RF power detector stays accurate over temperature

April 26, 2007
The LMV221 RF power detector from National Semiconductor Corp., Santa Clara, Calif., targets mobile-phone power controls in current and emerging cellular standards, including GSM, CDMA, UMTS and TD-SCDMA.

RF power detector stays accurate over temperature

The detector gives precise, stable, and accurate control of power over a wide dynamic and temperature range. The LMV221 handles multiband frequencies from 50 MHz to 3.5 GHz with 40 dB of dynamic range, giving stable performance from –40 to 85°C with ±0.5-dB accuracy.

Real-time transmitter power adjustments simplify system calibration and cut accuracy requirements for connected power amplifiers and variable-gain amplifiers. The LMV221operates from a single 2.7 to 3.3-Vdc supply and gives an output voltage proportional to RF input power in dBm (power measurement relative to 1 mW). Output voltage goes from 0.3 to 2 Vdc and can scale to meet the input range of various analog-to-digital converters. The LMV221 detects RF power from –45 to –5 dBm and is well suited for direct use with a 30-dB directional coupler. The device remains in low-power shutdown mode until powered up through an enable pin.

The LMV22x RF power detectors extend the company's family of RF log-amp and mean-square detectors. They provide RF power data to its LM320x dc/dc converters, including the LM3208. The LM3208 dynamically controls supply voltage of WCDMA and CDMA RF power amplifiers to boost overall system efficiency. This combination of dc-dc converter plus power detector generates real-time optimum power supply voltage for a given RF transmit power, yielding significant efficiency gains throughout the entire transmit range, especially at low transmit power levels. The result: Longer battery life in portable RF applications.

National Semiconductor Corp.,

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