The AD640 is a complete monolithic logarithmic amplifier. A single AD640 provides dynamic range of up to 50 dB, with frequencies ranging from dc to 120 MHz. Two ad640 cascades can provide dynamic range of up to 95 dB with reduced bandwidth. The AD640 uses a continuous detection scheme to provide output current proportional to the logarithm of the input voltage. It is calibrated with a laser to close tolerances and maintains high accuracy across the military temperature range using a supply voltage of ± 4.5V to ± 7.5V.
Functional block diagram
The AD640 consists of five cascaded DC coupled amplifier/limiter stages, each with 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 add up to provide video output (when low-pass filtering), scaled at 1 mA (50 μA/dB) per decade.
The on-chip resistor can be used to convert this output current to voltage with several handy slope options. Provides +50 dB balance signal output (reference input) for cascading operation of the ad640. The logarithmic response is calibrated absolutely to ±1 dB, and the dc or square wave input ranges from ±0.75 mV to ±200 mV, with an intercept (logarithmic offset) at 1 mV dc. The integrated X10 attenuator provides an optional input range from ± 7.5mV to ±2v dc. Scaling also guarantees sinusoidal input.
The AD640B is suitable for the industrial temperature range from -40°C to +85°C, and the AD640T can be processed in MILSTD-883B for the military temperature range from -55°C to +125°C. Both devices are available in 20-lead-side brazed ceramic dip or lead-free chip carrier (LCC). The AD640J is available in a commercial temperature range of 0°C to +70°C and is offered in 20-lead plastic DIP (N) and PLCC (P) packages. The equipment is now available for use with standard Military drawing (DESC) numbers 5962-9095501MRA and 5962-9095501M2A.