Analog Devices Inc.United States

The AD8317 is a demodulating logarithmic amplifier, capable of accurately converting an RF input signal to a corresponding decibel-scaled output. It employs the progressive compression technique over a cascaded amplifier chain, each stage of which is equipped with a detector cell. The device can be used in either measurement or controller modes. The AD8317 maintains accurate log conformance for signals of 1 MHz to 8 GHz and provides useful operation to 10 GHz. The input dynamic range is typically 55 dB (referenced to 50 Ω) with less than ±3 dB error. The AD8317 has 6 ns/10 ns response time (fall time/rise time) that enables RF burst detection to a pulse rate of beyond 50 MHz. The device provides unprecedented logarithmic intercept stability vs. ambient temperature conditions. A supply of 3.0 V to 5.5 V is required to power the device. Current consumption is typically 22 mA, and it decreases to 200 μA when the device is disabled. The AD8317 can be configured to provide a control voltage to a power amplifier or a measurement output from the V OUT pin. Because the output can be used for controller applications, special attention has been paid to minimize wideband noise. In this mode, the setpoint control voltage is applied to the V SET pin. The feedback loop through an RF amplifier is closed via V OUT , the output of which regulates the output of the amplifier to a magnitude corresponding to V SET . The AD8317 provides 0 V to (V POS − 0.1 V) output capability at the V OUT pin, suitable for controller applications. As a measurement device, V OUT is externally connected to V SET to produce an output voltage, V OUT , that is a decreasing linear-in-dB function of the RF input signal amplitude. The logarithmic slope is –22 mV/dB, determined by the V SET interface. The intercept is 15 dBm (referenced to 50 Ω, CW input) using the INHI input. These parameters are very stable against supply and temperature variations. The AD8317 is fabricated on a SiGe bipolar IC process and is available in a 2 mm × 3 mm, 8-lead LFCSP with an operating temperature range of –40°C to +85°C. Applications RF transmitter PA setpoint control and level monitoring Power monitoring in radio link transmitters RSSI measurement in base stations, WLANs, WiMAX, and radars