RF Switch Gate-Resistor Shorting for Faster DPDT Switching
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Solution Overview
Problem
RF switch applications face significant delays due to high gate capacitance and resistance, leading to long switching times, particularly in large double pole double throw (DPDT) switches, which can be exacerbated by voltage swings that exceed the breakdown voltage of transmission gate switches.
Innovation Solution
A switching circuit is implemented with a transmission gate comprising a PMOS and NMOS, coupled with level shifters to apply complementary dynamic pulses, shorting the gate resistor only during transitions to reduce RC time constants and switching time, while avoiding breakdown voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a large RF switch is used to achieve double pole double throw (DPDT) switching capability, then the switching function is improved, but the gate capacitance and gate resistance increase causing longer switching time
Solution Approach 1:
The gate resistor is divided into multiple segments (first gate resistor and second gate resistor) that can be independently controlled. This segmentation allows each resistor segment to be shorted separately during switching transitions, reducing the overall RC time constant while maintaining the necessary voltage swings for large DPDT switch operation
Solution Approach 2:
Transmission gates are activated before the main RF switch transitions to preemptively short the gate resistors. This preliminary action reduces the RC time constant in advance, enabling faster switching transitions without exceeding the breakdown voltage of the transmission gates
2Speed
If the gate resistor is shorted during switching transitions, then the RC time constant is reduced improving switching speed, but the voltage swing may exceed the breakdown voltage of the transmission gate
Solution Approach 1:
The transmission gates are dynamically controlled with pulse signals that activate them only during the brief transition periods when switching speed is critical. This dynamic control allows the gate resistors to be shorted temporarily to improve switching speed while remaining open during steady-state operation to prevent voltage swing-induced breakdown
Solution Approach 2:
Pulse signals are applied periodically to the transmission gates to short the gate resistors only during the specific time windows when switching transitions occur. This periodic action provides the speed benefit during transitions while avoiding the breakdown issue during steady-state operation
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 significantly reduces switching time and turn-on time of RF switches by dynamically shorting the gate resistor, maintaining performance and reducing degradation, even in large RF switches with wide voltage swings.
Implementation Method 1
A gate capacitance and/or resistance of an RF Switch can create large resistor-capacitor (RC) time constant delays and/or can result in a relatively long switching time
Data Source
AI summary
A switching circuit comprises a radio frequency (RF) switch, a gate resistor, a voltage source, a transmission gate, and coupling circuitry configured to couple a gate of the RF switch, a first side of the gate resistor, and the transmission gate at a first node and the voltage source, a second side of the gate resistor, and the transmission gate at a second node.