RF power detector stays accurate over temperature
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.
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National Semiconductor Corp.,
national.com/pf/LM/LMV221.html