Analog Devices AD640BD

Logarithmic Amplifier 1 Circuit - 20-CDIP

120 MHz, 50 dB Demodulating Logarithmic Amplifier

LOG OR ANTILOG AMPLIFIER, 1 FUNC

IC LOGARITHMIC 1 CIRCUIT 20CDIP

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 µA per dB). On chip resistors can be used to convert this output current to a voltage with several convenient slope options. A balanced signal output at +50 dB (referred to input) is provided to operate AD640s in cascade. The logarithmic response is absolutely calibrated to within ±l dB for dc or square wave inputs from ±0.75 mV to ±200 mV,with an intercept (logarithmic offset) at 1 mV dc. An integral X10 attenuator provides an alternative input range of ±7.5 mV to ±2 V dc. Scaling is also guaranteed for sinusoidal inputs. The AD640B is specified for the industrial temperature range of -40°C to +85°C and the AD640T, available processed to MIL-STD- 883B, for the military range of -55°C to +125°C. Both are available in 20-pin side brazed ceramic DIPs or leadless chip carriers (LCC). The AD640J is specified for the commercial temperature range of 0°C to +70°C, and is available in both 20-pin plastic DIP (N) and PLCC (P) packages. This device is now available to Standard Military Drawing (DESC) number 5962-9095501MRA and 5962-9095501M2A. An evaluation board is available for this product and may be ordered using the following product number: AD640-EB. Applications Radar, Sonar, Ultrasonic and Audio Systems Precision Instrumentation from DC to 120 MHz Power Measurement with Absolute Calibration Wide Range High Accuracy Signal Compression Alternative to Discrete and Hybrid IF Strips Replaces Several Discrete Log Amp ICs