AD640TE/883B

The AD640 is a complete monolithic logarithmic amplifier. A single
AD640 provides up to 50 dB of dynamic range for frequencies
from dc to 120 MHz. Two AD640s in cascade can provide up to
95 dB of dynamic range at reduced bandwidth. The AD640 uses a
successive detection scheme to provide an output current proportional to the logarithm of the input voltage. It is laser calibrated to
close tolerances and maintains high accuracy over the full military
temperature range using supply voltages from ?4.5 V to ?7.5 V.
The AD640 comprises five cascaded dc-coupled amplifier/limiter
stages, each having a small signal voltage gain of 10 dB and a ?3 dB
bandwidth of 350 MHz. Each stage has an associated full-wave
detector, whose output current depends on the absolute value of its
input voltage. The five outputs are summed to provide the video
output (when low-pass filtered) scaled at 1 mA per decade (50 ?A
per dB). On chip resistors can be used to convert this output current to a voltage with several convenient slope options.