Distributed Back-Bias Network for High-Voltage RF MOSFET Stacks
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Solution Overview
Problem
MOSFET-based RF switches in RF communication systems face challenges with voltage handling capability, linearity, and distortion due to parasitic capacitances and resistances, leading to crosstalk and interference, which are exacerbated by the need for high-voltage handling and space constraints in modern cellular systems.
Innovation Solution
A distributed back-bias network structure is implemented using series-coupled integrated circuit (IC) SOI MOSFETs with substrate contacts coupled to a bias voltage through a resistive ladder, setting a fixed DC bias for the IC substrate while decoupling MOSFETs from RF voltages, thereby enhancing voltage handling and reducing parasitic effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If MOSFETs are series-connected in stacks to withstand high-voltage RF signals, then voltage handling capability is improved, but parasitic capacitances and resistances increase causing distortion and crosstalk
Solution Approach 1:
The substrate is divided into multiple independently biasable regions, with each region serving a specific MOSFET or group of MOSFETs in the stack. This segmentation allows individual back-bias control for each segment, enabling optimization of voltage handling while minimizing parasitic effects through localized biasing strategies.
Solution Approach 2:
Different back-bias voltages are applied to different substrate regions based on local requirements. Regions with higher voltage stress receive appropriate biasing to enhance breakdown voltage, while other regions are biased to minimize parasitic capacitances. This local quality approach allows simultaneous optimization of voltage handling and distortion reduction in different parts of the circuit.
2Power
If antenna switches handle higher voltages to meet power requirements, then power handling capability is improved, but linearity deteriorates due to increased parasitic effects
Solution Approach 1:
The back-bias voltage parameter is dynamically adjusted based on operating conditions. By changing the substrate bias voltage, the electrical characteristics of the MOSFETs are modified to maintain optimal linearity across different power levels. This parameter change allows the circuit to adapt to varying power requirements while preserving signal linearity.
3Volume of moving object
If space constraints lead to compact antenna placement, then device miniaturization is achieved, but crosstalk and interference coupling increase
Solution Approach 1:
Parasitic substrate effects are extracted and controlled through dedicated substrate contacts and biasing circuits. By explicitly managing the substrate interaction through extracted parasitic paths, the design can compensate for close antenna spacing effects and reduce crosstalk despite compact placement.
4Productivity
If MOSFETs are used as ideal switches with zero resistance in ON state, then switching efficiency is improved, but actual MOSFETs exhibit non-zero resistance causing insertion loss
Solution Approach 1:
The substrate back-bias voltage is optimized to achieve the best trade-off between ON-state resistance and breakdown voltage. By carefully selecting the bias voltage parameter, the MOSFET operates at optimal points that minimize insertion loss while maintaining adequate voltage handling capability, thus improving overall switching efficiency.
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 increases the voltage handling capability and harmonic knee point of MOSFETs, mitigating loss, leakage, crosstalk, and distortion, while maintaining linearity and power handling, making the RF switches more suitable for antenna applications.
Implementation Method 1
substrate contacts coupled to a bias voltage through a resistive ladder
Data Source
AI summary
Electronic circuits and methods encompassing an RF switch comprising a plurality of series-coupled (stacked) integrated circuit (IC) SOI MOSFETs having a distributed back-bias network structure comprising groups of substrate contacts coupled to a bias voltage source through a resistive ladder. The distributed back-bias network structure sets the common IC substrate voltage at a fixed DC bias but resistively decouples groups of MOSFETs with respect to RF voltages so that the voltage division characteristics of the MOSFET stack are maintained. The distributed back-bias network structure increases the voltage handling capability of each MOSFET and improves the maximum RF voltage at which a particular MOSFET is effective as a switch device, while mitigating loss, leakage, crosstalk, and distortion. RF switches in accordance with the present invention are particularly useful as antenna switches.