SN260 datasheet(15/88 Pages) STMICROELECTRONICS

15 / 88 page

SN260

Functional description

15/88

Functional description

The SN260 connects to the Host micro controller through a standard SPI interface. The

EmberZNet Serial Protocol (EZSP) has been defined to allow an application to be written on

a host micro controller of choice. Therefore, the SN260 comes with a license to EmberZNet,

the EmberZNet ZigBee-compliant software stack. The following brief description of the

hardware modules provides the necessary background on the operation of the SN260. For

more information, contact your local ST sales representative.

5.1

Receive (RX) path

The SN260 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 SN260 with other 2.4GHz transceivers, such as the IEEE 802.11g and

Bluetooth.

5.1.1

RX baseband

The SN260 RX baseband (within the digital domain) 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 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, including the LNA, RX Baseband Filter, and modulation modules. The EmberZNet

software includes calibration algorithms which use this interface to reduce the effects of

process and temperature variation.

5.1.2

RSSI and CCA

The SN260 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 SN260 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.

Table 10.

CCA mode behavior

CCA mode

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.

SN260 Datasheet(PDF) 15 Page - STMicroelectronics

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