GENERAL DESCRIPTION:

The AD8317 is a demodulating logarithmic amplifier, capableof accurately converting an RF input signal to a correspondingdecibel-scaled output. It employs the progressive compressiontechnique over a cascaded amplifier chain, each stage of whichis equipped with a detector cell. The device can be used in eithermeasurement or controller modes. The AD8317 maintainsaccurate log conformance for signals of 1 MHz to 8 GHz andprovides useful operation to 10 GHz. The input dynamic rangeis typically 55 dB (referenced to 50 Ω) with less than ±3 dBerror. The AD8317 has 6 ns/10 ns response time (fall time/risetime) that enables RF burst detection to a pulse rate of beyond50 MHz. The device provides unprecedented logarithmic interceptstability vs. ambient temperature conditions. A supply of 3.0 Vto 5.5 V is required to power the device. Current consumption istypically 22 mA, and it decreases to 200 μA when the device isdisabled. The AD8317 can be configured to provide a control voltage to apower amplifier or a measurement output from the VOUT pin.Because the output can be used for controller applications, specialattention has been paid to minimize wideband noise. In thismode, the setpoint control voltage is applied to the VSET pin. 

The feedback loop through an RF amplifier is closed via VOUT,the output of which regulates the output of the amplifier to amagnitude corresponding to VSET. The AD8317 provides 0 V to(VPOS − 0.1 V) output capability at the VOUT pin, suitable forcontroller applications. As a measurement device, VOUT isexternally connected to VSET to produce an output voltage,VOUT, that is a decreasing linear-in-dB function of the RF inputsignal amplitude.The logarithmic slope is 22 mV/dB, determined by the VSETinterface. The intercept is 15 dBm (referenced to 50 Ω, CWinput) using the INHI input. These parameters are very stableagainst supply and temperature variations.The AD8317 is fabricated on a SiGe bipolar IC process and isavailable in a 2 mm × 3 mm, 8-lead LFCSP with an operatingtemperature range of −40°C to +85°C. 

FEATURES:

Wide bandwidth: 1 MHz to 10 GHz

High accuracy: ±1.0 dB over temperature

55 dB dynamic range up to 8 GHz ± 3 dB error

Stability over temperature: ±0.5 dB

Low noise measurement/controller output, VOUT

Pulse response time: 6 ns/10 ns (fall/rise)

Small footprint, 2 mm × 3 mm LFCSP

Supply operation: 3.0 V to 5.5 V at 22 mA

Fabricated using high speed SiGe process

APPLICATIONS:

RF transmitter PA setpoint control and level monitoring

Power monitoring in radio link transmitters

RSSI measurement in base stations, WLANs, WiMAX, and radars