Crystal-Based Transmitter Extends Range Of Wirless Gadgets

Short-range wireless applications like remote keyless entry fobs, garage door openers, security products, and remote sensors can improve the accuracy of their frequency settings thanks to the MAX7044 VHF/UHF IC transmitter.

With the help of a crystal-based phase-locked loop (PLL), this device from Maxim Integrated Products eliminates the transmitter frequency problems often encountered with LC or surface-acoustic-wave-based frequency-selection approaches used with competing products. Its inherent frequency stability enables Maxim to use a narrower IF bandwidth, 50 kHz instead of the usual 600 kHz, improving sensitivity by 9 dB. The PLL uses a low-cost 10- to 15-MHz surface-mount crystal. Settling time of the PLL for frequency changes is 250 µs. Total frequency setting range is 300 to 450 MHz.

The MAX7044 also employs amplitude shift keying (ASK). Maximum output power is +13 dBm. Power is actually adjustable with an external resistor from −10 to +13 dBm into a 50-(omega) load. Line coding is typically Manchester. Data rates up to 100 kbits/s can be achieved. The chip can operate from a lithium-ion cell with a voltage as low as 2.1 V. Standby current is only 100 µA. Current draw at 0-dBm output power is 3.7 mA.

Housed in a 3- by 3-mm eight-pin SOT23 package, the MAX7044 costs $1.17 in 10,000-unit quantities. An evaluation kit is available to facilitate design.