US : National Semiconductor introduced the industry’s first radio frequency (RF) power detector with guaranteed accuracy over temperature and RF production testing for third-generation (3G) mobile phone power controls.
National’s LMV221 RF power detector enables precise power control that is stable over a large temperature range and accurate over a wide dynamic range. It provides multi-band frequency ranges from 50 MHz to 3.5 GHz with 40 dB of dynamic range, as well as stable performance over the full temperature range of minus 40 degrees C to 85 degrees C with plus or minus 0.5 dB accuracy. Its real-time transmitter power adjustments simplify system calibration and reduce accuracy requirements for power amplifiers and variable gain amplifiers. The LMV221 is designed for current and emerging cellular standards, including GSM, CDMA, UMTS and TD-SCDMA.
Operating with a single supply from 2.7V to 3.3V, the LMV221 provides an output voltage that is proportional to the RF input power in dBm. This decreases the designer’s need for extra calibration as well as reducing the resolution needed in the system’s analog-to-digital converter. The output voltage ranges from 0.3V to 2V and can be scaled down to meet analog-to-digital converter input range requirements.
The LMV221 has an RF power detection range from -45 dBm to -5 dBm and is well-suited for direct use with a 30 dB directional coupler. This device remains in a low-power-consumption shutdown mode until powered up through the enable pin to drive the lowest power consumption possible.
This new chip extends National’s family of RF log amp and mean-square detectors that were introduced in July 2005. The LMV225, LMV226 and LMV228 are RF power detectors with multi-band frequency ranges from 450 MHz to 2 GHz. National’s LMV232 is an RF detector with two RF inputs optimized to work with 20 dB directional couplers.
The LMV22x family of RF power detectors provides RF power data to National’s family of LM320x DC/DC converters, including the LM3208. The LM3208 dynamically controls the supply voltage of WCDMA and CDMA RF power amplifiers to improve the overall system efficiency. This combination of DC/DC converter plus power detector generates the real-time optimum power supply voltage (Vout) for a given RF transmit power, yielding significant efficiency improvements throughout the entire transmit range, especially at low transmit power levels. The result is longer battery life in portable RF applications.