Quartz Oscillator Bias Circuit for Wide Voltage and Temperature Range
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Solution Overview
Problem
Existing amplitude-controlled oscillators for electronic devices face challenges in achieving high transconductance without degrading the power supply rejection rate, and they often require higher supply voltages and larger surface area, which increases cost and reduces performance.
Innovation Solution
The oscillator circuit employs two complementary active transistors with integrated polarizing means and a voltage and temperature stable current source, along with an inverting amplifier and capacitive divider, to achieve high transconductance while maintaining a low power supply rejection rate and reducing surface area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two complementary active transistors are used in series to achieve high transconductance, then the transconductance level is improved, but the power supply rejection rate is degraded and the supply voltage requirement increases
Solution Approach 1:
An independent voltage stable current source is introduced as an intermediary element to provide stable polarisation current to the two complementary transistors. This current source acts as a mediator that decouples the transistors from direct power supply variations, thereby maintaining high transconductance while preserving power supply rejection rate. The current source converts the power supply voltage into a stable current that is less sensitive to voltage fluctuations.
Solution Approach 2:
The invention changes the operating parameters by using a current-mode approach instead of voltage-mode. By converting the power supply voltage into a stable current through the independent current source, and by carefully selecting the polarisation voltages (with a specific voltage shift between the two transistors), the system achieves high transconductance while maintaining immunity to power supply variations. This parameter transformation from voltage to current domain resolves the contradiction.
2Stability of the object's composition
If high capacitance is used in parallel with the active transistors to stabilize operation, then the oscillation stability is improved, but the surface area occupied increases and the cost increases
Solution Approach 1:
The invention changes the stabilisation approach from using large capacitance values to using optimized smaller capacitance values combined with an independent voltage stable current source. The current source provides stable operating conditions that reduce the dependency on large capacitance for filtering and stabilisation. This parameter optimization allows achieving the same stability with smaller capacitance values, thereby reducing the surface area occupied by capacitive elements.
3Reliability
If the polarisation voltage is increased to ensure active operating conditions for both transistors, then the transconductance is improved, but the supply voltage requirement increases
Solution Approach 1:
The invention optimizes the polarisation voltage parameters by introducing a specific voltage shift relationship between the two complementary transistors. Instead of uniformly increasing both voltages, the system uses differential polarisation where each transistor operates at its optimal voltage point. The independent voltage stable current source ensures that adequate current flows through both transistors to maintain active operating conditions without requiring excessive supply voltage. This parameter optimization achieves high transconductance with minimal supply voltage requirement.
Data Source
AI summary
The invention concerns an oscillator including an input terminal, an output terminal, a resonator, and an oscillator circuit including: first and second power supply terminals, two capacitors connected between the first power supply terminal and the input terminal, and respectively the output terminal of the oscillator; first and second active transistors of complementary type, forming therewith an inverting amplifier, first and second means for respectively polarizing the first and the second active transistors, a first current source formed by a transistor of the same type as the second active transistor, between the second power supply terminal and the second active transistor, current control means for the second polarizing means, characterized in that in an steady operating conditions, said second polarizing means are arranged for providing a polarization voltage across the gate of the second active transistor corresponding to the transistor gate voltage of the first current source to within one voltage shift.