User Manual

Jennic
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Jennic
© Jennic 2008 JN-DS-JN5139 v1.5 81
• VCOTune circuit : The components defined in the schematic should be used in order to set the PLL bandwidth
correctly. It is also essential to keep these components close to the chip, with minimum track lengths.
B.3.13 Using a Balun
When using a single ended antenna, the wireless microcontroller will use a balun and should be connected as
indicated in Figure 56.
The tracks between IC1 pins RF+ and RF-, and the balanced side of the balun, are on the top layer. These are
impedance-controlled tracks, designed to provide the 200-ohm differential matched impedance required by the device
at its RF port. With the exception of the via connected to the VB_RF pin, other nearby tracks should be placed such
that there is at least three times the track width of unbroken ground on either side and underneath the tracks.
The other side of the balun should be connected to the antenna. This track is an unbalanced microstrip RF track
operating at 2.4 GHz. It should be impedance controlled to 50 ohms for a good RF input match.
Top View
BALUN
To wireless microcontroller
Track widths to
give 200 ohm
differential line
Track width
to give 50
ohm line
GND
GND
GND plane to be
cut underneath
differential tracks
Figure 56: Connecting the Balun
B.3.14 Decoupling Capacitors
Three capacitors should be used:
• Two ceramic 100-nF capacitors - one should be placed close to pin VDD1, the other should be placed close to
pin VDD2
• One 10-µF electrolytic capacitor connected to ground - if the PCB is a module then place this capacitor close to
the point where the power enters the module.