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Cartesian loop transmitter IC: A point solution for linear RF

Winston-Salem, NC&#8212CML's new CMX998 Cartesian Feedback Loop Transmitter IC is designed to provide manufacturers of two-way wireless systems with a practical low-noise solution for linearizing the output of the system's RF power amplifier (PA). Indeed, it's the first fully integrated chip of its type, according to CML, suited for most of the non-constant envelope modulation systems used in today's wireless applications.

The CMX998 includes all the major functions required for a Cartesian system (i.e, using I and Q baseband inputs or coordinates, as opposed to polar) for the PA: Forward and feedback loops; local oscillator circuitry, including loop phase control; instability and error detectors, and uncommitted op-amps for input signal conditioning.

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The user needs add only a coupler and feedback attenuator. The CMX998's loop characteristics equip the chip for service over 100 MHz to 1 GHz, and channel bandwidths up to 150 kHz. In operation, the chip, sampling the output of the PA, works as a direct conversion quadrature mixer (with 30 dB linearization gain) to reproduce the modulating signal that's applied to its I and Q inputs, including PSK, QPSK, DQPSK, QAM, and ODFM. With the I and Q inputs indifferent to the modulation scheme per se, the chip can also be applied to analog FM. The CMX998 is thus suited for software defined radio (SDR) applications, TDMA-based systems, TETRA mobile station power classes up to 3W (Class-3), TETRA 2 terminals, APCO P25, aviation systems, and mobile satellite terminals.

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Click here for preview information (web registration is required for the full datasheet). The CMX998, in a 64-pin VQFN package with an added thermal ground pad to aid thermal performance, is priced at $10.90. An evaluation kit (EV9980) and support tools are also available to speed designs.

CML Microcircuits , 1-336-744-5050, www.cmlmicro.com

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