SI4721 datasheet(49/69 Pages) SILABS

49 / 69 page

AN383

Rev. 0.8

10.4. SW 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 the whip

antenna away from any sources of interference and away from the I/O signals of the Si4734/35. Place the ac

coupling capacitor, C8, as close to the AMI pin as possible. Place the ac coupling capacitor, C1, as close as

possible to the FMI pin. Place ESD diodes U2 and U3 as close as possible to the whip antenna input connector for

maximum effectiveness.

10.5. SW Whip Antenna Design Checklist



Maximize whip antenna length for optimal performance.



Select matching inductor L1 with a Q of 20 or greater at 25 MHz and minimal dc resistance.



Select L1 inductor value to maximize signal strength across the FM band.



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 diodes U2 and U3 as close as possible to the whip antenna for maximum effectiveness.



Select ESD diodes U2 and U3 with minimum capacitance.



Place the ac coupling capacitor, C8, as close to the AMI pin as possible.



Follow the design checklist in "8. Ferrite Loop Antenna for AM/LW Receive on AMI (Si4730/31/34/35/36/37

Only)" on page 39 for the ferrite antenna to optimize AM performance (if AM is used in addition to SW).

SI4721 Datasheet(PDF) 49 Page - Silicon Laboratories