The AD641 is a 250 MHz, demodulating logarithmic amplifier with an accuracy of ±2.0 dB and 44 dB dynamic range. The AD641 uses a successive detection architecture to provide an output current that is logarithmically proportional to its input voltage. The output current can be converted to a voltage using one of several on-chip resistors to select the slope. A single AD641 provides up to 44 dB of dynamic range at speeds up to 250 MHz, and two cascaded AD641s together can provide 58 dB of dynamic range at speeds up to 250 MHz. The AD641 is fully stable and well characterized over either the industrial or military temperature ranges.

The AD641 is not a logarithmic building block, but rather a complete logarithmic solution for compressing and measuring dynamic range signals. The AD641 is comprised of five stages and each stage has a full wave rectifier, whose current pends on the absolute value of its input voltage. The output of these stages are summed together to provide the demodulated output current scaled at 1 mA per decade (50 µA/dB).

Without utilizing the 10x input attenuator, log conformance of 2.0 dB is maintained over the input range -44 dBm to 0 dBm. The attenuator offers the most flexibility without significantly impacting performance.

The 250 MHz bandwidth and temperature stability make this product ideal for high speed signal power measurement in RF/IF systems. ECM/Radar and Communication applications are routinely in the 100 MHz-180 MHz range for power measurement. The bandwidth and accuracy, as well as dynamic range, make this part ideal for high speed, wide dynamic range signals.

The AD641 is offered in industrial (-40°C to +85°C) and military (-55°C to +125°C) package temperature ranges. Industrial versions are available in plastic DIP and PLCC; MIL versions are packaged in cerdip.

An evaluation board is available for this product and may be ordered using the following product number: AD641-EB.