Tunable Common-Mode Rejection Circuit for Variable-Frequency Oscillators
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Solution Overview
Problem
Existing common mode rejection circuits in high-frequency oscillators suffer from reduced quality factor and increased power consumption due to unaddressed common mode currents, which negatively impact signal purity and phase noise performance.
Innovation Solution
An adjustable common mode rejection circuit element with a resonant circuit that can be tuned to match the oscillation frequency, utilizing switchable capacitors or inductors to maximize impedance at common mode frequencies, thereby enhancing common mode rejection without reducing the quality factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a common mode rejection circuit is added to reject common mode currents, then signal purity and phase noise performance are improved, but device complexity and power consumption increase
Solution Approach 1:
The common mode rejection circuit is integrated within the existing oscillator structure by nesting the resonant circuit into the feedback path of the differential amplifier. This allows the common mode rejection functionality to be embedded within the oscillator core, achieving signal purity improvement without proportionally increasing overall device complexity
Solution Approach 2:
A resonant circuit is introduced as an intermediary element between the differential amplifier and the output stage. This resonant circuit acts as a frequency-selective mediator that selectively rejects common mode currents at the oscillation frequency while maintaining the differential signal path, thereby improving signal purity without requiring complex filtering networks
2Object-affected harmful factors
If a common mode rejection circuit is added to reject common mode currents, then phase noise performance is improved, but power consumption increases
Solution Approach 1:
The resonant circuit is designed to operate at mechanical resonance frequencies corresponding to the oscillation frequency, utilizing the natural resonant properties of LC tanks to achieve high Q-factor common mode rejection. This resonance-based approach provides effective phase noise suppression while consuming minimal power compared to active filtering solutions
Solution Approach 2:
The circuit parameters (inductance and capacitance values) of the resonant circuit are optimized to achieve maximum common mode rejection at the specific oscillation frequency. By tuning the resonant frequency to match the oscillation frequency, the circuit achieves optimal phase noise performance with minimal power dissipation in the rejection network
3Device complexity
If a fixed common mode rejection circuit is used, then circuit simplicity is maintained, but adaptability to variable frequency ranges is reduced
Solution Approach 1:
The resonant circuit incorporates variable inductance or capacitance elements that allow the resonant frequency to be dynamically adjusted across different frequency ranges. This dynamic tuning capability enables the common mode rejection circuit to adapt to variable oscillation frequencies while maintaining a relatively simple circuit topology based on the fundamental LC resonant structure
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
The solution effectively rejects common mode currents across a variable frequency range, improving signal purity, reducing power consumption, and enhancing phase noise performance by maintaining a high quality factor and minimizing energy dissipation.
Implementation Method 1
a resonant circuit configured to reject a common mode current through the oscillator, wherein a resonance frequency of the resonant circuit is adjustable
Data Source
AI summary
An electrical circuit includes a circuit element and a common mode rejection circuit element. The circuit element is configured to operate at a selected frequency within a variable frequency range and the common mode rejection circuit element is configured to reject a common mode current through the circuit element, wherein the common mode rejection circuit element is adjustable.