Transformer LC-VCO Layout for Low Phase Noise Tuning
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Solution Overview
Problem
Inductance-capacitance voltage-controlled oscillators (LC-VCOs) face challenges in achieving low phase noise while maintaining low power consumption, primarily due to single-ended parasitic capacitance.
Innovation Solution
The design incorporates a transformer-based LC-VCO with a majority of the total capacitance coupled to the secondary stage, using a capacitor bank and varactors to reduce single-ended capacitance, and a gain stage with cross-coupled transistors to prevent single-ended capacitance from affecting the output, thereby minimizing phase noise and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If single-ended capacitance is used in LC-VCO design, then circuit simplicity is maintained, but phase noise increases significantly
Solution Approach 1:
The patent divides the capacitance into two distinct components: a first capacitance connected to the differential output nodes and a second capacitance connected to the common mode node. This segmentation allows the second capacitance to provide necessary DC blocking and frequency tuning functionality while the first capacitance maintains low single-ended capacitance at the differential outputs, thereby reducing phase noise while preserving circuit functionality.
Solution Approach 2:
The patent introduces a common mode node as an intermediary between the differential output and the capacitance elements. This common mode node serves as a mediator that allows capacitance to be coupled to the output through a balanced configuration, preventing direct single-ended capacitance connection to the differential outputs and thus reducing phase noise while maintaining tuning capability.
2Adaptability or versatility
If capacitance is increased for frequency tuning, then frequency range is improved, but single-ended capacitance increases causing higher phase noise
Solution Approach 1:
The capacitance is segmented into a first capacitance for frequency tuning connected to differential nodes and a second capacitance for DC blocking connected to the common mode node. This allows the tuning capacitance to be increased for broader frequency range while the second capacitance configuration prevents this increased capacitance from manifesting as single-ended capacitance at the outputs, thus avoiding phase noise degradation.
Solution Approach 2:
The patent applies different capacitance configurations to different parts of the circuit: the first capacitance is optimized for frequency tuning at the differential nodes, while the second capacitance is specifically positioned at the common mode node to provide DC blocking with minimal impact on differential output. This local differentiation allows aggressive frequency tuning without proportionally increasing harmful single-ended capacitance effects.
3Use of energy by moving object
If power consumption is reduced, then energy efficiency is improved, but phase noise performance deteriorates
Solution Approach 1:
The balanced configuration with the common mode node and second capacitance provides self-service functionality by automatically blocking single-ended capacitance effects without requiring additional active components or control circuits. This passive self-service approach reduces power consumption compared to active phase noise cancellation techniques while still achieving low phase noise through the inherent symmetry of the balanced architecture.
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 results in a VCO with significantly reduced phase noise and low power consumption, as demonstrated by a 58 GHz VCO achieving -110 dBc/Hz phase noise at 1 MHz offset, outperforming other designs.
Implementation Method 1
a transformer-based LC-VCO with a majority of the total capacitance coupled to the secondary stage
Implementation Method 2
using a capacitor bank and varactors to reduce single-ended capacitance
Implementation Method 3
a gain stage with cross-coupled transistors to prevent single-ended capacitance from affecting the output
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
Embodiments provide a voltage controlled oscillator (VCO) having reduced single-ended capacitance. In one embodiment, the VCO may include a transformer, a capacitor bank, and a gain stage. The transformer may include a primary inductor and a secondary inductor, and the secondary inductor may be inductively coupled to the primary inductor. The capacitor bank may be coupled to the secondary inductor and may provide a majority of a total capacitance of the VCO. The gain stage may be coupled to the primary inductor and configured to receive a supply signal and to drive a differential current in the primary inductor, thereby inducing an output signal across the secondary inductor having a frequency equal to a resonant frequency of the VCO.