nRF904 Nordic VLSI, nRF904 Datasheet - Page 6

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

PRODUCT SPECIFICATION
ASK modulation can be realised by using the REXT pin (see Figure 4). When R2 is
connected to VDD, the chip transmits a carrier. When R2 is connected to GND then
the internal output power amplifier is turned off. These two situations represent logic
‘1’ and logic ‘0’ in an ASK system. When ASK modulation is used, the DIN pin must
be connected to VDD.
Clock mode is available so that an external microprocessor may have a reference
signal without the cost of a second crystal. In Clock mode, the crystal oscillator and
reference clock output, XO8, are operating, while the rest of the transmitter is
disabled.
Connecting the power-adjusting resistor R2 to ground sets clock mode. Current
consumption in Clock mode is typically 175 A when no load is applied at the XO8
clock output pin. If a capacitive load is applied at the XO8 output, then current
consumption in Clock mode will increase. Start-up time when switching between
Clock mode and Transmit mode is extremely fast, less than 50 s.
The frequency of the clock signal is 1/8th of the crystal frequency i.e. a crystal
frequency of 14.2992 MHz will result in an output clock frequency of 1.7874 MHz.
The XO8 output is an open collector with an internal 30 k resistor.
The internal XO8 series resistor has a typical value of 30 k . For a given value of the
external resistor R3 the output voltage V
Nordic VLSI ASA
Revision: 2.1
DATA
R41=3.9k
R42=22k
Figure 5. Alternative external DIN components for setting the spectral bandwidth.
a) 1st Order external filter
3dB frequency = 50kHz
R41
-
C41=680pF
Vestre Rosten 81, N-7075 Tiller, Norway
8
R42
C41
DIN
3
R43=680
R44=3.9k
R45=22k
DATA
b) 2nd Order external filter
QhtrÃ%Âsà %
30
XO8
3
3dB frequency = 45kHz
(peak-to-peak) may be calculated as:
R43
-
Phone [phone]
C42=3.3nF
C43=330pF
C42
R44
[Vpp]
C43
R45
-
Fax [phone]
DIN
October 2001