Power Detector
Fürstenfeldbruck, Germany: According to National Semiconductor, its new linear root-mean-square (RMS) radio-frequency (RF) power detector provides high precision with up to 40dB dynamic range. The PowerWise LMH2120 increases wireless coverage and extends battery life for 3G and 4G mobile handsets, claims the company.
The LMH2120 enables accurate RF power-amplifier (PA) measurements, which are used to control transmit power and avoid interference with neighbouring signals. It provides stable performance over the full temperature range of -40°C to 85°C, with a temperature variation of just ±0.5dB over a wide 40dB dynamic range at 1900MHz, minimising guard bands. NSC says this feature extends coverage and quality of service, such as higher uplink data rates at greater distance from the cell tower.
Performance remains consistent across various modulation schemes in multimode handsets and data cards using CDMA, W-CDMA, UMTS, LTE, GSM, and GPRS cellular standards. It provides modulation-independent measurements of less than 0.3dB, which eliminates the extensive lookup tables required for accuracy. A shutdown pin reduces power consumption in between measurements to extend handset battery life.
The power detector operates from a single 2.7V to 5V supply and provides an output voltage proportional to the RF input power in dBm. This minimises the need for extra calibration and reduces the resolution requirement for the system’s analog-to-digital converter. Handset designers can connect the device to the output of the PA with a directional coupler or a resistive tap.
Supply current runs at 2.9mA, and a low-power shutdown-mode reduces power consumption to 3.8µA. Frequencies of 50 MHz to 6GHz are supported, with an RF power detection range of -35 dBm to 5 dBm.
The LMH2120 joins the recently released LMH2110 LOG RMS RF power detector. The 2110 provides precise control of RF PAs operating from 50 MHz to 8 GHz, with an RF power detection range of -40 dBm to 5 dBm.
Available now, the LMH2120 comes in a small 0.82mm-by-1.22mm, 6-bump microSMD package. It costs $2.40 each in 1000-unit quantities.