Real-Time Analog Computational Unit (ACU)
The AD538 is a monolithic real-time computational circuit which provides precision analog multiplication, division, and exponentiation. The combination of low input and output offset voltages and excellent linearity results in accurate computation over an unusually wide input dynamic range. Laser wafer trimming makes multiplication and division with errors as low as 0.25% of reading possible, while typical output offsets of 100 microV or less add to the overall off-the-shelf performance level. Real-time analog signal processing is further enhanced by the device's 400 kHz bandwidth.
The AD538's overall transfer function is Vo=Vy(Vz/Vx)m. Programming a particular function is via pin strapping. No external components are required for one-quadrant (positive input) multiplication and division. Two-quadrant (bipolar numerator) division is possible with the use of external level shifting and scaling resistors. The desired scale factor for both multiplication and division can be set using the on-chip +2 V or +10 V references, or controlled externally to provide simultaneous multiplication and division. Exponentiation with an M value from 0.2 to 5 can be implemented with the addition of one or two external resistors.
Direct log ratio computation is possible by utilizing only the log ratio and output sections of the chip. Access to the multiple summing junctions adds further to the AD538's flexibility. Finally, a wide power-supply range of ±4.5 V to ±18 V allows operation from standard ±5 V, ± 12 V and ± 15 V supplies.
The AD538 is available in two accuracy grades (A and B) over the industrial (-25°C to +85°C) temperature range and one grade (S) over the military (-55°C to +125°C) temperature range. The device is packaged in an 18-pin TO-118 hermetic size-brazed ceramic DIP. A-grade chips are also available.
At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.