si4430 Silicon Laboratories, si4430 Datasheet - Page 32

• Manufacturer Part Number: si4430
• Description: Si4430 Ism Transceiver
• Manufacturer: Silicon Laboratories

Si4430
4. Modulation Options
4.1. Modulation Type
The Si4430 supports three different modulation options: Gaussian Frequency Shift Keying (GFSK), Frequency
Shift Keying (FSK), and On-Off Keying (OOK). GFSK is the recommended modulation type as it provides the best
performance and cleanest modulation spectrum. Figure 11 demonstrates the difference between FSK and GFSK
for a Data Rate of 64 kbps. The time domain plots demonstrate the effects of the Gaussian filtering. The frequency
domain plots demonstrate the spectral benefit of GFSK over FSK. The type of modulation is selected with the
modtyp[1:0] bits in "Register 71h. Modulation Mode Control 2". Note that it is also possible to obtain an
unmodulated carrier signal by setting modtyp[1:0] = 00.
32
TX Modulation Time Domain Waveforms -- FSK vs. GFSK
-0.5
-1.0
-1.5
-0.5
-1.0
1.5
1.0
0.5
0.0
1.0
0.5
0.0
0
50
100
modtyp[1:0]
150
200
00
01
10
11
time, usec
250
300
Figure 11. FSK vs GFSK Spectrums
GFSK (enable TX Data CLK when direct mode is used)
350
400
450
Preliminary Rev. 0.4
500
Unmodulated Carrier
Modulation Source
-100
-100
TX Modulation Spectrum -- FSK vs GFSK (Continuous PRBS)
-20
-40
-60
-80
-20
-40
-60
-80
-250
OOK
FSK
DataRate
-200
64000.0
-150
-100
TxDev
32000.0
-50
freq, KHz
0
BT_Filter
50
0.5
100
ModIndex
150
1.0
200
250