Differential Varactor Oscillator Circuit for Frequency Drift Suppression
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Solution Overview
Problem
Existing oscillators, such as TCXO, face frequency drift issues due to noise-induced voltage fluctuations, which degrade the accuracy of oscillation frequency.
Innovation Solution
A circuit device with a D/A converter circuit that outputs differential signals to variable capacitance capacitors, where the potential difference between the capacitors changes in opposite directions to reduce frequency fluctuations, and a low-pass filter is used to noise-shape the frequency control data, reducing in-phase noise effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-ended output D/A converter circuit is used to control the variable capacitance capacitor, then the circuit complexity is reduced, but the oscillation frequency accuracy deteriorates due to noise-induced voltage fluctuations
Solution Approach 1:
The patent divides the single control voltage into two separate differential control voltages (Vc1 and Vc2) that independently control two variable capacitance capacitors (Cv1 and Cv2). This segmentation allows the circuit to reject common-mode noise while maintaining control functionality, resolving the contradiction between circuit simplicity and frequency accuracy.
Solution Approach 2:
The patent converts the harmful effect of noise-induced voltage fluctuations into a beneficial differential signal structure. By using differential signaling where both voltages fluctuate in-phase with noise, the common-mode noise is rejected, transforming what would be a harmful single-ended fluctuation into a beneficial noise-rejection mechanism.
2Speed
If the control voltage is directly applied to the variable capacitance capacitor, then the response speed is improved, but the oscillation frequency stability deteriorates due to voltage fluctuations
Solution Approach 1:
The patent implements a feedback mechanism where temperature detection data is used to generate frequency control data, which is then converted to differential control voltages. This closed-loop feedback system continuously compensates for frequency drift while maintaining fast response through the direct voltage application to capacitors.
Solution Approach 2:
The patent changes the control parameter from a single voltage level to a differential voltage pair (Vc1, Vc2). This parameter transformation allows the system to maintain fast response speed while achieving frequency stability through the differential configuration that rejects common-mode fluctuations.
3Stability of the object's composition
If frequency control data is changed in k×LSB units, then the abrupt changes in frequency drift are reduced, but the response time increases
Solution Approach 1:
The patent applies dynamic gradient control where the frequency control data is adjusted in k×LSB units based on temperature changes. This dynamic approach allows the system to maintain stability during normal operation while enabling faster response when larger frequency corrections are needed, balancing stability and response time.
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 effectively reduces oscillation frequency fluctuations and improves the accuracy of the oscillation frequency by canceling out capacitance variations caused by in-phase voltage fluctuations, enhancing the stability of the oscillation circuit.
Implementation Method 1
a D/A converter circuit that performs D/A conversion on frequency control data and outputs a first voltage signal and a second voltage signal which are D/A converted voltage signals of differential signals corresponding to the frequency control data
Implementation Method 2
the variable capacitance circuit includes a first variable capacitance capacitor, to one end of which the first voltage signal is input and, to the other end of which a first bias voltage is input, and a second variable capacitance capacitor
Implementation Method 3
an oscillation circuit that includes a drive circuit driving a resonator
Data Source
AI summary
A circuit device includes a drive circuit driving a resonator, an oscillation circuit having the resonator and a variable capacitance circuit coupled to an oscillation loop including the drive circuit, and a D/A converter circuit that performs D/A conversion on frequency control data and outputs a first voltage signal and a second voltage signal which are differential signals. The variable capacitance circuit includes a first variable capacitance capacitor, to one end of which the first voltage signal is input and, to the other end of which a first bias voltage is input and a second variable capacitance capacitor, to one end of which the second voltage signal is input and, to the other end of which a second bias voltage is input.