Closed loop control cuts cellphone power amp drain

Edited by the Electronicstalk editorial team Feb 14, 2003

Leveraging its expertise in RF detector ICs for mobile handsets, Analog Devices has entered the cellular handset power amplifier market with the X-PA family of RF power amplifier modules.

Leveraging its expertise in RF detector ICs for mobile handsets, Analog Devices has entered the cellular handset power amplifier market with the introduction of its new X-PA family of RF power amplifier modules.

Rounding out ADI's offerings for the GSM cellphone signal chain, the new PA modules integrate the company's industry leading RF detection and power control technology enabling cellphone manufacturers to achieve longer battery life, improve performance and lower manufacturing costs.

"Analog Devices' X-PA power amplifier presents cellphone designers with the best solution on the market", said Robbie McAdam, Vice President, Analog Semiconductor Components Division, Analog Devices.

"ADI's unique closed-loop power control technique offers a vast improvement over both discrete diode circuit solutions and solutions using open-loop voltage and current sensing methods".

ADI's first product in its new X-PA family of PA modules is the ADL5551.

It is the cellular industry's first power amplifier module with integrated control using closed-loop output power measurement.

The new module also employs state-of-the-art gallium arsenide (GaAs) hetero-junction bipolar (HBT) power amplifier process technology.

The innovative architecture results in battery power savings of more than 20%, as compared with competitors' open-loop voltage and current sensing approaches.

Subsequent new products will provide similar benefits to all major cellular standards, offering reduced size and higher integration.

Closed-loop output power control remains the dominant control approach in the cell phone industry.

Output power control is superior to voltage or current control, as it directly measures actual output power instead of indirectly controlling it by measuring supply voltage and current.

It is the most accurate method in poor VSWR (varying load) situations, leading to better specific absorption ratio (SAR) ratings and improved handset performance.

Voltage and current control are inherently inferior in efficiency at lower output levels.

The ADL5551 reduces time to market and lowers manufacturing costs, requiring only one calibration point in each band.

In addition only one ramping profile is required for all power levels to meet GSM mask specifications, unlike voltage and current sense methods, which demand multiple ramp profiles.

The ADL5551 complements ADI's Othello GSM RFIC product family and is quad-band GSM (850, 900, 1800, 1900MHz) and GPRS-compliant to level 12.

It operates with a 2.9 to 4.5V power supply and is available in a 10 x 10 x 1.4mm LCC package.

Pricing for the ADL5551 starts at $5 per unit in 10,000-piece quantities.

The device is in full production now.