Cross-Coupled LC VCO Topology for Common-Mode Noise Suppression
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Solution Overview
Problem
Voltage-controlled oscillators (VCOs) in transmitter and/or receiver circuits often experience undesired noise on the phase and frequency of the output signal due to changes in capacitance values of non-linear capacitors, leading to voltage and frequency offsets.
Innovation Solution
The VCO includes a first and second inductor-capacitor tank circuit coupled via common-mode isolation circuitry, which reduces the amplitude of common-mode noise by inductively coupling and uncoupling signals based on their frequency, thereby improving phase noise performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If non-linear capacitors are used in the VCO circuit, then the capacitance value can be adjusted to control oscillation frequency, but changes in capacitance value generate undesired noise on phase and frequency of the output signal
Solution Approach 1:
The VCO circuit is divided into two separate inductor-capacitor tank circuits (first and second tank circuits) that are differentially coupled. Each tank circuit has its own set of non-linear capacitors, and they are coupled through common-mode isolation circuitry. This segmentation allows the noise generated by capacitance changes in one tank to be isolated from the other, thereby reducing the overall phase and frequency noise in the output signal while maintaining the ability to adjust oscillation frequency through capacitance control.
2Device complexity
If a single inductor-capacitor tank circuit is used, then the circuit structure is simple, but common-mode noise has large amplitude and degrades phase noise performance
Solution Approach 1:
Instead of using a single tank circuit, the invention employs two separate inductor-capacitor tank circuits that are differentially coupled. This segmentation transforms the single common-mode noise source into two separate noise sources that can be isolated from each other through the common-mode isolation circuitry, thereby reducing the amplitude of common-mode noise while maintaining a relatively simple overall circuit structure.
Solution Approach 2:
Common-mode isolation circuitry is introduced as an intermediary between the two tank circuits. This isolation circuitry includes coupling elements that allow differential signals to pass while blocking common-mode noise. The intermediary structure enables the two tank circuits to be electrically connected for differential operation while isolating them from common-mode interference, thus reducing common-mode noise amplitude without significantly increasing circuit complexity.
3Object-generated harmful factors
If common-mode isolation circuitry is added to reduce noise, then phase noise performance improves, but device complexity increases
Solution Approach 1:
The VCO is segmented into two symmetrical tank circuits with matched components, which inherently provides noise isolation. The common-mode isolation circuitry is integrated into this segmented structure rather than added as a separate external block, allowing the isolation function to be achieved through the natural differential configuration and coupling between the two tanks, thereby limiting the increase in overall device complexity.
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 reduces the amplitude of undesired common-mode noises, leading to improved phase noise of the output signal, enhancing signal integrity and reducing timing errors in transmission and reception.
Implementation Method 1
reduces the amplitude of common-mode noise by inductively coupling and uncoupling signals based on their frequency
Data Source
AI summary
This disclosure is directed to a Voltage-Controlled Oscillator (VCO) with reduced phase noise compared to other VCOs. The VCO may include a first cell and a second cell separated by common-mode (CM) isolation circuitry. The first cell and the second cell may each include a portion of the CM noise of the VCO. Moreover, gate terminals of switches of the first cell and the second cell may be cross-coupled to drain terminals of the switches of the second cell and the first cell respectively. An interdependency of voltages of the first cell and the second cell may reduce an amplitude of the respective portions of the CM noise on the first cell and the second cell.