nRF904 Nordic VLSI, nRF904 Datasheet - Page 11

• Manufacturer Part Number: nRF904
• Description: RF Transmitter 902-928MHz
• Manufacturer: Nordic VLSI

PRODUCT SPECIFICATION
A bias resistor R2 (see Figure 4) should be connected from the REXT pin to the
positive power supply VDD. The value of this resistor sets the output power level. See
table 9 for choice of R2 value.
Power setting resistor R2
RF output power
DC current consumption
47k
1dBm
18mA
-10dBm
9mA
120k
Conditions: VDD = 3.0V, VSS = 0V, T
= 27ºC, Load impedance = 400 .
A
Table 9. RF output power setting for the nRF904.
A well-designed PCB is necessary to achieve good RF performance. A PCB with a
minimum of two layers including a ground plane is recommended for optimum
performance.
The nRF904 DC supply voltage should be decoupled as close as possible to the VDD
pins with high performance RF capacitors, see Table 10. It is preferable to mount a
large surface mount capacitor (e.g. 4.7 F tantalum) in parallel with the smaller value
capacitors. The nRF904 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
nRF904 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 in or close to the VSS pads.
Full swing digital data or control signals should not be routed close to the crystal and
the XTAL pin.
Figure 11 shows a PCB layout example for the application schematic in Figure 10.
A double-sided FR-4 board of 1.6mm thickness is used. This PCB has a continuous
ground plane on the bottom layer. Additionally, there are ground areas on the
component side of the board to ensure sufficient grounding of critical components. A
large number of via holes connect the top layer ground areas to the bottom layer
ground plane. There is no ground plane beneath the antenna.
Nordic VLSI ASA
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Vestre Rosten 81, N-7075 Tiller, Norway
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Phone [phone]
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Fax [phone]
Revision: 2.1
October 2001
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