RF power detectors offer accuracy, stability and ultra-small packaging
National Semiconductor Corporation's newest family of RF power detectors is tailored for wireless applications that require high frequency and range. Linearity-in-dB, stability, reliability and accuracy are important criteria for RF applications. This family includes the smallest RF logarithmic (log) amp and mean-square detectors that meet these criteria. These devices give RF designers outstanding RF system performance, high reliability, ease of use and the flexibility to meet worldwide standards for communications certification.
National's LMV225, LMV226 and LMV228 are log-amp RF power detectors with multiband frequency ranges from 450 MHz to 2 GHz. These devices provide an accurate temperature and supply-compensated output voltage that relates linearly to the RF input power in dBm. These devices operate with a single supply from 2.7 V to 5.5 V.
The LMV225 has an RF power detection range from -30 dBm to 0 dBm and is ideally suited for direct use in combination with resistive taps, eliminating the need for a directional coupler. If preferred, the LMV225 can also be used with a 30 dB to 35dB directional coupler. The LMV226 and LMV228 have a detection range from -15 dBm to 15 dBm and are intended for use in combination with a 20 dB directional coupler. The LMV225 and LMV228 are targeted for the CDMA and WCDMA applications, while the LMV226 is equipped with a buffered output, which makes it suitable for GSM, EDGE, GPRS and TDMA applications. These devices remain in a low-power-consumption shutdown mode until powered up through the enable pin to drive the lowest power consumption possible. The output voltage ranges from 0.2 V to 2 V and can be scaled down to meet analog-to-digital converter input range requirements.
The LMV225 and LMV228 RF power detectors work in cooperation with the supplier's LM320x series of supervisory power amplifiers (SuPA), allowing an adaptive PA supply control. The power detectors are used to control/drive the SuPA to achieve better power efficiency and accurate transmit power control. The SuPA generates the required supply voltage (Vout) of the power amplifier for a given output transmit power. This combination of SuPA 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.
Additionally, the LMV232 is a mean-square RF detector with two RF inputs optimized to work with 20 dB directional couplers and without any external components, providing the smallest footprint for mobile RF designs. The LMV232 true mean-square power detection allows the detector's response to be independent of the RF waveshape, resulting in less calibration steps for complex (WCDMA /CDMA) RF input signals and providing excellent temperature stability. The dual-input structure allows the power control in dual-mode phones to be handled by a signal detector, or it can be used to detect a mismatched antenna condition.
The LMV232's architecture eliminates the need for phone manufacturers to perform factory trimming, which reduces system certification time and speeds their time to market. It has two digital input pins, enabling a low-power shutdown mode and the selection between the two RF inputs. The external gain and filter bandwidth can be set with an external resistor and capacitor for optimal dynamic range and ripple suppression. The LMV232 enables customers to improve performance, shorten design cycles and speed certifications.
For more information, visit www.national.com
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