nRF903 Nordic VLSI, nRF903 Datasheet - Page 20

• Manufacturer Part Number: nRF903
• Description: Multichannel RF Transceiver 433/868/915MHz
• Manufacturer: Nordic VLSI

PRODUCT SPECIFICATION
A well-designed PCB is necessary to achieve good RF performance. Keep in mind
that a poor layout may lead to loss of performance, or even functionality, if due care is
not taken. A fully qualified RF-layout for the nRF903 and its surrounding
components, including antennas and matching networks, can be downloaded from
.
A PCB with a minimum of two layers including a ground plane is recommended for
optimum performance. The nRF903 DC supply voltage should be decoupled as close
as possible to the VDD pins with high performance RF capacitors, see Table 19. It is
preferable to mount a large surface mount capacitor (e.g. 4.7 F tantalum) in parallel
with the smaller value capacitors. The nRF903 supply voltage should be filtered and
routed separately from the supply voltages of any digital circuitry.
Long power supply lines on the PCB should be avoided. All device grounds, VDD
connections and VDD bypass capacitors must be connected as close as possible to the
nRF903 IC. For a PCB with a topside RF ground plane, the VSS pins should be
connected directly to the ground plane. For a PCB with a bottom ground plane, the
best technique is to have via holes as close as possible to the VSS pads. One via hole
should be used for each VSS pin.
Full swing digital data or control signals should not be routed close to the PLL loop
filter components, the external VCO inductors or the power supply lines.
The placement of the VCO inductors is important. Optimum placement of the VCO
inductors yields a PLL loop filter voltage in the order of 1.8 ± 0.2V for the
868/915MHz bands and 2.2 ± 0.2V for the 433MHz band. The loopfilter voltage can
be measured at LF2 (pin 3). Figure 12 shows the recommended layout and inductor
placement for a PCB compatible with all three frequency bands. For 868MHz
operation, the inductors should be placed according to Figure 12 a., and for 433MHz
and 915MHz operation as shown in Figure 12 b. Please refer to the
section in the
chapter p. 16 regarding inductor specifications.
TM
See also the
chapter in the
section on the nRF
Support Pages.
L1
L2
L1
L2
VDD
VDD
Figure 12. Inductor placement for 868MHz and 433/915MHz operation.
Nordic VLSI ASA
-
Vestre Rosten 81, N-7075 Tiller, Norway
-
Phone [phone]
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Fax [phone]
Revision: 3.1
December 2002
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