LC VCO Tank Circuit Topology for Common-Mode Noise Separation
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Solution Overview
Problem
Voltage-controlled oscillators (VCOs) generate undesired common-mode noise due to changes in capacitance values of non-linear capacitors, leading to phase and frequency noise in output signals, which affect signal quality and power consumption.
Innovation Solution
The VCO incorporates a first and second inductor-capacitor tank circuit coupled via common-mode isolation circuitry, including transformers and impedance circuits, to separate and reduce common-mode noise, improving signal-to-noise ratio without increasing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If non-linear capacitors are used in the VCO circuit, then the oscillation frequency can be tuned, but common-mode noise is generated causing phase and frequency instability
Solution Approach 1:
The VCO circuit is divided into two separate tank circuits (first and second LC tank circuits) with each having its own set of non-linear capacitors. This segmentation isolates the noise-generating elements into separate units, allowing the common-mode noise from each tank to be differentiated and rejected, thereby maintaining frequency tuning capability while improving phase and frequency stability.
Solution Approach 2:
The patent converts the harmful common-mode noise generated by non-linear capacitors into a useful feature by exploiting the correlation between noise sources in identical circuit configurations. By using matched tank circuits with identical non-linear capacitor implementations, the common-mode noise appears as a correlated signal that can be rejected through differential processing, turning the noise-generating property of non-linear capacitors into a mechanism for noise cancellation.
2Reliability
If traditional noise reduction filters are added to reduce phase noise, then signal quality improves, but power consumption increases
Solution Approach 1:
The VCO circuit performs noise reduction autonomously through its inherent differential architecture and common-mode rejection properties. The matched tank circuits automatically generate correlated noise signals that cancel each other out without requiring external active filtering components or additional power-consuming noise reduction circuitry, achieving signal quality improvement while maintaining low power consumption.
3Device complexity
If a single LC tank circuit is used, then the circuit is simple, but common-mode noise from non-linear capacitors directly affects the output signal
Solution Approach 1:
The single LC tank circuit is segmented into two separate but identical tank circuits, each containing its own non-linear capacitors. This segmentation transforms the single source of common-mode noise into two correlated noise sources that can be differentiated and rejected, reducing the harmful effects while maintaining a relatively simple overall circuit structure.
Solution Approach 2:
The patent employs homogeneous circuit designs for both tank circuits, using identical component configurations and non-linear capacitor implementations. This homogeneity ensures that both tanks generate identical common-mode noise characteristics, which is essential for the common-mode rejection mechanism to effectively cancel the noise while maintaining signal integrity.
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 reduces phase noise and improves signal integrity by uncoupling common-mode noise, allowing for higher voltage amplitude signals with reduced power consumption, enhancing the performance of transmitter and receiver circuits.
Implementation Method 1
a second inductor-capacitor tank circuit that may inductively couple to the first inductor-capacitor tank circuit to generate an output signal having a desired oscillation frequency within a resonant frequency range based on the DC signal, the second inductor-capacitor tank circuit may inductively uncouple from the first inductor-capacitor tank circuit based on signals having an undesired oscillation frequency outside the resonant frequency range
Data Source
AI summary
This disclosure is directed to a Voltage-Controlled Oscillator (VCO) with improved phase noise compared to other VCOs. The VCO may include a first cell and a second cell separated by common-mode (CM) isolation circuitry to reduce an amplitude of CM noise at an output signal. The CM isolation circuitry may inductively couple the first cell to the second cell for generating the output signal based on a resonant frequency range including resonant frequencies of the CM isolation circuitry, the first cell, and the second cell. As such, the first cell and the second cell may each include a portion of an entirety of the CM noise. In some cases, the portions of the CM noise on the first cell and/or the second cell may improve a signal to noise ratio of the output signal.