Si1000/1/2/3/4/5
Frequency Correction
RX
AFC disabled
AFC enabled
23.3.8. TX Data Rate Generator
The data rate is configurable between 0.123–256 kbps. For data rates below 30 kbps the ”txdtrtscale” bit in
register 70h should be set to 1. When higher data rates are used this bit should be set to 0.
The TX date rate is determined by the following formula in bps:
DR_TX (bps) =
txdr
15:0
1 MHz
------------------------------------------------
-
16 + 5
txdtrtscale
2
DR_TX(bps)
2
txdr[15:0] = --------------------------------------------------------------------------------
-
1 MHz
16 + 5
txdtrtscale
TX
Freq Offset Register
Freq Offset Register
Freq Offset Register
AFC
For data rates higher than 100 kbps, Register 58h should be changed from its default of 80h to C0h. Non-
optimal modulation and increased eye closure will result if this setting is not made for data rates higher
than 100 kbps. The txdr register is only applicable to TX mode and does not need to be programmed for
RX mode. The RX bandwidth which is partly determined from the data rate is programmed separately.
Add R/W
6E
6F
Function/
Description
D7
D6
D5
D4
D3
D2
D1
D0
POR Def.
R/W TX Data Rate 1
R/W TX Data Rate 0
txdr[15]
txdr[7]
txdr[14] txdr[13] txdr[12] txdr[11]
txdr[6]
txdr[5]
txdr[4]
txdr[3]
txdr[10]
txdr[2]
txdr[9]
txdr[1]
txdr[8]
txdr[0]
0Ah
3Dh
23.4. Modulation Options
23.4.1. Modulation Type
The EZRadioPRO transceivers support three different modulation options: Gaussian Frequency Shift Key-
ing (GFSK), Frequency Shift Keying (FSK), and On-Off Keying (OOK). GFSK is the recommended modu-
lation type as it provides the best performance and cleanest modulation spectrum. Figure 23.6
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.
modtyp[1:0]
00
01
10
11
Modulation Source
Unmodulated Carrier
OOK
FSK
GFSK (enable TX Data CLK when direct mode is used)
Rev. 1.0
251
SILABS [ SILICON LABORATORIES ]
