ISM-band transmitters

25 May 2011 Telecoms, Datacoms, Wireless, IoT

Semtech has launched a new ‘power-and-go’ radio frequency (RF) platform designed to replace IR (infrared) and RF discrete designs with an integrated, cost-effective radio solution for one-way remote keyless entry (RKE) and remote control products in consumer, home/building automation, as well as active RFID applications, such as shipment and asset tracking systems, patient monitoring systems and social alarms.

The new SX1240 and SX1242 ISM-band RF transmitters require only an external crystal and antenna impedance matching network. They simplify design by integrating ‘power-and-go’ modes which are preset for 434 MHz and 868 MHz (SX1240) or 345 MHz (SX1242), eliminating the need for a microcontroller. They can also be used with a wide variety of low-cost antenna technologies that do not require active antenna re-tuning. The SX1240 and SX1242 can be paired with Semtech’s low-power SX1239 RF receiver for a complete radio solution.

The SX1240 transmitter operates in the 418, 434 and 868 MHz, licence-free ISM bands and works with FSK and OOK modulation formats up to 100 Kbps. For design flexibility, it offers two application modes. In power-and-go mode, it can be pre-configured as either a 434 MHz OOK transmitter or an 868 MHz FSK transmitter, without the need for an MCU, by simply setting the control pin. In advanced mode, it can be used with an MCU and programmed via a two-wire interface for designs requiring custom configuration of output power, modulation format, operating channel and other communication parameters.

The SX1240 extends battery life with 16,5 mA current consumption, which is configurable at +10 dBm output power or 9 mA current consumption at 0 dBm output power, combined with a 500 nA sleep mode current. Its low current consumption makes it suitable for coin-cell batteries, which are current limited at 20 mA. The SX1240 combined with SX1239 RF receiver features a high link budget of 130 dBm, allowing use of a very small antenna to further reduce the total design footprint.

The SX1242 transmitter offers similar features to the SX1240, but operates in the 345 MHz ISM band and works with OOK modulation formats up to 10 Kbps. It also offers both power-and-go mode (preconfigured to operate without a microcontroller at 345 MHz) and advanced mode. It provides 22 mA current consumption configurable at +12 dBm output power, 500 nA sleep mode current, and a link budget of 132 dBm when combined with SX1239 RF receiver.

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