TCXO Bias Current Control for Temperature-Stable Oscillation
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Solution Overview
Problem
Temperature-dependent impedance and sensitivity of crystal resonators and variable capacitance elements in temperature-compensated crystal oscillators (TCXOs) lead to fluctuations in oscillation frequency, making it challenging to maintain high accuracy across varying temperatures.
Innovation Solution
Incorporating a bandgap reference circuit and a bias current generating circuit with a current adjusting resistor, which generates a reference voltage and bias current that adjusts for temperature changes, reducing the impact of impedance and sensitivity variations on oscillation frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a variable capacitance element is used for temperature compensation in a TCXO, then the oscillation frequency can be adjusted to compensate for temperature changes, but the temperature-dependent sensitivity of the variable capacitance element causes the oscillation frequency to change when temperature changes
Solution Approach 1:
The invention changes the operating parameters of the variable capacitance element by adjusting the amplitude of the oscillation signal to a predetermined value. This parameter change compensates for the temperature-dependent sensitivity variations, allowing the element to maintain consistent frequency adjustment characteristics across different temperatures despite its inherent sensitivity changes.
Solution Approach 2:
The invention implements a feedback mechanism where the amplitude of the oscillation signal is monitored and controlled to maintain a predetermined value. This feedback loop compensates for temperature-induced sensitivity changes in the variable capacitance element, ensuring that the oscillation frequency remains accurate across the temperature range while preserving the temperature compensation capability.
2Stability of the object's composition
If the gain of the oscillation stage circuit is kept constant to maintain constant amplitude, then the amplitude stability is improved, but the temperature-dependent impedance of the crystal resonator still causes oscillation frequency changes
Solution Approach 1:
The invention intentionally changes the amplitude parameter of the oscillation signal to a predetermined value that compensates for temperature-dependent impedance effects. By adjusting this parameter, the system maintains both amplitude stability and frequency accuracy across temperature variations, overcoming the limitation of constant gain circuits.
3Measurement precision
If high accuracy oscillation frequency is required across temperature changes, then the sensitivity to temperature-dependent impedance and sensitivity variations must be reduced, but conventional TCXO designs cannot achieve this level of accuracy
Solution Approach 1:
The invention changes the amplitude parameter to a predetermined value that specifically compensates for temperature-dependent effects on both the crystal resonator impedance and the variable capacitance element sensitivity. This parameter adjustment reduces the harmful influence of temperature variations, achieving high frequency accuracy across the temperature range that conventional designs cannot attain.
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
This configuration enables highly accurate frequency-temperature characteristics by setting appropriate temperature characteristics for the oscillation signal amplitude, thereby stabilizing the oscillation frequency despite temperature changes.
Implementation Method 1
a bandgap reference circuit that generates a reference voltage having magnitude, which changes depending on the temperature, by using a resistor inserted in a current path through which a current having magnitude, which changes depending on the temperature, flows
Implementation Method 2
a variable capacitance element that is connected to the first or second electrode of the resonator and adjusts an oscillation frequency
Implementation Method 3
an oscillation stage circuit that is connected between a first electrode and a second electrode of a resonator and performs an oscillation operation
Data Source
AI summary
An oscillator includes: an oscillation stage circuit that is connected between a first electrode and a second electrode of a resonator and performs an oscillation operation; a variable capacitance element that is connected to the first or second electrode of the resonator and adjusts an oscillation frequency; a bandgap reference circuit that generates a reference voltage having magnitude, which changes depending on the temperature, by using a resistor inserted in a current path through which a current having magnitude, which changes depending on the temperature flows; and a bias current generating circuit that generates a bias current of the oscillation stage circuit based on the reference voltage, and that, thereby, reduces a change in the oscillation frequency due to the temperature dependence of the impedance of the resonator or the temperature dependence of the sensitivity of the variable capacitance element.