Datasheet AD641 (Analog Devices)

a
250 MHz Demodulating Logarithmic Amplifier AD641 FEATURES PIN CONFIGURATIONS Logarithmic Amplifier Performance 20-Lead Plastic DIP (N) Usable to 250 MHz 20-Lead Cerdip (Q) 44 dB Dynamic Range
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2.0 dB Log Conformance –INPUT 1 20 +INPUT 37.5 mV/dB Voltage Output Stable Slope and Intercepts ATN LO 2 19 ATN OUT 2.0 nV/
√
Hz Input Noise Voltage ATN COM 3 18 CKT COM 50
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V Input Offset Voltage ATN COM 4 17 RG1 Low Power ATN IN 5 16 AD641 RG0
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5 V Supply Operation TOP VIEW BL1 6 15 RG2 (Not to Scale) 9 mA (+VS), 35 mA (–VS) Quiescent Current –V 7 14 S LOG OUT Onboard Resistors ITC 8 13 LOG COM Onboard 10
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Attenuator BL2 9 12 +VS Dual Polarity Current Outputs –OUTPUT 10 11 +OUTPUT Direct Coupled Differential Signal Path APPLICATIONS 20-Lead PLCC (P) IF/RF Signal Processing Received Signal Strength Indicator (RSSI) High Speed Signal Compression High Speed Spectrum Analyzer ATN COM ATN LO –INPUT +INPUT ATN OUT ECM/Radar 3 2 1 20 19 ATN COM 4 PIN 1 18 CKT COM IDENTIFIER PRODUCT DESCRIPTION ATN IN 5 17 RG1 AD641
The AD641 is a 250 MHz, demodulating logarithmic amplifier
BL1 6 16 RG0 TOP VIEW
with an accuracy of ± 2.0 dB and 44 dB dynamic range. The
–V 7 (Not to Scale) 15 S RG2
AD641 uses a successive detection architecture to provide an
ITC 8 14 LOG OUT
output current that is logarithmically proportional to its input
9 10 11 12 13
voltage. The output current can be converted to a voltage using
S
one of several on-chip resistors to select the slope. A single
BL2 +V
AD641 provides up to 44 dB of dynamic range at speeds up to
SIG –OUT SIG +OUT LOG COM
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 The 250 MHz bandwidth and temperature stability make this military temperature ranges. product ideal for high speed signal power measurement in RF/ The AD641 is not a logarithmic building block, but rather a IF systems. ECM/Radar and Communication applications are complete logarithmic solution for compressing and measuring routinely in the 100 MHz–180 MHz range for power measure- wide dynamic range signals. The AD641 is comprised of five ment. The bandwidth and accuracy, as well as dynamic range, stages and each stage has a full wave rectifier, whose current make this part ideal for high speed, wide dynamic range signals. depends on the absolute value of its input voltage. The output The AD641 is offered in industrial (–40°C to +85°C) and mili- of these stages are summed together to provide the demodulated tary (–55°C to +125°C) package temperature ranges. Industrial output current scaled at 1 mA per decade (50 µA/dB). versions are available in plastic DIP and PLCC; MIL versions Without utilizing the 10× input attenuator, log conformance of are packaged in cerdip. 2.0 dB is maintained over the input range –44 dBm to 0 dBm. The attenuator offers the most flexibility without significantly impacting performance. REV. D 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
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Document Outline FEATURES PRODUCT DESCRIPTION PIN CONFIGURATIONS AD641--SPECIFICATIONS ELECTRICAL CHARACTERISTICS THERMAL CHARACTERISTICS ABSOLUTE MAXIMUM RATINGS ESD CAUTION REVISION HISTORY AD641--TYPICAL DC PERFORMANCE CHARACTERISTICS TYPICAL AC PERFORMANCE CHARACTERISTICS CIRCUIT DESCRIPTION CIRCUIT OPERATION FUNDAMENTALS OF LOGARITHMIC CONVERSION INTERCEPT STABILIZATION CONVERSION RANGE EFFECT OF WAVEFORM ON INTERCEPT LOGARITHMIC CONFORMANCE AND WAVEFORM SIGNAL MAGNITUDE INTERCEPT AND LOGARITHMIC OFFSET OPERATION OF A SINGLE AD641 ACTIVE CURENT-TO-VOLTAGE CONVERSION EFFECT OF FREQUENCY ON CALIBRATION SOURCE RESISTANCE AND INPUT OFFSET USING HIGHER SUPPLY VOLTAGES USING THE ATTENUATOR OPERATION OF CASCADED AD641s ELIMINATING THE EFFECT OF FIRST STAGE OFFSET PRACTICAL APPLICATIONS RSSI APPLICATIONS 250 MHz RSSI CONVERTER WITH 58 dB DYNAMIC RANGE OUTLINE DIMENSIONS ORDERING GUIDE