RF Switch Bypass Topology With Shunt Isolation for Low NF
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Solution Overview
Problem
RF signal switches face challenges in achieving low input insertion loss (IL) and noise figure (NF) while maintaining high isolation of the bypass path from the low noise amplifier (LNA) input matching network, as existing solutions either degrade the bypass path IL or increase the system NF due to added switches.
Innovation Solution
The RF signal switch circuit design allows connection of RF input terminals to a Switch Output either in-circuit or bypass mode, using a single series switch and isolation shunt switches to isolate the bypass path from the input matching network, with optional integration of a matching network with the target circuit, and employing a 'T' type series/shunt/series bypass switch configuration for enhanced isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a series/shunt switch pair is added before the matching network to isolate the bypass path, then bypass path isolation is improved, but input insertion loss increases and system noise figure degrades
Solution Approach 1:
The patent extracts the isolation function from the signal path by using a shunt switch connected to ground that activates only in bypass mode. This separates the isolation function from the series switch, allowing the series switch to remain closed (minimizing insertion loss) while the shunt switch provides the necessary isolation by shunting unwanted signals to ground without being in the direct signal path.
Solution Approach 2:
The shunt switch acts as an intermediary element that provides isolation without being in series with the signal path. By connecting to ground and activating only when needed, it mediates between the bypass path and the matching network, providing isolation without adding series insertion loss to the LNA input path.
2Reliability
If a series/shunt switch pair is added before the matching network to isolate the bypass path, then bypass path isolation is improved, but device complexity increases
Solution Approach 1:
The shunt switch serves multiple functions: it provides isolation in bypass mode, and when open, it allows the series switch to handle both series switching and implicit isolation functions. This multi-functionality reduces the need for dedicated isolation switches, thereby reducing overall device complexity while maintaining isolation performance.
Solution Approach 2:
The patent merges the isolation function with the shunt switch that is already part of the bypass path architecture. Instead of adding a separate dedicated isolation switch, the shunt switch is designed to perform both its original function and the isolation function, consolidating components and reducing overall system complexity.
3Reliability
If the LNA is bypassed, then the bypass path should be isolated from the LNA input matching network, but the matching network adversely affects the output impedance and degrades bypass path insertion loss
Solution Approach 1:
The shunt switch provides preliminary anti-action by preemptively shunting signals to ground before they can interact with the matching network in bypass mode. This prevents the matching network from adversely affecting the bypass path impedance and insertion loss, countering the harmful effect before it occurs.
Solution Approach 2:
The patent converts the potential harm of the matching network affecting bypass path performance into a benefit by using the shunt switch to ground the matching network input in bypass mode. This transforms the matching network from a source of impedance degradation into an isolated component that does not affect bypass performance, while still serving its purpose in LNA mode.
Data Source
AI summary
An RF signal switch circuit that allows connection of any of N radio frequency (RF) input terminals to a switch output port, either in an in-circuit mode or in a bypass mode. Embodiments of the invention allow for both a single switch in the series input path while still having the ability to isolate the bypass path from an input matching network. In both modes, the circuit simultaneously exhibits low input insertion loss (and thus a low noise factor) and high bypass mode isolation.