Si4430/31/32-B1
Rev 1.1 15
2. Functional Description
The Si4430/31/32 are ISM wireless transceivers with continuous frequency tuning over their specified bands which
encompasses from 240–960 MHz. The wide operating voltage range of 1.8–3.6 V and low current consumption
makes the Si4430/31/32 an ideal solution for battery powered applications.
The Si4430/31/32 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/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 then 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, output frequency and frequency
deviation at any frequency between 240–960 MHz. 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 Si4432’s PA output power can be configured between +1 and +20 dBm in 3 dB steps, while the Si4430/31's
PA output power can be configured between –8 and +13 dBm in 3 dB steps. The PA is single-ended to allow for
easy antenna matching and low BOM cost. The PA incorporates automatic ramp-up and rampdown control to
reduce unwanted spectral spreading. The +20 dBm power amplifier of the Si4432 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 Si4430/31/32 supports frequency hopping, TX/RX switch control, and antenna diversity switch
control to extend the link range and improve performance.
The Si4430/31/32 is designed to work with a microcontroller, crystal, and a few external components to create a
very low cost system as shown Figure 1. Voltage regulators are integrated on-chip which allows for a wide
operating supply voltage range from +1.8 to +3.6 V. A standard 4-pin SPI bus is used to communicate with an
external microcontroller. Three configurable general purpose I/Os are available. A complete list of the available
GPIO functions is shown in "8. Auxiliary Functions" on page 50 and includes microcontroller clock output, Antenna
Diversity, POR, and various interrupts.
The application shown in Figure 1 is designed for a system with a TX/RX direct-tie configuration without the use of
a TX/RX switch. Most lower power applications will use this configuration. A complete direct-tie reference design is
available from Silicon Laboratories applications support.
For applications seeking improved performance in the presence of multipath fading antenna diversity can be used.
Antenna diversity support is integrated into the Si4430/31/32 and can improve the system link budget by 8–10 dB
in the presence of these fading conditions, resulting in substantial range increases. A complete Antenna Diversity
reference design is available from Silicon Laboratories applications support.
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