EM250-RTR Ember, EM250-RTR Datasheet - Page 17

• Manufacturer Part Number: EM250-RTR
• Description: IC ZIGBEE SYSTEM-ON-CHIP 48-QFN
• Manufacturer: Ember
• Series: EM250r

Specifications of EM250-RTR

• Frequency: 2.4GHz
• Modulation Or Protocol: 802.15.4 Zigbee
• Applications: Home/Building Automation, Industrial Control and Monitoring
• Power - Output: 3dBm
• Sensitivity: -97dBm
• Voltage - Supply: 2 V ~ 3.6 V
• Current - Receiving: 35.5mA
• Current - Transmitting: 33mA
• Data Interface: PCB, Surface Mount
• Memory Size: 128kB Flash, 5kB SRAM
• Antenna Connector: PCB, Surface Mount
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 48-QFN
• For Use With: 636-1009 - PROGRAMMER USB FLASH EM250/260
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Data Rate - Maximum: -
• Other names: 636-1000-2

4 Functional Description—System Modules
4.1
4.2
Receive (RX) Path
Transmit (TX) Path
The EM250 contains a dual-thread mode of operation—System Mode and Application Mode—to guarantee mi-
crocontroller bandwidth to the application developer and protect the developer from errant software access.
During System Mode, all areas including the RF Transceiver, MAC, Packet Trace Interface, Sleep Timer, Power
Management Module, Watchdog Timer, and Power on Reset Module are accessible.
Since the EM250 comes with a license to EmberZNet, the Ember ZigBee-compliant software stack, these areas
are not available to the application developer in Application Mode. The following brief description of these
modules provides the necessary background on the operation of the EM250. For more information, contact
www.ember.com/support.
The EM250 RX path spans the analog and digital domains. The RX architecture is based on a low-IF, super-
heterodyne receiver. It utilizes differential signal paths to minimize noise interference. The input RF signal is
mixed down to the IF frequency of 4MHz by I and Q mixers. The output of the mixers is filtered and combined
prior to being sampled by a 12Msps ADC. The RX filtering within the RX path has been designed to optimize the
co-existence of the EM250 with other 2.4GHz transceivers, such as the IEEE 802.11g and Bluetooth.
4.1.1
The EM250 RX baseband (within the digital domain) implements a coherent demodulator for optimal perform-
ance. The baseband demodulates the O-QPSK signal at the chip level and synchronizes with the IEEE 802.15.4-
2003 preamble. Once a packet preamble is detected, it de-spreads the demodulated data into 4-bit symbols.
These symbols are buffered and passed to the hardware-based MAC module for filtering.
In addition, the RX baseband provides the calibration and control interface to the analog RX modules, includ-
ing the LNA, RX Baseband Filter, and modulation modules. The EmberZNet software includes calibration algo-
rithms which use this interface to reduce the effects of process and temperature variation.
4.1.2
The EM250 calculates the RSSI over an 8-symbol period as well as at the end of a received packet. It utilizes
the RX gain settings and the output level of the ADC within its algorithm.
The EM250 RX baseband provides support for the IEEE 802.15.4-2003 required CCA methods summarized in
Table 10. Modes 1, 2, and 3 are defined by the 802.15.4-2003 standard; Mode 0 is a proprietary mode.
CCA Mode
0
1
2
3
The EM250 transmitter utilizes both analog circuitry and digital logic to produce the O-QPSK modulated signal.
The area-efficient TX architecture directly modulates the spread symbols prior to transmission. The differen-
tial signal paths increase noise immunity and provide a common interface for the external balun.
RX Baseband
RSSI and CCA
Mode Behavior
Clear channel reports busy medium if either carrier sense OR RSSI exceeds their thresholds.
Clear channel reports busy medium if RSSI exceeds its threshold.
Clear channel reports busy medium if carrier sense exceeds its threshold.
Clear channel reports busy medium if both RSSI AND carrier sense exceed their thresholds.
Table 10. CCA Mode Behavior
120-0082-000I
EM250
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