20-Lead Plastic DIP (N) 20-Lead Cerdip (Q) –INPUT 1
ATN LO 2
19 ATN OUT
ATN COM 3
18 CKT COM
ATN COM 4 ATN IN 5
TOP VIEW 15 RG2 (Not to Scale) 14 LOG OUT –VS 7 ITC 8
13 LOG COM
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.
PIN 1 IDENTIFIER
6 7 8
18 CKT COM 17 RG1
TOP VIEW (Not to Scale)
15 RG2 14 LOG OUT
10 11 12 13
ATN COM 3
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).
20-Lead PLCC (P)
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.
APPLICATIONS IF/RF Signal Processing Received Signal Strength Indicator (RSSI) High Speed Signal Compression High Speed Spectrum Analyzer ECM/Radar
FEATURES Logarithmic Amplifier Performance Usable to 250 MHz 44 dB Dynamic Range ±2.0 dB Log Conformance 37.5 mV/dB Voltage Output Stable Slope and Intercepts 2.0 nV/√Hz Input Noise Voltage 50 µV Input Offset Voltage Low Power ±5 V Supply Operation 9 mA (+VS), 35 mA (–VS) Quiescent Current Onboard Resistors Onboard 10X Attenuator Dual Polarity Current Outputs Direct Coupled Differential Signal Path
250 MHz Demodulating Logarithmic Amplifier AD641
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.
REV. A Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
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