LC VCO Cell Isolation for Common-Mode Noise Suppression
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Solution Overview
Problem
Voltage-controlled oscillators (VCOs) generate undesired common-mode (CM) noise due to non-linear capacitors, causing voltage and frequency offsets in output signals, which affect phase noise and signal integrity.
Innovation Solution
The VCO includes a first and second cell coupled via common-mode isolation circuitry, comprising a transmission line, transformer, and impedance components, to reduce CM noise by inductive uncoupling and adjusting phase relationships between cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If non-linear capacitors are used in the VCO to achieve voltage-to-capacitance conversion, then the oscillation frequency can be controlled, but common-mode noise is generated causing phase and frequency offsets
Solution Approach 1:
The VCO is divided into two separate cells (first cell and second cell), each with its own set of non-linear capacitors and switching circuits. This segmentation allows the common-mode noise generated in each cell to be independent, and when combined differentially, the noise components cancel each other out while the useful signal adds constructively.
Solution Approach 2:
The patent employs asymmetric switching control where the first and second switches in each cell are controlled by complementary control signals. This asymmetric control scheme ensures that the non-linear capacitor effects are exploited for frequency control while the differential configuration suppresses the resulting common-mode noise.
2Reliability
If traditional VCO circuitry is used to generate output signals, then the device can operate, but phase noise and signal integrity are degraded due to CM noise
Solution Approach 1:
The patent introduces an intermediary differential configuration between the two VCO cells. The output of each cell is taken differentially, and the combination of these differential outputs serves as an intermediary mechanism that cancels common-mode noise while preserving the desired oscillation signal, thereby improving phase noise and signal integrity.
3Object-generated harmful factors
If common-mode isolation circuitry is added to reduce CM noise, then phase noise is reduced, but device complexity increases
Solution Approach 1:
The patent merges the common-mode noise suppression function with the existing VCO oscillation generation function by using a differential configuration that serves both purposes simultaneously. The two cells are combined in such a way that the same circuit elements that generate the oscillation signal also provide common-mode rejection, eliminating the need for separate isolation circuitry.
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 minimizing CM noise, enhancing signal-to-noise ratio without increasing power consumption.
Implementation Method 1
a second inductor-capacitor tank circuit coupled to third switch, the fourth switch, and the first inductor-capacitor tank circuit, the second inductor-capacitor tank circuit may inductively couple to the first inductor-capacitor tank circuit
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.