RF Switch Body Bias Network for Hot Switching Linearity
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Solution Overview
Problem
Traditional RF switches with off-state linearization networks require external bias circuitry and are inefficient under hot switching conditions, leading to harmonic distortion and real estate issues.
Innovation Solution
A radio frequency switch with a body bias network and diode stacks that decouples the gate terminal from the body terminal during transitions, eliminating the need for external bias circuitry and enhancing off-state linearity and reliability under hot switching conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a traditional off-state linearization network is placed in parallel with the RF switch to reduce harmonic distortion, then the harmonic distortion is reduced, but the circuit real estate increases due to external bias circuitry requirements
Solution Approach 1:
The body bias network merges the linearization function with the existing body terminal of the FET switch, eliminating the need for separate external bias circuitry. The network uses the body terminal as an integral part of the linearization mechanism, combining what were previously separate functions into a unified structure that reduces circuit real estate while maintaining harmonic distortion reduction.
Solution Approach 2:
The body bias network utilizes the body terminal of the FET switch itself to generate the necessary bias conditions for linearization. By using the switch's own body terminal as the reference point for the linearization network, the circuit serves itself rather than requiring external bias circuitry, thereby reducing the overall circuit footprint while maintaining the harmonic distortion reduction benefit.
2Reliability
If transmit signals are applied to the RF switch in the off-state, then the RF switch blocks the signals, but undesirable harmonics are generated from the transmit signals due to non-linear capacitance
Solution Approach 1:
The body bias network acts as an intermediary between the gate terminal and body terminal, introducing intermediate control nodes that modify the voltage distribution across the FET. This intermediary structure linearizes the capacitance variation by controlling the body-gate voltage relationship, thereby reducing harmonic generation while maintaining the signal blocking function.
Solution Approach 2:
The body bias network dynamically changes the body-gate voltage parameter in response to the gate voltage, thereby linearizing the overall capacitance characteristic of the FET. By adjusting the body terminal voltage as a function of the gate voltage, the network compensates for the non-linear capacitance effects that would otherwise generate harmonics during signal blocking.
3Adaptability or versatility
If the RF switch transitions from off-state to on-state under hot switching conditions, then the switch needs to handle transmit-level RF signals during transition, but traditional switches without body bias networks struggle with reliable transitions
Solution Approach 1:
The body bias network performs preliminary action by pre-conditioning the body-gate voltage relationship before the actual switching transition occurs. During hot switching conditions, the network anticipates the transition by gradually adjusting the body terminal voltage in response to gate voltage changes, preparing the FET for the upcoming state change and ensuring reliable transition under transmit-level RF signal conditions.
Solution Approach 2:
The body bias network introduces dynamic control of the body-gate voltage relationship, allowing the switch to adapt in real-time during transitions. The network dynamically adjusts the body terminal voltage based on the instantaneous gate voltage, enabling the switch to handle hot switching conditions reliably by continuously optimizing the voltage distribution during the transition from off-state to on-state.
Data Source
AI summary
A radio frequency switch made up of a plurality of switch cells coupled in series between a first node and a second node is disclosed. Each of the plurality of switch cells has a switch field-effect transistor (FET) having a switch drain terminal, a switch source terminal, a switch gate terminal, and a switch body terminal. A body bias network having a first body bias FET with a first drain terminal coupled to the switch body terminal includes a first cross-FET with a second drain terminal coupled to a first source terminal of the first bias body FET and a second source terminal coupled to the switch gate terminal. A second body bias FET has a third drain terminal coupled to the switch body terminal, and a second cross-FET has a fourth drain terminal coupled to a third source terminal of the second body bias FET.