RF Switch Branch Biasing for Fast Turn-On and High Q
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Solution Overview
Problem
Radio Frequency (RF) switches face a design trade-off between achieving fast response times and high power handling while maintaining a high Quality Factor (Q) in the off state, as large bias resistor values are required for high Q but lead to long switching times due to large Resistor-Capacitor (RC) time constants.
Innovation Solution
The implementation of auxiliary shorting switches using local bias networks, which short the gate and drain/source bias resistor ladders during turn-on, and a rectification circuit that generates a local body bias to reduce body current flow, allowing for accelerated turn-on and improved power handling without additional bias resistor networks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large bias resistor values are used to achieve high Q factor in the off state, then the Quality Factor is improved, but the switching time increases due to large RC time constants
Solution Approach 1:
The patent applies preliminary action by using auxiliary shorting switches to preemptively discharge the gate and drain/source capacitances before the main switching event. This preliminary discharge action reduces the RC time constant effect, allowing fast switching without requiring smaller bias resistors, thus maintaining high Q factor while achieving fast switching times.
Solution Approach 2:
The patent introduces auxiliary shorting switches as intermediary elements that mediate between the bias resistor network and the main switching devices. These auxiliary switches provide a temporary low-impedance path for discharge current, allowing the use of large bias resistors for high Q while enabling fast switching through the intermediary discharge path.
2Loss of time
If low bias resistor values are used to reduce RC time constants and improve switching speed, then the switching time is reduced, but the power handling capability decreases due to DC voltage drop
Solution Approach 1:
The auxiliary shorting switches perform preliminary discharge of capacitances before switching, enabling the use of low bias resistor values for fast switching without suffering from excessive DC voltage drop during normal operation. The low resistor values only affect the circuit during the brief discharge transient, not during steady-state power handling.
Solution Approach 2:
The patent makes the bias network dynamic by introducing auxiliary switches that temporarily alter the resistance values during switching transitions. During normal operation, high resistance values maintain power handling, while during switching events, low resistance values achieve fast switching speeds.
3Speed
If low bias resistor values are used to improve switching responsiveness, then the turn-on speed is improved, but the power handling capability decreases
Solution Approach 1:
The auxiliary shorting switches perform preliminary discharge of gate and drain/source capacitances before the main switching devices turn on. This preliminary action enables fast turn-on speed without requiring low bias resistor values, thus maintaining power handling capability while achieving improved turn-on speed.
Solution Approach 2:
The patent segments the switching function into two parts: auxiliary shorting switches handle the fast discharge/turn-on function, while the main bias resistor network maintains power handling. This segmentation allows each component to be optimized for its specific function without compromise.
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 approach significantly reduces switching times while maintaining a high Q factor and improving power handling, especially during high-VDS conditions, by bypassing gate and source-drain resistors with auxiliary switches and using a rectification circuit to manage body current.
Implementation Method 1
a rectification circuit for rectifying a voltage across the source and drain terminal to provide a local body bias
Data Source
AI summary
Improved Radio Frequency (RF) switches are provided herein. According to one aspect, an RF switch comprises one or more stages. In one embodiment, each stage comprises a signal input terminal, a signal output terminal, a control input terminal, and a switching device having a source connected to the signal input terminal, a drain connected to the signal output terminal, a gate for controlling the on/off state of the switching device, and a body terminal. Each stage includes a gate resistor connected in series between the control input terminal and the gate and a rectification circuit for rectifying a voltage across the source and drain to provide a local bias voltage to the body terminal.