Multi-Band LC Tank VCO with Dynamic Conductance for Low Phase Noise
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Solution Overview
Problem
Multi-band wireless devices face challenges in achieving reduced phase noise over a large tuning range due to variations in resistive impedance of LC tank circuits, leading to increased cost and area in integrated circuit implementations when using multiple VCOs for different frequency bands.
Innovation Solution
An LC tank VCO with adjustable active conductance is implemented, using a digital-to-analog converter to adjust the negative conductance based on the current frequency setting, optimizing phase noise performance across various frequency bands without requiring additional cross-coupled pairs or switches, which helps in minimizing phase noise while ensuring oscillation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single LC tank VCO is used to cover multiple frequency bands, then the device complexity is reduced, but the phase noise performance deteriorates due to large variations in resistive impedance over the tuning range
Solution Approach 1:
The patent implements dynamic adjustment of the active conductance value based on the current frequency band of operation. The controller selects different conductance values from a set of available values to match each frequency band, allowing the VCO to maintain optimal phase noise performance across multiple bands while using a single physical VCO circuit. This dynamic reconfiguration resolves the contradiction by making the conductance parameter adaptive rather than fixed.
Solution Approach 2:
The patent changes the electrical parameter (active conductance) of the VCO circuit depending on the operating frequency band. By having a set of different conductance values that can be selected and applied to the LC tank circuit, the system optimizes the resistive impedance matching for each frequency band, thereby maintaining low phase noise across the entire tuning range while using only one VCO structure.
2Reliability
If multiple VCOs are used for different frequency bands, then the phase noise performance is improved for each band, but the device complexity and area increase
Solution Approach 1:
The patent makes a single VCO circuit universal by enabling it to serve multiple frequency bands through dynamic conductance adjustment. The same physical VCO structure can be optimized for different bands by changing the active conductance value, eliminating the need for separate dedicated VCOs for each frequency band. This multi-functionality approach resolves the contradiction by achieving band-specific optimization without multiplying the hardware count.
Solution Approach 2:
Instead of using multiple VCOs with fixed parameters, the patent uses one VCO with variable conductance parameters. The controller selects appropriate conductance values from a predefined set to match each frequency band's requirements, allowing a single circuit to achieve the performance that would otherwise require multiple circuits with different fixed parameters.
3Reliability
If the active conductance is increased to reduce phase noise, then the phase noise performance improves, but the oscillation stability may deteriorate due to excessive negative conductance
Solution Approach 1:
The patent uses a set of discrete conductance values that are carefully selected to provide optimal phase noise performance for each frequency band without exceeding the stability threshold. The controller chooses from these pre-determined values based on the operating band, ensuring that the conductance is high enough to reduce phase noise but not so high as to cause oscillation instability. This controlled parameter selection resolves the contradiction.
Solution Approach 2:
The system incorporates a controller that monitors the operating frequency band and selects the appropriate conductance value accordingly. This feedback mechanism ensures that the active conductance is optimized for each band while maintaining oscillation stability, preventing the conductance from being set too high which would cause instability. The controller acts as a feedback element that balances phase noise reduction with stability maintenance.
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 reduces phase noise across multiple frequency bands by dynamically adjusting the active conductance, thereby improving the performance of multi-band wireless devices without increasing cost or area, supporting a wide tuning range with enhanced RF front-end efficiency.
Implementation Method 1
using a digital-to-analog converter to adjust the negative conductance based on the current frequency setting
Implementation Method 2
The VCO is typically implemented using an inductor-capacitor (LC) tank circuit that includes an inductor and one or more capacitors. The frequency of the LO signal generated by the VCO can be controlled by varying the capacitance of the LC tank.
Implementation Method 3
an active module to provide a negative, active conductance that is used to compensate for a positive conductance associated with the tank module
Data Source
AI summary
Embodiments of a multi-band voltage controlled oscillator (VCO) are provided herein. The multi-band VCO is configured to adjust a frequency of an output signal based on an input signal. The multi-band VCO includes a tank module, an active module, and a control module. The tank module includes a parallel combination of a capacitor and an inductor. The active module includes a pair of cross-coupled transistors that are configured to provide a negative conductance that cancels out a positive conductance associated with the tank module. To improve the phase noise associated with the multi-band VCO, the control module is configured to adjust the body voltage of the cross-coupled transistors.