RF Switch Dynamic Bias Circuit for Isolation and Harmonic Control
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Solution Overview
Problem
Mobile RF transceivers using SOI technology face challenges with device isolation, RF loss, and floating body effect, leading to parasitic transistors, OFF-state leakage, and out-of-band harmonics, which degrade performance.
Innovation Solution
A dynamic bias control circuit is implemented in RFICs, incorporating a switch FET with a body resistor, gate resistor, and a capacitor, coupled with transistors to dynamically bias the body and gate, reducing parasitic effects and improving breakdown voltage and harmonic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SOI technology is used to reduce parasitic device capacitance, then device isolation is improved, but out-of-band harmonics increase due to the floating body effect
Solution Approach 1:
A body contact transistor is introduced as an intermediary element between the body contact and ground. This transistor provides a controlled path for charge泄放, mediating the interaction between the floating body and ground to prevent harmful charge accumulation that generates out-of-band harmonics, while preserving the isolation benefits of SOI technology
Solution Approach 2:
The body contact voltage is dynamically adjusted by controlling the gate voltage of the body contact transistor. By changing the operating parameters (voltage levels) of the body contact, the transistor can operate in different regions (cutoff, linear, saturation) to optimally manage charge泄放 and minimize harmonic generation while maintaining device isolation
2Object-generated harmful factors
If a thicker BOX layer is used to reduce artificial harmonics, then harmonic performance is improved, but device isolation decreases
Solution Approach 1:
The body contact transistor serves as an active intermediary that compensates for reduced BOX layer thickness. By providing a controlled charge泄放 path, it mitigates the harmful effects of charge accumulation that would otherwise be suppressed by a thicker BOX, enabling thin BOX designs to achieve both low harmonics and good isolation
Solution Approach 2:
The invention changes the electrical parameters at the body contact interface by introducing a controllable transistor. This allows dynamic adjustment of the body potential to maintain optimal performance despite the reduced physical separation provided by a thinner BOX layer
3Object-generated harmful factors
If the body contact is directly connected to ground, then charge accumulation is reduced, but OFF-state leakage increases due to parasitic transistors
Solution Approach 1:
The body contact transistor acts as a smart intermediary between the body contact and ground. Unlike a direct connection, it provides conditional charge泄放 only when needed, preventing parasitic transistor activation while still managing charge accumulation. The transistor's controlled operation allows it to泄放 charge during ON-state and remain non-conductive during OFF-state, eliminating leakage
Solution Approach 2:
The body contact connection is made dynamic through the use of a controllable transistor rather than a static direct connection. The transistor's operation mode can be dynamically switched between cutoff and conduction states based on the switch FET's operation phase, enabling adaptive charge management that reduces both charge accumulation and OFF-state leakage
Data Source
AI summary
A radio frequency integrated circuit (RFIC) is described. The RFIC includes a switch field effect transistor (FET) including a source region, a drain region, a body region coupled to a body resistor, and a gate region coupled to a gate resistor. The RFIC also includes a dynamic bias control circuit. The dynamic bias control circuit includes at least one transistor coupled to the body region of the switch FET through the body resistor and coupled to the gate region of the switch FET through the gate resistor. The at least one transistor is an RF silicon on insulator (SOI) device. The dynamic bias control circuit also includes a capacitor coupled to the gate resistor and the body resistor and coupled in parallel with each transistor in the dynamic bias control circuit.