RF Switch Bypass Network for Faster Switching Without RF Loss
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Solution Overview
Problem
Existing RF switches face a tradeoff between switching speed and RF performance due to the high RC time constant associated with MOS transistors, which limits the reduction of switching time despite increasing demands for faster switching in cellular networks.
Innovation Solution
The RF switch employs a bypass network with additional transistors that short the gate bias resistor and current path during switching transients, reducing the RC constant to improve switching speed, and then restore it to a high value during normal operation to maintain RF performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the RC time constant is reduced to improve switching speed, then switching time decreases, but RF performance deteriorates due to loss of high impedance necessary for minimal DC bias influence
Solution Approach 1:
The patent applies dynamics by making the RC time constant adjustable rather than fixed. A bypass transistor is introduced that can dynamically switch between two states: during switching transients, the bypass transistor activates to short the gate bias resistor, reducing the RC time constant and enabling fast switching; during normal operation, the bypass transistor is off, maintaining the high impedance state for optimal RF performance. This dynamic adaptation resolves the contradiction by allowing the system to have both fast switching and good RF performance at different times.
2Speed
If a bypass network is added to accelerate switching, then switching speed improves, but device complexity increases due to additional transistors and control circuits
Solution Approach 1:
The bypass transistor serves multiple functions: it acts as a switch to reduce the RC time constant during switching transients, and it is controlled by the existing control signal infrastructure. The control network reuses the main control signal to activate the bypass transistor, eliminating the need for completely separate control circuits. This multi-functionality approach accelerates switching while minimizing the increase in device complexity.
Data Source
AI summary
A radio frequency (RF) switch includes a switchable RF path including a plurality of transistors coupled in series; a gate bias network including a plurality of resistors, wherein the gate bias network is coupled to each of the plurality of transistors in the switchable RF path; and a bypass network including a first plurality of transistors coupled in parallel to each of the plurality of transistors in the switchable RF path and a second plurality of transistors coupled in parallel to each of the plurality of resistors in the gate bias network.