
EM358x
Rev. 0.4
33
4 Radio Module
The radio module consists of an analog front end and digital baseband as shown in Figure 4-1.
Figure 4-1. EM358 Block Diagram
4.1 Receive (Rx) Path
The Rx path uses a low-IF, super-heterodyne receiver that rejects the image frequency using complex mixing and
polyphase filtering. In the analog domain, the input RF signal from the antenna is first amplified and mixed down
to a 4 MHz IF frequency. The mixers’ output is filtered, combined, and amplified before being sampled by a 12
MSPS ADC. The digitized signal is then demodulated in the digital baseband. The filtering within the Rx path
improves the EM358x’s co-existence with other 2.4 GHz transceivers such as Zigbee/ 802.15.4-2003, IEEE
802.11-2007, and Bluetooth radios. The digital baseband also provides gain control of the Rx path, both to enable
the reception of small and large wanted signals and to tolerate large interferers.
4.1.1
Rx Baseband
The EM358x Rx digital baseband implements a coherent demodulator for optimal performance. The baseband
demodulates the O-QPSK signal at the chip level and synchronizes with the IEEE 802.15.4-2003-defined
preamble. An automatic gain control (AGC) module adjusts the analog gain continuously every ¼ symbol until the
preamble is detected. Once detected, the gain is fixed for the remainder of the packet. The baseband despreads
the demodulated data into 4-bit symbols. These symbols are buffered and passed to the hardware-based MAC
module for packet assembly and filtering.
In addition, the Rx baseband provides the calibration and control interface to the analog Rx modules, including
the LNA, Rx baseband filter, and modulation modules. The Ember software includes calibration algorithms that
use this interface to reduce the effects of silicon process and temperature variation.
Summary of Contents for EMBER EM358 series
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