nRF903 Nordic VLSI, nRF903 Datasheet - Page 21

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

PRODUCT SPECIFICATION
The DATA pin is the input to the digital modulator of the transmitter while in TX-
mode, and demodulated data output while in RX-mode. The input signal to this pin
should be standard CMOS logic levels at 76.8kbit/s datarate.
The demodulated digital output data appear at the DATA-pin at standard CMOS logic
levels.
nRF903 uses GFSK modulation of data for optimum modulation bandwidth
efficiency. This type of modulation is an enhanced version of FSK in which each of
the two logic levels corresponds to a frequency value;
In Gaussian Frequency Shift Keying (GFSK), the data is filtered through a gaussian
filter before modulating the carrier. Figure 13 shows the general principle. This results
in a narrower power spectrum of the modulated signal, which in turn allows a higher
bitrate to be transferred in the same channel bandwidth. This is often referred to as
bandwidth efficiency, and is given in bits/Hz. The nRF903 bandwidth efficiency is
thus 0.5 bit/Hz. Figure 14 shows the difference between the nRF903 GFSK output
spectrum and a comparable FSK-spectrum at 76.8kbit/s. It should also be noted that a
GFSK system
of destructive interference in a system with multiple nodes.
Gaussian Minimum Shift Keying (GMSK) is the term used for a GFSK signal where
the bitrate is four times the frequency deviation.
Nordic VLSI ASA
Revision: 3.1
DATA
DATA
Figure 13. Principle of Gaussian filtering of transmitted data
FSK
FSK
-
f
= “1”
= “0”
centre
frequency
DATA logic
f
f
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’1’
’0’
’1’
’0’
level
f
f
’1’
’0’
= f
= f
centre
centre
+ f
- f
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Phone [phone]
and thus reduces the risk
time
time
-
Fax [phone]
December 2002