AN851 Datasheet, PDF (11/25 Pages) Silicon Laboratories – Si468X SCHEMATICS AND LAYOUT GUIDE

AN851
5. Ferrite Loop Antenna for AM Receive on AMI
There are two types of antenna that will work well for an AM receiver: a ferrite loop antenna or an air loop antenna.
A ferrite loop antenna can be placed internally on the device or externally to the device with a wire connection.
When the ferrite loop antenna is placed internally on the device, it is more susceptible to picking up any noise
within the device. When the ferrite loop antenna is placed outside a device, e.g., at the end of an extension cable,
it is less prone to device noise activity and may result in better AM reception.
5.1. Ferrite Loop Antenna Design
Figure 7 shows an example of ferrite loop antennas. The left figure is the standard size ferrite loop antenna. It is
usually used in products with a lot of space, such as desktop radios. The right figure is the miniature size of the
loop antenna. It is usually used in small products where space is at a premium, such as cell phones. If possible,
use the standard size ferrite loop antenna as it has a better sensitivity than the miniature one.
Figure 7. Standard and Miniature Ferrite Loop Antennas
A loop antenna with a ferrite inside should be designed such that the inductance of the ferrite loop is between 180
and 450 µH for the Si468x AM Receiver.
Table 5 lists the recommended ferrite loop antenna for the Si468x AM Receiver.
5.2. Ferrite Loop Antenna Schematic
Figure 8. AM Ferrite Loop Antenna Schematic
D1 is an optional ESD diode if there is an exposed pad going to the AMI pin.
Rev. 0.2
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