Crystal Oscillator Buffer Isolation for Fast Start-Up
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Solution Overview
Problem
Crystal oscillators in mobile devices take longer to achieve stable oscillations due to higher Effective Series Resistance (ESR) in cheaper crystals, leading to increased start-up time when powered on.
Innovation Solution
Incorporating a gain stage with negative resistance and a buffer to isolate the shunt capacitance, increasing the negative resistance and reducing the start-up time by boosting the rate of oscillation signal growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If cheaper crystals with higher ESR are used, then cost is reduced, but start-up time increases
Solution Approach 1:
A buffer stage is introduced as an intermediary component between the gain stage and the crystal. This buffer isolates the gain stage from the crystal's shunt capacitance, preventing the capacitance from reducing the negative resistance. The buffer acts as a mediator that protects the gain stage while allowing the crystal to operate with its higher ESR, thus enabling the use of cheaper crystals without increasing start-up time.
Solution Approach 2:
The invention changes the electrical parameters of the oscillator circuit by increasing the negative resistance of the gain stage. By operating the gain stage at a higher negative resistance (achieved through optimal biasing and the buffering effect), the circuit compensates for the higher ESR of cheaper crystals. This parameter change allows the system to maintain fast start-up performance while using lower-cost crystal components.
2Speed
If negative resistance is increased, then rate of oscillation signal growth increases, but circuit complexity increases
Solution Approach 1:
The buffer stage serves as an intermediary that enables the gain stage to operate at higher negative resistance without being adversely affected by the crystal's shunt capacitance. This intermediary component allows the circuit to achieve faster oscillation signal growth while maintaining a relatively simple overall structure, as the buffer is a standard, easily implemented circuit element.
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 significantly reduces the start-up time of crystal oscillators by increasing the negative resistance, allowing for faster stabilization of oscillations, even with cheaper crystals commonly used in mobile devices.
Implementation Method 1
a gain stage with negative resistance... An increase in the negative resistance increases the rate of growth of an oscillation signal in the oscillator
Implementation Method 2
crystal oscillators, which employ vibrating crystals to create electrical signals with very precise frequencies
Implementation Method 3
a buffer is coupled to the gain stage of the crystal oscillator such that the buffer can isolate the gain stage from the crystal shunt capacitance
Data Source
AI summary
An exemplary fast start-up crystal oscillator with reduced start-up time. The exemplary oscillator reduces the start-up time (i.e., the time taken to attain sustained stable oscillations after the power is turned on) by increasing the negative resistance of a circuit. Increasing the negative resistance increases the rate of growth of the oscillations, thereby reducing start-up time. The exemplary crystal oscillator includes a gain stage with negative resistance. A crystal with shunt capacitance is placed in the feedback loop of the gain stage. A buffer is coupled to the gain stage such that it blocks the crystal shunt capacitance from loading the gain stage, effectively increasing the negative resistance of the gain stage. Further, an oscillation detection and control circuit is coupled between the crystal and the gain stage. The oscillation detection and control circuit connects the buffer during start-up, and disconnects the buffer once an oscillation signal attains sustained stable oscillations.