The 2320-2345MHz band is licensed to Sirius XM for broadcasting Satellite Digital Audio Radio Service (SDARS). Out-of-band (OOB) transmissions can disrupt SDARS reception through blocking. The blocker can either emanate from nearby vehicles, or can be selfinflicted because the vehicular SDARS aerial often share a common radome with cellular aerials. Among cellular bands, the Wireless Communications Service’s (WCS) 2305-2320MHz and 2345-2360MHz are the most disruptive because they sandwich SDARS without any guard band. As the SDARS aerial is connected to the receiver through 15-20 feet of coaxial cable, an outboard low noise amplifier (LNA) is necessary to overcome cable loss. Due to stringent noise requirement, the LNAs are predominantly discrete designs which necessitate many components and large printed circuit boards (PCB), but vehicular aesthetic and aerodynamic demand small and unobtrusive radomes. When reception of global navigation satellite system (GNSS) is also required, the additional aerial and LNA further increase the space pressure. A dual-band aerial can eliminate one aerial, but still requires a diplexer to interface with two LNAs. Narrowband receivers conventionally employ a band-select filter before the LNA, i.e. prefilter, as the primary defence against OOB blockers. However, the insertion loss of a miniature microwave filter is incompatible with the SDARS LNA’s noise requirement. The pre-filter will also prevent GNSS reception. In order to reject WCS blockers, the filter must possess narrow fractional bandwidth (~1%) and steep skirts. Most prior arts utilize either surface acoustic wave (SAW) or dielectric filters because they have the required selectivity but they add cost and PCB space. To reduce component count, we integrated RF amplifiers, active biasing, impedance matching and band-filtering into a 5×5mm2 multichip on board (MCOB) module. To save on a separate GNSS LNA, the module is dual-band capable; hence eliminating the need for a diplexer between aerial and LNA. The conflicting requirements for low noise and blocking immunity are satisfied by relocating the filter to mid-LNA and distributing the gain optimally. An SDARS LNA’s blocking tolerance is reported for the first time. In conclusion, this design achieves previously unattainable miniaturization and blocking performance.

Chin-leong Lim
Avago Technologies, Malaysia

SDARS GNSS Low Noise Amplifier, Wireless Communications Service Blocker Tolerant, Cellular Coexistence, Miniaturize
Published By :
Published In :
ICTACT Journal on Microelectronics
( Volume: 4 , Issue: 4 )
Date of Publication :
Januray 2019

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