Sub-Threshold Crystal Oscillator Biasing for Fast Startup
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Solution Overview
Problem
Pierce crystal oscillators face challenges with high power consumption and insufficient transconductance due to large gate-source voltages, which hinder fast starting oscillation, and are affected by process, voltage, and temperature variations (PVT), leading to uncontrollable power consumption and high-order effects.
Innovation Solution
A crystal oscillator design featuring a stable operating voltage and current, achieved through a second driving circuit that controls the operating transistors to operate in the sub-threshold region, using a ratio of transistor sizes and current control transistors to maintain stable operating conditions, reducing power consumption and enhancing transconductance for faster oscillation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the power supply voltage V DD is increased to provide sufficient transconductance, then the transconductance of MOS transistors is improved, but the gate-source voltages V GS s become excessively large causing serious high-order effects and uncontrollable power consumption
Solution Approach 1:
The patent changes the operating region parameter from above-threshold to sub-threshold region, enabling transistors to achieve sufficient transconductance at lower voltages and avoid high-order effects while maintaining oscillation performance
Solution Approach 2:
The patent introduces dynamic voltage control through a voltage control terminal that adjusts the voltage supplied to oscillating transistors based on oscillation state, optimizing transconductance while preventing excessive gate-source voltages
2Power
If the power supply voltage V DD is increased to ensure sufficient transconductance, then the transconductance is improved, but the power consumption becomes uncontrollable and excessively large
Solution Approach 1:
The patent changes the operating region parameter from above-threshold to sub-threshold region, enabling transistors to achieve sufficient transconductance at lower voltages and avoid high-order effects while maintaining oscillation performance
Solution Approach 2:
The patent introduces dynamic voltage control through a voltage control terminal that adjusts the voltage supplied to oscillating transistors based on oscillation state, optimizing transconductance while preventing excessive gate-source voltages
3Use of energy by moving object
If the gate-source voltages V GS s are reduced to lower power consumption, then the power consumption is improved, but the transconductance becomes insufficient for fast starting oscillation
Solution Approach 1:
The patent changes the operating region parameter from above-threshold to sub-threshold region, enabling transistors to achieve sufficient transconductance at lower voltages and avoid high-order effects while maintaining oscillation performance
Solution Approach 2:
The patent introduces dynamic voltage control through a voltage control terminal that adjusts the voltage supplied to oscillating transistors based on oscillation state, optimizing transconductance while preventing excessive gate-source voltages
4Device complexity
If conventional biasing is used to simplify the circuit, then the device complexity is reduced, but the oscillation amplitude becomes uncontrollable and phase noise performance deteriorates
Solution Approach 1:
The patent implements feedback control where the voltage control terminal receives feedback about the oscillation state and adjusts the voltage to oscillating transistors accordingly, maintaining stable amplitude and improving phase noise performance
Solution Approach 2:
The voltage control terminal serves multiple functions: controlling oscillation amplitude, optimizing transconductance, and suppressing spurious signals, making the circuit more robust without proportionally increasing complexity
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
Provided is a crystal oscillator (10), including: a crystal (200); an oscillating circuit (300) including a first oscillating transistor and a second oscillating transistor, where the first oscillating transistor and the second oscillating transistor are configured to provide transconductance for starting oscillation and maintaining oscillation of the crystal; a first driving circuit (500) configured to generate a stable reference current; and a second driving circuit (400), configured to supply an operating voltage to the oscillating circuit (300) and make an operating current of the first oscillating transistor and the second oscillating transistor be a stable current according to the reference current, where the operating voltage is used to control the first oscillating transistor and the second oscillating transistor to operate in a sub-threshold region.