SI4438 Datasheet, PDF (11/44 Pages) Silicon Laboratories – Low active power consumption

Si4438
2. Functional Description
The Si4438 devices are high-performance, low-current, wireless ISM transceivers that cover the sub-GHz bands.
The wide operating voltage range of 1.8–3.6 V and low current consumption make the Si4438 an ideal solution for
battery powered applications. The Si4438 operates as a time division duplexing (TDD) transceiver where the
device alternately transmits and receives data packets. The device uses a single-conversion mixer to downconvert
the 2-level FSK/GFSK or OOK modulated receive signal to a low IF frequency. Following a programmable gain
amplifier (PGA) the signal is converted to the digital domain by a high performance  ADC allowing filtering,
demodulation, slicing, and packet handling to be performed in the built-in DSP increasing the receiver’s
performance and flexibility versus analog based architectures. The demodulated signal is output to the system
MCU through a programmable GPIO or via the standard SPI bus by reading the 64-byte RX FIFO.
A single high precision local oscillator (LO) is used for both transmit and receive modes since the transmitter and
receiver do not operate at the same time. The LO is generated by an integrated VCO and  Fractional-N PLL
synthesizer. The synthesizer is designed to support configurable data rates from 100 bps to 500 kbps. The transmit
FSK data is modulated directly into the  data stream and can be shaped by a Gaussian low-pass filter to reduce
unwanted spectral content.
The Si4438 contains a power amplifier (PA) that supports output power up to +20 dBm with very high efficiency,
consuming only 75 mA. The integrated +20 dBm power amplifier can also be used to compensate for the reduced
performance of a lower cost, lower performance antenna or antenna with size constraints due to a small
form-factor. Competing solutions require large and expensive external PAs to achieve comparable performance.
The PA is single-ended to allow for easy antenna matching and low BOM cost. The PA incorporates automatic
ramp-up and ramp-down control to reduce unwanted spectral spreading. The Si4438 family supports TX/RX switch
control, and antenna diversity switch control to extend the link range and improve performance. Built-in antenna
diversity can be used to further extend range and enhance performance. Antenna diversity is completely integrated
into the Si4438 and can improve the system link budget by 8–10 dB, resulting in substantial range increases under
adverse environmental conditions. A highly configurable packet handler allows for autonomous encoding/decoding
of nearly any packet structure. Additional system features, such as an automatic wake-up timer, low battery
detector, 64 byte TX/RX FIFOs, and preamble detection, reduce overall current consumption and allows for the
use of lower-cost system MCUs. An integrated temperature sensor, power-on-reset (POR), and GPIOs further
reduce overall system cost and size. The Si4438 is designed to work with an MCU, crystal, and a few passive
components to create a very low-cost system.
Rev 1.0
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