Maxim Integrated Products' MAX1479 is a miniature VHF/UHF PLL-based ASK/FSK transmitter that delivers more than +10dBm output.

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Housed in a small, 3 mm x 3 mm, 16-pin thin QFN package, this 300 MHz to 450 MHz low-power crystal-based ASK/FSK transmitter is designed for low-cost, high-volume applications where space is critical, such as tire pressure monitoring systems (TPMS), key fobs, security products, garage door openers, and remote sensors operating in the 300 MHz to 450 MHz band. The MAX1479 has a simple data interface and a divider-programmable clock-out feature that eliminates the need for an MCU resonator. It can run directly off a lithium cell, and will operate down to 2.1V, consuming only 0.2 nA of current in standby mode.

The output power of the MAX1479 can be adjusted from -10 dBm to +10 dBm into a 50 Ohm load by using an external resistor. At the +10dBm power level, the MAX1479 consumes 6.7 mA of current at 315 MHz when using a 50% duty-cycle encoding scheme, such as Manchester. Current consumption is only 4.5 mA at 0 dBm output. The part can transmit at date rates up to 100 kbps in ASK and 20 kbps in FSK (both Manchester encoded).

Once the enable pin of the MAX1479 is activated, it takes only 200 microseconds for the PLL and crystal to settle and be available to transmit. As the device is targeted at small, portable applications, the MAX1479 accepts crystal frequencies from 9 MHz to 15 MHz, widely available in inexpensive, surface-mount packages. Because the MAX1479 uses a crystal-based PLL, most of the problems of an LC or SAW-based transmitter are eliminated. The inherent accuracy of the crystal frequency allows a narrower IF bandwidth in the receiver to improve system sensitivity. Used with a receiver like Maxim's MAX1470, MAX1471, or MAX1473, the MAX1479 transmitter can improve overall system sensitivity 9 dB simply by narrowing the IF bandwidth from 600 kHz to 50 kHz. Improved sensitivity translates directly to greater range or more reliable transmissions.

The MAX1479 operates over the automotive temperature range (-40°C to +125°C). Prices start at $0.99, in quantities of 10,000 pieces and up. Evaluation kits are available to speed designs.