si4430 Silicon Laboratories, si4430 Datasheet - Page 26

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

Si4430
3.6. Frequency Control
For calculating the necessary frequency register settings it is recommended to use the easy control window in
Silicon Labs’ Wireless Design Suite (WDS) or the Excel Calculator available on the product website. These
methods offer a simple method to quickly determine the correct settings based on the application requirements.
The following information can be used to calculated these values manually.
3.6.1. Frequency Programming
In order to receive or transmit an RF signal, the desired channel frequency, fcarrier, must be programmed into the
Si4430. Note that this frequency is the center frequency of the desired channel and not an LO frequency. The
carrier frequency is generated by a Fractional-N Synthesizer, using 20 MHz both as the reference frequency and
the clock of the (3
to obtain the desired frequency resolution of the synthesizer. The overall division ratio of the feedback loop consist
of an integer part (N) and a fractional part (F).In a generic sense, the output frequency of the synthesizer is:
The fractional part (F) is determined by three different values, Carrier Frequency (fc[15:0]), Frequency Offset
(fo[8:0]), and Frequency Modulation (fd[7:0]). Due to the fine resolution and high loop bandwidth of the synthesizer,
FSK modulation is applied inside the loop and is done by varying F according to the incoming data; this is
discussed further in "3.6.4. Frequency Deviation" on page 27. Also, a fixed offset can be added to fine-tune the
carrier frequency and counteract crystal tolerance errors. For simplicity assume that only the fc[15:0] register will
determine the fractional component. The equation for selection of the carrier frequency is shown below:
After selection of the fb (N) the fractional component may be solved with the following equation:
fb and fc are the actual numbers stored in the corresponding registers.
26
Add R/W Function/Description
73
74
75
76
77
R/W
R/W
R/W Frequency Band Select
R/W
R/W
Frequency Offset 1
Frequency Offset 2
Nominal Carrier
Nominal Carrier
Frequency 1
Frequency 0
rd
order) ΔΣ modulator. This modulator uses modulo 64000 accumulators. This design was made
fc
[
15
f
TX
fc[15]
:
fo[7]
fc[7]
D7
] 0


20



f
MHz
f
OUT
20
carrier
sbsel
fc[14]
fo[6]
fc[6]
Preliminary Rev. 0.4
D6
f
MHz
TX



20
20
(
fb
MHz
Reserved
MHz

[
fc[13]
: 4
fo[5]
fc[5]
D5
fb
] 0


[
: 4
(
(

N
N
24
] 0


fc[12]
fo[4]
fb[4]
fc[4]


D4
F
F
)
)
24
fc
64000
[
15




:
fc[11]
] 0
fo[3]
fb[3]
64000
fc[3]
D3
)
fc[10]
fo[2]
fb[2]
fc[2]
D2
fo[1] fo[0]
fo[9] fo[8]
fb[1] fb[0]
fc[9] fc[8]
fc[1] fc[0]
D1
D0 POR Def.
BBh
00h
00h
35h
80h