si4430 Silicon Laboratories, si4430 Datasheet - Page 48

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

Si4430
7.1.1. Advanced FSK and GFSK Settings
In nearly all cases, the information in Table 16, “RX Modem Configurations for FSK and GFSK,” on page 47 can be
used to determine the required FSK and GFSK modem parameters. The section includes a more detailed
discussion of the various modem parameters to allow for experienced designers to further configure the modem
performance.
In FSK or GFSK mode the receiver can handle a wide range of modulation indices ranging from 0.5 up to 32. The
modulation index (h) is defined by the following:
When the modulation index is 1 or higher the modulation bandwidth can be approximated by the following
equation:
When the modulation index is lower than 1 the modulation bandwidth can be approximated by the following:
Where BW
frequency deviation of the received GFSK/FSK signal in kHz and enmanch is the Manchester Coding parameter
(see Reg. 70h, enmach is 1 when Manchester coding is enabled, enmanch is 0 when disabled).
The bandwidth of the channel select filter in the receiver might need some extra bandwidth to cope with tolerances
in transmit and receive frequencies which depends on the tolerances of the applied crystals. When the relative
frequency error (F
the AFC will correct the frequency error without needing extra bandwidth. When the frequency error exceeds
BW
When the AFC is enabled it is recommended to set the bandwidth of the channel select filter (BW
to the formulas below:
When the AFC is disabled it is recommended to set the bandwidth of the channel select filter (BW
to the following:
When the required bandwidth (BW) is calculated then the three filter parameters, ndec_exp, dwn3_bypass and
filset, can be found from the table below. When the calculated bandwidth value is not exactly available then select
the higher available bandwidth closest to the calculated bandwidth.
48
mod
/2 then some extra bandwidth will be needed to assure proper AFC operation under worst case conditions.
mod
is an approximation of the modulation bandwidth in kHz, Rb is the payload bit rate in kbps, Fd is the
error
) between transmitter and receiver is less than half the modulation bandwidth (BW
BW
F
F
BW
error
error
mod
BW
mod



h



BW
BW
ch


Rb

Preliminary Rev. 0.4
2

sel
2
2
Rb
Rb
mod
mod





1

BW



1

1
2


enmanch
BW
BW

mod
enmanch
enmanch
Fd
ch
ch



2
sel
sel



F


error
2


BW

2


Fd
F
mod
Fd
error




ch-sel
ch-sel
) according
) according
mod
) then