Most of today's sophisticated wireless technologies require some form of precise power monitoring or control for proper operation. RF power detection with a diode still works fine at the lower frequencies, but the microwave region craves more advanced techniques. Some ICs are available for this application, but the AD8318 offers another option that could substantially improve the process.
Developed by Analog Devices, the AD8318 is a successor to the well-known AD8313 power detector. This logarithmic amplifier operates from 1 to 8 GHz. The multistage amplifier has an overall input range of −60 to 0 dBm at 50-Ω impedance. Dynamic range is 55 dB ±1 dB up to 5.8 GHz. Each stage of amplification has its own full-wave rectifier power detector. All detector outputs are summed at the input to an op amp that provides a voltage output linear in dB. Maximum output drive current is 60 mA. Its circuitry is temperature-compensated from −40°C to 85°C and is stable to ±0.5 dB.
Another key feature is an on-chip temperature sensor that provides an output of 2 mV/°C. Pulse response time is a speedy 8 ns, making it useful in radar applications. A separate voltage-to-current conversion amplifier permits feedback detection, enabling the AD8318 to be used in closed-loop control applications.
Cellular infrastructure transceivers and power amplifiers, especially in GSM, CDMA, and W-CDMA basestations, are among the applications suited for the device. Others include 802.11a/b/g wireless local-area network (WLAN) systems and the new fixed-broadband wireless access equipment based on 802.16, 802.20, and WiMAX standards.
The AD8318 is made with 0.35-µm bipolar silicon germanium. It operates from 5 V dc with a maximum current drain of 65 mA. Housed in a 16-lead LFCSP package, the power detector costs $5.99 in 1000-unit quantities. Samples are available now as an evaluation board. Production quantities are slated for July.
Analog Devices Inc.