si4330 Silicon Laboratories, si4330 Datasheet - Page 23

• Manufacturer Part Number: si4330
• Description: Si4330 Ism Receiver
• Manufacturer: Silicon Laboratories

3.6. Frequency Control
For calculating the necessary frequency register settings it is recommended that customers 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 an RF signal, the desired channel frequency, fcarrier, must be programmed into the Si4330.
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 10 MHz both as the reference frequency and the clock
of the (3
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 25. 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:
The integer part (N) is determined by fb[4:0]. Additionally, the frequency can be halved by connecting a ÷2 divider
to the output. This divider is not inside the loop and is controlled by the hbsel bit in "Register 75h. Frequency Band
Select". This effectively partitions the entire 240–960 MHz frequency range into two separate bands: High Band
(HB) for hbsel = 1, and Low Band (LB) for hbsel = 0. The valid range of fb[4:0] is from 0 to 23. If a higher value is
written into the register, it will default to a value of 23. The integer part has a fixed offset of 24 added to it as shown
in the formula above. Table 11 demonstrates the selection of fb[4:0] for the corresponding frequency band.
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.
Add R/W Function/Description
73
74
75
76
77
R/W
R/W
R/W Frequency Band Select Reserved
R/W
R/W
rd
order) ΔΣ modulator. This modulator uses modulo 64000 accumulators. This design was made to obtain
Frequency Offset 1
Frequency Offset 2
Nominal Carrier
Nominal Carrier
Frequency 1
Frequency 0
fc
f
[
15
TX
:

] 0
10
Reserved Reserved Reserved Reserved Reserved Reserved fo[9] fo[8]
fc[15]

fo[7]
fc[7]
MHz
f
D7
carrier

 

10
MHz
( *

f
OUT
10
hbsel
sbsel
fc[14]
fo[6]
fc[6]
D6
Preliminary Rev 0.2
( *
MHz
f

TX
hbsel
10

) 1
MHz

(
( *
fc[13]
hbsel
fo[5]
fc[5]
hbsel

D5
) 1
fb

[
(

: 4
N

fb
) 1
] 0

fc[12]
[
fo[4]
fb[4]
fc[4]
D4
: 4
F


(
)
24
] 0
N



24
F
fc
fc[11]
fo[3]
fb[3]
64000
fc[3]
)
D3
[

 

15
*
64000
:
] 0
)
fc[10]
fo[2]
fb[2]
fc[2]
D2
fo[1] fo[0]
fb[1] fb[0]
fc[9] fc[8]
fc[1] fc[0]
D1
Si4330
D0 POR Def.
BBh
00h
00h
35h
80h
23