EM351-RTR Ember, EM351-RTR Datasheet - Page 29

• Manufacturer Part Number: EM351-RTR
• Description: IC RF TXRX ZIGBEE 128KB 48QFN
• Manufacturer: Ember

Specifications of EM351-RTR

• Frequency: 2.4GHz
• Data Rate - Maximum: 250kbps
• Modulation Or Protocol: 802.15.4 Zigbee
• Power - Output: 3dBm
• Sensitivity: -100dBm
• Voltage - Supply: 2.1 V ~ 3.6 V
• Current - Receiving: 26mA
• Current - Transmitting: 31mA
• Data Interface: PCB, Surface Mount
• Memory Size: 128kB Flash, 12kB RAM
• Antenna Connector: PCB, Surface Mount
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 48-QFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Applications: -
• Other names: 636-1010-2

4
4.1
4.2
Radio Module
Receive (Rx) Path
Transmit (Tx) Path
The radio module consists of an analog front end and digital baseband as shown in Figure 3-1, EM35x Block
Diagram in Chapter 3, Top Level Functional Description.
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 EM35x’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
The EM35x 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.
4.1.2
The EM35x calculates the RSSI over every 8-symbol period as well as at the end of a received packet. The
linear range of RSSI is specified to be at least 40 dB over temperature. At room temperature, the linear range
is approximately 60 dB (-90 dBm to -30 dBm input signal).
The EM35x Rx baseband provides support for the IEEE 802.15.4-2003 RSSI CCA method. Clear channel reports
busy medium if RSSI exceeds its threshold.
The EM35x Tx path produces an O-QPSK-modulated signal using the analog front end and digital baseband. The
area- and power-efficient Tx architecture uses a two-point modulation scheme to modulate the RF signal
generated by the synthesizer. The modulated RF signal is fed to the integrated PA and then out of the EM35x.
4.2.1
The EM35x Tx baseband in the digital domain spreads the 4-bit symbol into its IEEE 802.15.4-2003-defined 32-
chip sequence. It also provides the interface for the Ember software to calibrate the Tx module to reduce
silicon process, temperature, and voltage variations.
4.2.2
For applications requiring an external PA, two signals are provided called TX_ACTIVE and nTX_ACTIVE. These
signals are the inverse of each other. They can be used for external PA power management and RF switching
logic. In transmit mode the Tx baseband drives TX_ACTIVE high, as described in Table 7-5, GPIO Signal
Assignments. In receive mode the TX_ACTIVE signal is low. TX_ACTIVE is the alternate function of PC5, and
Rx Baseband
RSSI and CCA
Tx Baseband
TX_ACTIVE and nTX_ACTIVE Signals
Final
4-1
EM351 / EM357
120-035X-000G