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VHF/UHF transmitter delivers up to 100Kbit/s

Posted: 10 Sep 2008 ?? ?Print Version ?Bookmark and Share

Keywords:power amplifier? VHF/UHF transmitter? frequency wide range?


Maxim Integrated Products has released the MAX7057 crystal-referenced, phased-locked loop (PLL) VHF/UHF transmitter for transmitting OOK/ASK/FSK data over a wide range of frequencies. The device can operate at any frequency in the 300MHz to 450MHz range with the proper crystal frequency, and it can transmit data at up to 100Kbit/s NRZ (50Kbit/sManchester coded).

To enable this flexibility, the MAX7057 integrates a programmable fractional-N PLL synthesizer with a wideband VCO. Additionally, it features internal capacitors that can be programmed to match the impedance of the power amplifier (PA) to the antenna. This topology ensures highly efficient transmission at multiple operating frequencies, making the MAX7057 well-suited for power-sensitive applications such as home security systems, remote controls, and garage door openers.

To further improve performance, the MAX7057 integrates an envelope-shaping resistor between the output of the PA and the power supply. This resistor slows the turn-on/off time of the PA in ASK mode, reducing the spectral width of the PA's modulated output signal.

In addition, the MAX7057's crystal-based architecture eliminates many of the common problems with SAW transmitters by providing greater modulation depth, faster frequency settling, tighter transmit-frequency tolerance, and reduced temperature dependence. The device thus provides better overall receiver performance when using a superheterodyne receiver with a narrow-IF (i.e., lower noise) bandwidth.

The MAX7057 operates from a single, 2.1V to 3.6V supply, and draws less than 1?A in standby mode and less than 8.4mA in transmit mode (50 percent duty cycle OOK). Available in a 16-pin SO package, the device is fully specified over the -40C to +125C automotive temperature range. Prices start at $1.55 (1,000-up, FOB USA).

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