RF Switch Circuit With 50 Ohm Termination for Antenna Isolation
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Solution Overview
Problem
In wireless communication systems supporting multi-mode multi-band, the integration of multiple front end modules (FEMs) sharing an antenna leads to worsened isolation characteristics between antennas, resulting in radiated spurious emissions (RSE) due to signals being transmitted to adjacent antennas.
Innovation Solution
The RF switch circuit includes a configuration of four switches connected to an antenna port, with a switch control circuit managing their states to minimize current consumption and reduce RSE. In low power mode, switches S1 to S5 are turned off, and switch S6 is turned on to maintain 50 Ohm termination at the antenna port.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple FEMs share one antenna to support multi-mode multi-band, then integration increases, but isolation characteristics between antennas worsen resulting in radiated spurious emissions
Solution Approach 1:
The antenna system is segmented into multiple antenna ports, each with dedicated RF switches and termination circuits. This allows independent control of each antenna port's connection state, enabling selective termination of specific ports to prevent spurious emissions while maintaining multi-mode multi-band operation capability
Solution Approach 2:
RF switch circuits are introduced as intermediary components between the FEMs and antenna ports. These switches act as mediators that can isolate or connect antenna ports as needed, preventing direct signal leakage between antennas while preserving the ability to support multiple modes and bands
2Device complexity
If RF switches are placed close to antenna to be located at the end of FEM, then integration increases, but isolation characteristics between antennas worsen
Solution Approach 1:
The RF switch system is segmented into multiple independently controllable units, each associated with a specific antenna port. This segmentation allows precise control over which ports are active or terminated, maintaining isolation between antennas even when switches are integrated close to the antenna elements
3Use of energy by moving object
If switches S1 to S5 are turned off and switch S6 is turned on in low power mode, then current consumption decreases, but antenna port termination must be maintained
Solution Approach 1:
The termination circuit is designed to be automatically activated when the RF switches are turned off in low power mode. The circuit self-regulates to maintain proper 50 Ohm termination at the antenna port without requiring additional active power consumption, as the termination resistors are always present but only become electrically relevant when switches are off
Data Source
AI summary
A radio frequency (RF) switch circuit and a method for operation of a RF switch circuit. The RF switch circuit may include a first switch connected between a first port and an antenna port, a second switch connected between a second port and the antenna port, a third switch connected between the antenna port and ground, a fourth switch connected between the antenna port and the ground, and a switch control circuit configured to control the first switch, the second switch, and the third switch to be turned off and the fourth switch to be turned on in a low power mode.