Stacked FET RF Switch With End-Network Voltage Equalization
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Solution Overview
Problem
Transistor-based RF switches face stringent linearity requirements due to downlink and uplink carrier aggregation, necessitating improved linearity performance to minimize noise from circuit nonlinearities, particularly in complex wireless communications devices.
Innovation Solution
A transistor-based RF switch design featuring N main FETs stacked in series with gate and body resistors, along with end-networks providing variable impedance to equalize drain-to-source voltages, reducing harmonic generation and enhancing linearity by balancing gate and body bias voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple FETs are stacked in series to achieve symmetric RF impedance, then linearity performance is improved, but device complexity increases
Solution Approach 1:
The RF switch is divided into multiple FETs (N≥3) stacked in series, with each FET contributing to the overall symmetric impedance. This segmentation allows the voltage to be distributed across multiple devices, improving linearity while maintaining manageable complexity through modular design
Solution Approach 2:
The patent addresses impedance asymmetry by using end-networks with specific impedances connected to the first and last FETs. The end-networks are designed to compensate for the inherent asymmetry in the FET stack, creating overall symmetric RF impedance at the switch terminals, which reduces even-order harmonics and improves linearity
2Reliability
If end-networks with variable impedance are added to equalize drain-to-source voltage, then linearity is improved, but device complexity increases
Solution Approach 1:
End-networks are introduced as intermediary components connected between the RF signal path and the gate control nodes. These end-networks with variable impedance (Zend1 and Zend2) act as mediators to equalize the drain-to-source voltage across the FET stack, improving voltage balance and linearity without requiring modification of the core FET structures
Solution Approach 2:
The end-networks utilize variable impedance that can be adjusted based on operating conditions. By changing the impedance parameters of the end-networks, the patent optimizes voltage equalization across different RF signal levels and frequencies, thereby improving linearity performance under varying operational scenarios
Data Source
AI summary
A transistor-based radio frequency (RF) switch that provides symmetric RF impedance is disclosed. The transistor-based RF switch includes an N number of main field-effect transistors (FETs) stacked in series between a first end node and a second end node. A first end-network is coupled between the first end node and a proximal gate node. The first end-network provides a first variable impedance that equalizes a drain-to-source voltage of the first main FET to within a predetermined percentage of a drain-to-source voltage of a second main FET of the N number of main FETs. A second end-network is coupled between the second end node and the distal gate node, wherein the second end-network provides a second variable impedance to equalize the drain-to-source voltage of an Nth main FET to within the predetermined percentage of the drain-to-source voltage of an N−1 main FET of the N number of main FETs.