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Wireless MCU puts 802.15.4 RF on single chip

Atmel describes its ATmega128RFA1 IC as a wireless MCU (microcontroller); the die hosts a version of its picoPower AVR RISC embedded-flashbased MCU, together with a 2.4-GHz transceiver, for applications such as ZigBee and 6LoWPAN. The RF block is IEEE 802.15.4-compliant and features a link budget of 103.5 dB, comprising a receiver sensitivity of 100 dBm and a transmitter output power of +3.5 dBm or 2mW, rather than the 1 mW—0 dBm—that many single-chip 802.15.4 transmitters offer. This is the first time that Atmel has made such a device in monolithic form, although it has built similar functionality as an SiP (System-in-Package), twin-die product.

To match the needs of lowduty- cyclewireless-sensor-type applications, the chip has a deep-sleep-standby power demand of under 250 nA; it can wake from that state in under 70 µsec and be ready to receive after a further 350 µsec. The microcontroller is also energy- effi cient, Atmel says, running at 260 µA/MHz, which will yield 4.1 mA at 16 MHz; it will run at that frequency from 1.8V. The architecture includes hardware support for 128-bitkey encryption to keep the processing load on the MCU core to a minimum. The transceiver uses around 12.5 mA in receive and 14.5 mA in transmit mode. You can also run it with the receiver “listening” and the rest of the chip shut down, for a wake-on-radio confi guration.

The chip’s RF circuitry includes support for diversity; a pattern to establish the stronger of two signals from physically separated antennae is part of the preamble of each transmitted packet. The diversity system operates with or without external RF-signal-boost functions; the chip will control an external LNA (low-noise-amplifier) and PA (power amplifi er). One set of possible customers that would use a boosted confi guration, Atmel says, comprises those designing smart electricity meters. “They can use up to 0.25W of RF power— they are not concerned with lowest operating power,” Magnus Pedersen, Atmel’s product marketing director of MCU wireless solutions, commented.

Atmel designed the chip for Zigbee but has added modes that support data rates of up to 2 Mbit/sec; even low-rate video is possible, the company says, for designs such as door-entry security systems or baby monitors. Also generating design starts is the RF4CE wireless-consumerproduct standard; until now, most 802.15.4 remote-control designs have been proprietary, Atmel believes—but to accommodate increasing standardisation in the market, it will release a full RF4Ce stack “shortly”. Applicable to designs such as remote controls, the AVR MCU also has suffi cient processing capacity to run Atmel’s processorbased QTouch function library for capacitive touch control. The Atmega128RFA1 sells for $4.78 (10,000); a base development kit costs $79.

Atmel, www.atmel.com.