STLBC01 datasheet(26/40 Pages) STMICROELECTRONICS

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Application design guidelines

STLBC01

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Application design guidelines

This section provides some design guidelines and constraints are given for proper

application designs. In particular, antenna port and antenna design guidelines, XTAL

oscillator and power supply connections are described. Furthermore, PCB guidelines are

stated in order to achieve an optimum RF-performance.

8.1

Antenna port

The STBLC01 features a fully differential 200 +j0

Ω antenna port for the received or emitted

signals at the pins ANTP and ANTN. The selected input/output impedance allows the

implementation of a folded dipole antenna directly connectable to the antenna port which

does not require any external matching components. Use of other types of antenna is

granted by the implementation of a matching network with few external components. The

following general guidelines can be used to achieve the best results in terms of RF

performance:

Use at least a 2-layer PCB, dedicating the bottom layer to one common ground plane

covering all external components and the chip itself. Connect the attached area pin of

the package to the ground plane.

Keep the STBLC01 ANTN/ANTP symmetry on the PCB by keeping symmetry in

components and via placement as well as line-routing.

Use only 100

Ω transmission lines between the STBLC01 RF output pins and the

antenna / matching network input.

Try to minimize RF trace lengths.

Respect also a 3 mm clearance to ground close to RF transmission lines and/or

matching network components. In particular, respect clearance to ground for antenna

structure (varies with antenna topology).

Do not put a ground plane below the antenna structure to avoid gain loss and directivity

modification.

8.1.1

50 Ohm matching

The STBLC01 antenna impedance can be converted to 50

Ω termination to allow interfacing

with a standard measurement system or with a standard 50

Ω antenna structure. In this

case, a matching circuit which ensures the conversion from the differential 200

Ω antenna

port of the STBLC01 and the single-ended 50

Ω of the instruments, is required. Figure 7

shows an example circuit to implement a matching network. In order to achieve the best RF

performance, the layout around the antenna port - both for the chip and attached antenna

connector - needs to be done while keeping RF guidelines in mind.

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