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RF control circuit optimises Airfast Doherty amplifiers

Posted: 30 May 2013 ?? ?Print Version ?Bookmark and Share

Keywords:Freescale? RF? control circuit? Airfast Doherty? amplifiers?

Freescale Semiconductor has recently introduced an advanced gallium arsenide (GaAs) monolithic microwave integrated circuit(MMIC) control circuit specifically designed to optimise the performance of the company's Airfast Doherty amplifiers.

The new MMDS20254H advanced Doherty alignment module (ADAM) enables more accurate alignment of phase and amplitude on the carrier and peaking paths of high-power Doherty amplifiers, thereby improving overall base station performance. The sophisticated technology also helps enhance power efficiency while boosting performance across the entire cellular frequency band.

The device is a GaAs MMIC based on E-pHEMT and InGaP HBT technology. Housed in a RoHS-compliant industry-standard 6 mm QFN package, the device allows phase and peaking adjustments from 1800 to 2200MHz.

Fuelled by the widespread adoption of TD-LTE and W-CDMA, Doherty amplifiers have regained prominence as an industry standard, providing high power-added efficiency when amplifying the types of signals associated with these popular protocols. Freescale's MMDS20254H ADAM device offers exceptional linearity/efficiency trade-offs, while improving output power. The solution includes a coupler, digitally selectable phase shifters and step attenuators, while operating from a single voltage supply. The MMDS20254H is suitable for transmit protocols such as W-CDMA and LTE, using frequencies from 1800 to 2200MHz, and is controlled using a SPI interface.

It has a constant 90 degree phase offset between port 2 and port 3 versus frequency (500MHz bandwidth). Digital adjustment is possible to optimise power amplifier performance under different conditions, including power level, supply voltage and temperature.

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