LNA articles

Compact & blocker-tolerant low-noise amplifier for satellite radio

posted 17 May 2020, 13:51

Satellite Digital Audio Radio Service's (SDARS) reception over 2320-2345MHz can be blocked by cellular transmissions in the neighbouring bands. In vehicles, the blocking is exacerbated by SDARS sharing a common radome with cellular aerials. Considering the SDARS satellites are ~40,000km away, this is an extreme example of the near-far problem.

Among cellular services, the Wireless Communications Service's (WCS) 2305-2320MHz and 2345-2360MHz bands are the most disruptive because they sandwich SDARS without any guard band.

As SDARS aerial on the car roof is connected to the receiver through a long coaxial cable, an outboard low noise amplifier (LNA) is necessary to overcome cable loss. A compact LNA is required because of the small radome.

Conventionally, a band-select filter before the LNA (pre-filter), is used to defend against blockers, but the filter's insertion loss can significantly degrade the overall noise figure. Furthermore, the space constraint necessitates a miniature filter which accentuates the loss. To reject WCS, the filter must possess narrow fractional bandwidth (~1%) and steep skirts.

To reduce component count, we integrated amplifiers, biasing, impedance matching and filters into a 5×5mm 2 multi-chip on board (MCOB) module. The conflicting requirements for low noise and blocking immunity are satisfied by relocating the filter to mid-LNA. In conclusion, this design achieves previously unattainable miniaturization and blocking performance.

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SDARS-GNSS LNA that can coexist with cellular

posted 17 May 2020, 13:41 by biastee biastee   [ updated 17 May 2020, 13:52 ]

Satellite Digital Audio Radio Service (SDARS) reception (2320-2345 MHz) can be disrupted by cellular transmissions. Among cellular bands, the Wireless Communications Service’s (WCS) 2305-2320 MHz and 2345-2360 MHz are the most disruptive because they sandwich SDARS without any guard band.

As the SDARS aerial is connected to the receiver through a long coaxial cable, an outboard low noise amplifier (LNA) is necessary to overcome loss. Due to stringent noise requirement, the LNAs are predominantly discrete designs which necessitate many components and large printed circuit boards (PCB). When reception of global navigation satellite system (GNSS) is also required, the additional aerial and LNA further increase the space pressure.

Narrowband receivers conventionally employ a pre-filter before the LNA as the primary defence against blockers but the miniature filter's insertion loss is incompatible with the SDARS noise requirement. The pre-filter will also prevent GNSS reception. The filter must possess narrow fractional bandwidth (~1%), such as surface acoustic wave (SAW) or dielectric filters, but they are costly and bulky.

To reduce component count, we integrated amplifiers, biasing, impedance matching and filtering into a miniature multi-chip on board (MCOB) module. To save on a separate GNSS LNA, the module is dual-band capable; hence eliminating the need for a diplexer. 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.

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