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SI4785

Si47XX ANTENNA, SCHEMATIC, LAYOUT, AND DESIGN GUIDELINES

Silicon Laboratories 

AN383

7.3. FM/WB Whip Antenna Bill of Materials

Table 16. FM/WB Whip Antenna Bill of Materials

Designator

WIP_ANTENNA

L1

C5

U3

Description

Whip Antenna

Tuning Inductor, 0603, SM, 56 nH,

MURATA, LQW18AN56nJ00D

AC coupling capacitor,

1 nF, 10%, COG

IC, SM, ESD DIODE, SOT23-3, Cali-

fornia Micro Devices, CM1213-01ST

7.4. FM/WB Whip Antenna Layout

Place the chip as close as possible to the whip antenna. This will minimize the trace length between the device and

whip antenna which in turn will minimize parasitic capacitance and the possibility of noise coupling. Place inductor

L1 and the antenna connector together and as far from potential noise sources as possible and away from the I/O

signals of the Si4736/37/38/39. Place the ac coupling capacitor, C5, as close to the FMI pin as possible. Place ESD

diode U3 as close as possible to the whip antenna input connector for maximum effectiveness.

7.5. FM/WB Whip Antenna Design Checklist

 Maximize whip antenna length for optimal performance.

 Select matching inductor L1 with a Q of 15 or greater at 100MHz and minimal DC resistance.

 Select L1 inductor value to maximize resonance gain from FM frequency (88 MHz) to WB frequency

(~162 MHz)

 Place L1 and whip antenna close together and as far from potential noise sources as possible to reduce

capacitive and inductive coupling.

 Place the chip as close as possible to the whip antenna to minimize the antenna trace length. This reduces

parasitic capacitance and hence reduces coupling into the antenna by noise sources. This recommendation

must be followed for optimal device performance.

 Place ESD U3 as close as possible to the whip antenna for maximum effectiveness.

 Select ESD diode U3 with minimum capacitance.

 Place the ac coupling capacitor, C5, as close to the FMI pin as possible.

38

Rev. 0.8

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