RF Switch Bypass Topology for Low Loss and High Isolation

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Solution Overview

Problem

Existing RF signal switching circuits face challenges in achieving low input insertion loss (IL) and noise figure (NF) while maintaining high isolation, especially when the low noise amplifier (LNA) needs to be bypassed.

Innovation Solution

The RF signal switch circuit design allows for both low loss and high isolation modes by using a configuration where each RF input terminal is connected to three switches: an in-path connector switch, a shunt switch, and a bypass switch. This design isolates the bypass path from the LNA input matching network, reducing insertion loss and noise figure.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If the LNA is bypassed to reduce insertion loss, then the bypass path isolation from the LNA input matching network deteriorates

Engineering Contradiction:

Improveinsertion lossVSAvoidisolation

Core Design Contradiction:

Loss of energyVSObject-affected harmful factors

Solution Approach 1:

The RF switch circuit is divided into multiple independent switching paths: a first switch path for connecting RF input terminals to the LNA input, and a second switch path for bypassing the LNA input. Each path has dedicated switches that can be independently controlled, allowing the bypass path to be isolated from the LNA input matching network while maintaining low insertion loss when bypassing.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces an intermediate switching mechanism with separate control for the bypass path. The bypass switch path acts as an intermediary that can connect RF signals directly to the RF output terminal without passing through the LNA input matching network, thereby providing isolation while maintaining signal integrity and low insertion loss.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If the matching network is isolated from the bypass path, then the noise figure improves, but the device complexity increases

Engineering Contradiction:

Improvenoise figureVSAvoiddevice complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The RF switch circuit is designed with multi-functional switching paths that can serve different purposes. The same basic switch structure is used for both the LNA input path and the bypass path, allowing the circuit to provide both low-noise amplification when needed and low-loss bypass when needed, without requiring entirely separate circuitry for each function.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The circuit employs dynamic switching control where the state of the switches can be changed in real-time based on operational requirements. The bypass switch and LNA input switch can be dynamically configured to provide either the low-noise amplification path or the low-loss bypass path, allowing the system to adapt to different operational modes without physical reconfiguration.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS20250030415A1RF switch with bypass topology

Publication Date: 2025.01.23 PSEMI CORP

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 a low loss mode, in a bypass mode, or, optionally, in a signal function mode. Embodiments of the invention allow for both a single switch in the series input path to a target circuit while still having the ability to isolate the bypass path from the target circuit. In the low loss and bypass mode, the circuit simultaneously exhibits low input insertion loss (and thus a low noise factor) and high bypass mode isolation.