SI4438 Datasheet, PDF (19/44 Pages) Silicon Laboratories – Low active power consumption

Si4438
4. Modulation and Hardware Configuration Options
The Si4438 supports three different modulation options and can be used in various configurations to tailor the
device to any specific application or legacy system for drop in replacement. The modulation and configuration
options are set in property, MODEM_MOD_TYPE. Refer to the EZRadioPRO API Documentation.zip file available
on www.silabs.com for details.
4.1. Modulation Types
The Si4438 supports five different modulation options: Gaussian frequency shift keying (GFSK), frequency-shift
keying (FSK), on-off keying (OOK). Minimum shift keying (MSK) can also be created by using GFSK settings.
GFSK is the recommended modulation type as it provides the best performance and cleanest modulation
spectrum. The modulation type is set by the “MOD_TYPE[2:0]” registers in the “MODEM_MOD_TYPE” API
property. A continuous-wave (CW) carrier may also be selected for RF evaluation purposes. The modulation
source may also be selected to be a pseudo-random source for evaluation purposes.
4.2. Hardware Configuration Options
There are different receive demodulator options to optimize the performance and mutually-exclusive options for
how the RX/TX data is transferred from the host MCU to the RF device.
4.2.1. Receive Demodulator Options
There are multiple demodulators integrated into the device to optimize the performance for different applications,
modulation formats, and packet structures. The calculator built into WDS will choose the optimal demodulator
based on the input criteria.
4.2.1.1. Synchronous Demodulator
The synchronous demodulator's internal frequency error estimator acquires the frequency error based on a
101010 preamble structure. The bit clock recovery circuit locks to the incoming data stream within four transactions
of a “10” or “01” bit stream. The synchronous demodulator gives optimal performance for 2-level FSK or GFSK
modulation that has a modulation index less than 2.
4.2.1.2. Asynchronous Demodulator
The asynchronous demodulator should be used OOK modulation and for FSK/GFSK under one or more of the
following conditions:
Modulation index > 2
Non-standard preamble (not 1010101... pattern)
When the modulation index exceeds 2, the asynchronous demodulator has better sensitivity compared to the
synchronous demodulator. An internal deglitch circuit provides a glitch-free data output and a data clock signal to
simplify the interface to the host. There is no requirement to perform deglitching in the host MCU. The
asynchronous demodulator will typically be utilized for legacy systems and will have many performance benefits
over devices used in legacy designs. Unlike the Si4432/31 solution for non-standard packet structures, there is no
requirement to perform deglitching on the data in the host MCU. Glitch-free data is output from Si4438 devices,
and a sample clock for the asynchronous data can also be supplied to the host MCU; so, oversampling or bit clock
recovery is not required by the host MCU. There are multiple detector options in the asynchronous demodulator
block, which will be selected based upon the options entered into the WDS calculator. The asynchronous
demodulator's internal frequency error estimator is able to acquire the frequency error based on any preamble
structure.
4.2.2. RX/TX Data Interface With MCU
There are two different options for transferring the data from the RF device to the host MCU. FIFO mode uses the
SPI interface to transfer the data, while direct mode transfers the data in real time over GPIO.
4.2.2.1. FIFO Mode
In FIFO mode, the transmit and receive data is stored in integrated FIFO register memory. The TX FIFO is
accessed by writing Command 66h followed directly by the data/clk that the host wants to write into the TX FIFO.
The RX FIFO is accessed by writing command 77h followed by the number of clock cycles of data the host would
like to read out of the RX FIFO. The RX data will be clocked out onto the SDO pin.
Rev 1.0
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