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
wide dynamic range signals. The AD641 is comprised of five
stages and each stage has a full wave rectifier, whose current
depends 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 10× 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.
Applications
- IF/RF signal processing
- Received Signal Strength Indicator (RSSI)
- High speed signal compression
- High speed spectrum analyzer
- ECM/radar
