SI4468-7 Datasheet, PDF (14/57 Pages) Silicon Laboratories – Highly configurable packet handler

Si4468/7
2. Functional Description
The Si446x devices are high-performance, low-current, wireless ISM transceivers that cover the sub-GHz bands.
A key feature of the Si4468/7 is the support for IEEE 802.15.4g PHY and some features of 802.15.4 above the
physical layer, which enables low-power, long-range networking solutions including mesh networking. In
conjunction with Silicon Labs industry-leading ZigBee SoCs and EFM32 energy-friendly 32-bit ARM based
microcontrollers, the Si4468/7 enables low-power solutions from sub GHz to 2.4 GHz for various “Internet of
Things” applications.
The wide operating voltage range of 1.8–3.8 V and low current consumption make the Si446x an ideal solution for
battery powered applications. The Si446x 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 2/4-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 1 Mbps. The Si4468/7
operate in the frequency bands of 142–175, 283–350, 350–525, and 850–1050 MHz with a maximum frequency
accuracy step size of 28.6 Hz. 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 Si4468 contains a power amplifier (PA) that supports output power up to +20 dBm with very high efficiency,
consuming only 70 mA at 169 MHz and 85 mA at 915 MHz. 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 Si4467 is designed to support single coin cell operation with current consumption
below 18 mA for +10 dBm output power. Two match topologies are available for the Si4467: Class-E and
switched-current. Class-E matching provides optimal current consumption, while switched-current matching
demonstrates the best performance over varying battery voltage and temperature with slightly higher current
consumption. 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 Si446x family supports
frequency hopping, TX/RX switch control, and antenna diversity switch control to extend the link range and
improve performance. Built-in antenna diversity and support for frequency hopping can be used to further extend
range and enhance performance. Antenna diversity is completely integrated into the Si446x 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
Si446x is designed to work with an MCU, crystal, and a few passive components to create a very low-cost system.
2.1. Boot Modes
The Si4468/7 has two boot modes. One boot mode supports 802.15.4 functionality to enable standards-based,
sub-GHz mesh networking with support for 802.15.4 MR-FSK PHY (15.4g) and key MAC (15.4) features. The
second boot mode supports legacy Si4463/1/0 compatibility and is intended to support proprietary solutions that
require additional flexibility in configuring the device. The legacy boot mode is called EZRadioPRO boot mode.
This mode is software- and hardware-compatible with Si4463/1/0 and also supports 802.15.4g PHY and WMBus
operation. The boot mode selection is done using the POWER_UP command and is described in the API
documentation.
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. Figure 2 demonstrates an application for +20 dBm using an external T/R-switch.
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Rev 1.0