Oscillator Circuit With Variable Capacitance for High PSRR
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Solution Overview
Problem
Existing oscillator circuits and phase locked loops face challenges in achieving a high power supply rejection ratio, which is essential for maintaining phase noise and stability in electronic circuits.
Innovation Solution
The proposed solution involves an oscillator circuit with a current source, an oscillating section, a variable capacitor, and a setting section that adjusts impedance based on the voltage at the connection node, using a MOS capacitor and a variable capacitance section to vary capacitance and impedance, thereby enhancing the power supply rejection ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed capacitance decoupling capacitor is used in the oscillator circuit, then the circuit structure is simple, but the power supply rejection ratio is low
Solution Approach 1:
The patent applies the dynamics principle by replacing the fixed capacitance decoupling capacitor with a variable capacitance section that can dynamically adjust its capacitance value. The variable capacitance section includes multiple capacitors connected in parallel with switching elements, allowing the total capacitance to be varied based on operating conditions. This dynamic adjustment optimizes the power supply rejection ratio across different frequency ranges while maintaining circuit functionality.
Solution Approach 2:
The patent implements parameter changes by varying the capacitance value of the decoupling capacitor based on the oscillation frequency and operating conditions. The control circuit monitors the operation frequency and adjusts the capacitance parameter accordingly, selecting appropriate capacitor combinations to maximize power supply rejection ratio at different frequency points. This parameter optimization resolves the contradiction between simple structure and high performance.
2Reliability
If the capacitance of the decoupling capacitor is increased to improve power supply rejection ratio, then the power supply rejection ratio increases, but the oscillation frequency stability deteriorates
Solution Approach 1:
The patent uses dynamics by implementing a control circuit that dynamically adjusts the capacitance value based on real-time monitoring of the oscillation frequency. When the frequency drifts, the control circuit modifies the capacitance to compensate and restore stability. This dynamic feedback mechanism allows the system to maintain frequency stability while utilizing higher capacitance values for improved power supply rejection ratio.
Solution Approach 2:
The patent applies feedback principles through a control circuit that continuously monitors the oscillation frequency and adjusts the capacitance of the decoupling capacitor accordingly. The feedback loop detects frequency deviations and commands the variable capacitance section to adjust its value, creating a self-correcting system that maintains frequency stability despite using higher capacitance values that would otherwise degrade stability.
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 increases the power supply rejection ratio by varying impedance and capacitance in response to voltage changes, reducing phase noise and improving stability in the oscillator circuit and phase locked loop.
Implementation Method 1
The first capacitor has a capacitance that varies in accordance with a voltage at the connection node
Data Source
AI summary
An oscillator circuit includes a current source, an oscillating section, a first capacitor, and a setting section. The current source is coupled to a connection node and causes a current having a current value based on an input voltage to flow from a first power node to the connection node. The oscillating section is on a current path between the connection node and a second power node. The oscillating section oscillates at an oscillation frequency based on a current flowing through the current path. The first capacitor is between the connection node and the second power node. The first capacitor has a capacitance that varies in accordance with a voltage at the connection node. The setting section that performs variation operation based on the voltage at the connection node. The variation operation is operation of varying an impedance between the connection node and the second power node.