Crystal-based ASK transmitter

Maxim has introduced the MAX7044, claimed to be the world's smallest VHF/UHF, PLL-based, ASK transmitter with +13 dBm output power packaged in a 3 x 3 mm, 8 pin SOT23.

The transmitter is suitable for low-cost, high-volume applications. Examples include key-fobs, security products, garage door openers, and remote sensors operating in the 300 to 450 MHz range.

The device uses a simple, single-input data interface and a clock-out feature to eliminate the need for an MCU resonator. The device operates from a single lithium-ion (Li+) cell down to 2. 1 V and consumes 100 µA in standby mode.

Using an external resistor, the output power can be adjusted from -10 dBm to +13 dBm into a 50 ohm load.

At +13 dBm, the device consumes 8.6 µA at 315 MHz, when using a 50% duty-cycle encoding scheme such as Manchester.

Current consumption is 3.7 mA at 0 dBm output, and the device can transmit at data rates up to 100 Kbps.

Once enabled, the 7044 takes 250 ms for the PLL and crystal to settle and be available for transmission. The device accepts crystal frequencies between 10 and 15 MHz. The device's crystal-based PLL eliminates most LC- or SAW-based transmitter problems. The inherent accuracy of the crystal frequency facilitates a narrower IF-bandwidth in the receiver to improve system sensitivity.

A sensitivity improvement of 9 dB is possible by narrowing the IF bandwidth from 600 to 50 kHz when the device is used in conjunction with receivers such as the MAX1470, MAX1473 or MAX7033.