RF FET Switch Charge-Pump Gating for Faster Isolation Transitions
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Solution Overview
Problem
Radio frequency (RF) switches in communication systems face challenges with slow switching speeds due to the use of gate resistors, which provide isolation but increase turn-on and turn-off times, degrading switching performance.
Innovation Solution
The implementation of a fast switching circuit that includes a field-effect transistor (FET) switch, a digital buffer, and a charge pump to boost supply voltages, allowing for increased switching speed by pulsing the switch control voltage during transitions and using self-opening transistor stacks for protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gate resistors are used to provide isolation, then isolation performance is improved, but switching speed deteriorates
Solution Approach 1:
The fast switching circuit applies a preliminary voltage boost to the gate of the FET switch before the actual switching operation. By pre-charging the gate capacitance through the charge pump circuit, the switch transitions faster while the gate resistor maintains its isolation function during steady state.
Solution Approach 2:
The charge pump circuit operates periodically during switching transitions to boost the gate voltage. This periodic activation provides fast switching only when needed (during state transitions) while leaving the gate resistor in place during steady-state operation to maintain isolation performance.
2Speed
If fast switching circuit with charge pumps is added, then switching speed is improved, but device complexity increases
Solution Approach 1:
The fast switching circuit is integrated with the existing FET switch and gate resistor structure. The charge pump circuit shares the gate node with the FET, and the gate resistor remains connected to maintain isolation. This merging approach adds fast switching capability without requiring completely separate circuitry.
Solution Approach 2:
The gate resistor serves as an intermediary element that reconciles the conflict between fast switching and isolation. It remains in the circuit to provide isolation during steady state, while the charge pump temporarily overcomes its limiting effect during switching transitions by boosting the gate voltage.
3Speed
If boosted supply voltages are applied to FET switch, then switching speed is improved, but component protection becomes challenging
Solution Approach 1:
Self-opening transistor stacks are placed in series with the charge pump output before the boosted voltage reaches the FET gate. These transistors act as protective buffers that automatically open (turn off) when voltage exceeds safe levels, preventing damage to the FET and other components while still allowing fast switching 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
This solution enhances switching speed without impacting other performance characteristics like linearity, power handling, or insertion loss, improving transient performance without adding circuitry that could degrade the RF switch.
Implementation Method 1
The fast switching circuit can include one or more charge pumps configured to boost the power high and power low supply voltages which are also used by the buffer
Data Source
AI summary
Radio frequency switches with improved switching speed are provided. In certain embodiments, an RF switching circuit includes a FET switch including a gate, a digital buffer configured to provide a first output voltage to the gate of the FET during a steady-state, and a fast switching circuit in parallel with the digital buffer and configured to provide a second output voltage to the gate of the FET during a switching state. The fast switching circuit includes at least one charge pump configured to boost at least one supply voltage to a multiple of the at least one supply voltage. The fast switching circuit is configured to generate the second output voltage based on the boosted at least one supply voltage.