The 8579 and it’s related product family provides a simple one-chip method of driving 2-input (series/shunt) GaAs MMIC attenuators with a binary coded word. The 8579 is capable of 8-bit monotonic resolution, and linearizing resistors can be calculated with freely-provided software.
The Impellimax model 8579 size is a 22 lead chip, .625 by .375 by .115 nominal dimensions. It accepts an 8-bit binary word and provides two voltage outputs which can drive a GaAs MMIC attenuator in a linear mode, resulting in 256 linearly-spaced attenuation steps. The output transfer function curves are user-adjustable, by means of four breakpoint connections, to allow tailoring to specific GaAs IC’s and attenuation ranges.
The unit operates with supplies in the range of +/-5V to +/-15V, with TTL compatibility assured over this full range. There are internal .01 uF power supply decoupling caps on both supplies. Power supply consumption is typically under 20 mA per supply, depending on the application circuit.
Settling time for a half-band step is typically in the range of 50 to 200 nsec.