Solution Approach 2:
The patent introduces a transconductance circuit as an intermediary between the voltage source and the crystal oscillator. This circuit converts voltage signals to current signals, enabling controlled excitation that reduces startup time without directly applying harmful rail-to-rail voltage impulses to the crystal oscillator.
2Loss of time
If large onboard switchable capacitors are used to reduce startup time, then startup time is reduced, but device size and complexity increase
Solution Approach 1:
The patent extracts and eliminates the need for large onboard switchable capacitors by using a transconductance circuit with controlled switches. This removes the bulky capacitor components while maintaining fast startup performance through alternative circuitry that is less complex and more integrated.
Solution Approach 2:
The patent replaces the mechanical switching of large capacitors with an electronic transconductance circuit that uses controlled switches to generate current excitation. This substitution eliminates the need for physically large components and reduces overall device complexity while achieving the same startup time improvement.
3Loss of time
If rail-to-rail voltage impulses are used to reduce startup time, then startup time is reduced, but reliability decreases due to potential damage
Solution Approach 1:
The patent modifies the voltage parameter by using differential voltage excitation that stays below rail-to-rail levels. This parameter change maintains the fast startup performance while improving reliability by preventing voltage-induced damage to the crystal oscillator, thus achieving both speed and reliability goals.
4Object-affected harmful factors
If conventional oscillator startup methods are used, then crystal oscillator is protected from damage, but startup time increases
Solution Approach 1:
The patent introduces a transconductance circuit as an intermediary that enables fast startup without directly applying harmful voltage impulses to the crystal oscillator. This intermediary circuit converts voltage to current, providing controlled excitation that achieves rapid startup while maintaining protection from damage.
Solution Approach 2:
The patent changes the excitation method from high-voltage rail-to-rail impulses to lower-voltage differential excitation through a transconductance circuit. This parameter change allows the crystal oscillator to start quickly while remaining protected from voltage-induced damage, resolving the trade-off between speed and protection.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables a fast startup time of approximately 30 μs with reduced risk of damage to the crystal oscillator, avoiding the need for large capacitors and rail-to-rail voltage impulses, thus improving reliability and reducing complexity and cost.
Implementation Method 1
a transconductance circuit... a negative transconductance circuit
Implementation Method 2
uses the resonant response from a piezoelectric element, sometimes referred to as a crystal, to produce the AC clock signal
Implementation Method 3
uses the resonant response from a piezoelectric element
Data Source
AI summary
An oscillator apparatus, including a first node adapted to be coupled to a first terminal of a crystal oscillator; a second node adapted to be coupled to a second terminal of the crystal oscillator; a transconductance circuit; a first switch coupled between the first node and the second node; and a second switch coupled between the transconductance circuit and the second node.