Switched Termination Circuit for RF Front End IMD Suppression
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Solution Overview
Problem
Conventional front end systems in RF communication face a tradeoff between intermodulation distortion (IMD) performance and isolation, with impedance mismatch issues arising from shunting inactive transmit paths to ground, leading to degraded linearity and performance.
Innovation Solution
Incorporating switched termination circuits in shunt with RF signal paths to suppress impedance variation when paths are inactive, maintaining impedance matching and enhancing IMD performance across frequency ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If inactive transmit paths are shunted to ground, then isolation is improved, but impedance matching deteriorates causing degraded linearity and IMD performance
Solution Approach 1:
A termination circuit is introduced as an intermediary component between the inactive transmit path and ground. This termination circuit includes a switch and a termination resistor that together provide a controlled impedance path to ground when the transmit path is inactive, rather than directly shunting to ground. The intermediary termination resistor maintains proper impedance matching while still providing the isolation needed.
Solution Approach 2:
The impedance parameter of the inactive transmit path is dynamically changed based on its operational state. When active, the path operates with its normal characteristic impedance. When inactive, the switch closes to connect the termination resistor, changing the impedance parameter to match the termination resistor value, thereby maintaining impedance matching across different states.
2Reliability
If termination circuits are added to maintain impedance matching, then IMD performance is improved, but device complexity increases
Solution Approach 1:
The termination circuit is designed to serve multiple functions: it provides impedance matching when transmit paths are inactive, maintains isolation between active and inactive paths, and preserves the natural impedance when active. This multi-functionality reduces the need for separate components for each function, thereby limiting the increase in overall device complexity.
Solution Approach 2:
The termination circuit automatically activates and deactivates based on the operational state of the transmit paths through control signals. The circuit self-regulates its impedance presentation without requiring external intervention or complex control logic, simplifying the overall system control architecture.
Data Source
AI summary
Front end systems with switched termination for enhanced intermodulation distortion performance are provided herein. The switched termination can be used on transmit paths and/or receive paths of the front end system to suppress impedance variation when the signal paths are inactive. For example, with respect to switched termination for transmit paths, a front end system can include a frequency multiplexing circuit connected to a band switch by a first radio frequency (RF) signal path and by a second RF signal path. The band switch selectively provides the frequency multiplexing circuit with a first transmit signal over the first RF signal path and with a second transmit signal over the second RF signal path. The front end system further includes a switched termination circuit in shunt with the first RF signal path and operable to turn on to suppress impedance variation when the first RF signal path is inactive.