Dual Mode Antenna Switch Module Phase Shifting Network
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Solution Overview
Problem
Commercially available RF switches are not sufficiently linear, leading to significant 3rd order intermodulation products that can affect the sensitivity of UMTS receivers in 3G handsets when handling blocker signals, especially when operating in multiple frequency bands.
Innovation Solution
A dual mode antenna switch module (ASM) is configured with a phase shifting network between the SP7T RF switch and the UMTS duplexer to adjust the phase of the reflection coefficient, minimizing intermodulation products by ensuring a low impedance at the RF switch in the frequency range of 1730 MHz to 1790 MHz, thereby reducing the generation of IM products.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a commercially available RF switch is used to interface multiple bands, then the device can operate on multiple GSM and UMTS bands, but significant 3rd order intermodulation products are generated that degrade UMTS receiver sensitivity
Solution Approach 1:
A phase shifting network is introduced as an intermediary component between the RF switch and the UMTS duplexer. This network modifies the phase of signals in the blocker frequency range (1730-1790 MHz) to create destructive interference of intermodulation products, thereby reducing their impact on receiver sensitivity while maintaining multi-band operation capability
Solution Approach 2:
The phase shifting network dynamically adjusts the phase parameter of signals in specific frequency ranges. By changing the phase of reflection coefficient in the 1730-1790 MHz range, the system minimizes intermodulation product generation at the UMTS RX port, allowing the RF switch to maintain its multi-band functionality without degrading receiver performance
2Device complexity
If switching circuits are used to separate TX and RX signals for GSM bands, then simultaneous TX and RX is not required, but this approach is not suitable for UMTS where simultaneous TX and RX is required
Solution Approach 1:
The frequency spectrum is segmented into different bands with distinct handling approaches. GSM bands use time-division switching while UMTS bands utilize frequency-division separation through the duplexer. The phase shifting network is selectively applied only to the UMTS path, creating a hybrid architecture that optimizes for both switching efficiency and simultaneous TX/RX capability
Solution Approach 2:
The RF switch is designed to handle multiple functions: GSM band switching and UMTS band selection. By integrating it with a UMTS-specific phase shifting network and duplexer, the system achieves universal compatibility with both GSM time-division operation and UMTS frequency-division simultaneous TX/RX operation
3Adaptability or versatility
If a duplexer is used to separate UMTS TX and RX in the frequency domain, then simultaneous TX and RX is enabled, but intermodulation products from blocker signals still affect receiver sensitivity
Solution Approach 1:
The phase shifting network serves as a mediator between the RF switch and duplexer, specifically targeting intermodulation products generated in the 1730-1790 MHz range. It applies phase modulation to these products to create destructive interference, reducing their amplitude at the UMTS RX port while preserving the duplexer's frequency-domain separation function
Solution Approach 2:
The phase shifting network converts the harmful intermodulation products into beneficial destructive interference patterns. By carefully controlling the phase shift, the intermodulation products that would normally degrade receiver sensitivity are transformed into signals that cancel each other out, effectively turning a harmful phenomenon into a protective mechanism
Data Source
AI summary
A dual mode antenna switch module (ASM) comprises a UMTS TX port; a UMTS RX port; and a UMTS duplexer, comprising a common port, a TX port coupled to the UMTS TX port and an RX port coupled to the UMTS RX port. The ASM further comprises an antenna port; at least one GSM TX port; and at least one GSM RX port. A multi-port switch has respective ports coupled to the antenna port, the at least one GSM TX port, the at least one GSM RX port, and the common port of said UMTS duplexer. The common port of said duplexer has a reflection co-efficient at said connected multi-port switch port with a magnitude in the range 0.8 to 1.0 and with a phase, φ, where −210°≦φn×360≦−150° where N is an integer.