Transcript
Design Note AMB8425 Version 1.0
Common layout guidelines Please pay attention to the following advices during the design-in process of the AMB8425:
Underneath the radio module the top layer of your PCB should be kept free from traces and vias due to the fact the AMB8425 it is only covered with solder resist and the vias are not covered at all.
Traces on other layers underneath the module should be avoided. If required, the traces should be shielded by a ground plane.
A blocking capacitor for the supply voltage is recommended (e.g. 100 µF Tantal). Place this capacitor as close as possible to the radio module.
Antenna connection The antenna trace has to be designed as a 50 Ohm feed line.
Figure 1 Dimensioning the antenna feed line as micro strip
The width W can be calculated using equation 1: 5.98 H W 1.25 50 1.41 Tmet r 87 e Equation 1 Parameters of the antenna feeding line
Example: a FR4 material with r = 4.3, a height H = 1000 µm and a copper thickness of Tmet= 18 µm will lead to a trace width of W ~ 1.9 mm. Around the micro strip line a clearance of 2 mm to the next PCB traces or other components should be kept. Place a ground plane on the bottom layer / on the next layer below the feeding line. Keep the feeding line as short as possible.
Design Note AMB8425
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Released: 21.06.2011
The feeding line should be designed with an optional PI element (capacitor C1 to ground, coil L1 in series and capacitor C2 to ground) in order to realize antenna adjustments and / or filter functions. If the filter is not used, L1 can be replaced by a 68 pF capacitor (see Figure 2). A simple but effective antenna solution is an 8,6 cm long wire, a Lambda/4 antenna. This wire should point away from the module and needs a ground plane below the feeding point. The antenna should have a minimum distance of 3,1 cm to any other metal or conductive material.
Figure 2 Matching circuit of a λ/4 antenna
When using metallic, metalized or conductive material for the system’s housing, please consider that these materials are impenetrable or at least can cause a strong attenuation of radio waves. In that case, the antenna has to be placed outside of the enclosure. The RF there for is led through a 50 Ohm trace towards a RF connector (e.g. BNC, SMA, GSC or U.FL). This connector could directly break through the enclosure (for example SMA-/BNC right angle connectors, Figure 3) or led the RF outwards through a pre-assembled cable (for example GSC to SMA, Figure 4).
Figure 3 Enclosure break through with BNC-connector right angle
Design Note AMB8425
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Figure 4 GSC-SMA-Adapter
AMBER wireless offers with AMB1981 (Dipole-Antenna) and AMB1982 (MonopoleAntenna with magnet foot and 1.5m antenna cable) qualified solutions for the 868 MHz frequency range. Both types have SMA male connectors.
Figure 5 AMB1981: 868 MHz Dipole-Antenna
Figure 6 AMB1982: 868 MHz magnet foot antenna with 1.5 m antenna cable
Keep in mind that every external monopole antenna needs a counterpoise (a ground plane at the feeding point). Omitting this counterpoise will lead to a reduced range!
Design Note AMB8425
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Released: 21.06.2011
Dimensions 8
0,8
3 1
1
1
13,5
1
27
0,8
Ø1
1,5
13
1,5
16
Figure 7 Dimensions [mm], height approx. 3.5 mm
1
1
1
1
3
27
Footprint
2
13
2
17
Figure 8 Footprint [mm]
Design Note AMB8425
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Released: 21.06.2011
Pin Assignment (Top view)
Pad-Name VCC GND ANTENNA UTXD, URXD /RTS /DATA_INDICATE /DATA_REQUEST SLEEP, TRX_DISABLE /CONFIG * /RESET
Function Positive supply voltage Common Antenna connection UART transmit , UART receive Ready to send/receive Signals incoming data Starts transmitting Selection of low-power mode Change into command-mode Reset-Input
Figure 9 Pin out
Design Note AMB8425
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Released: 21.06.2011
