Ken Shirriff's blog
Reverse-engineering an early calculator chip with four-phase logic
In 1969, high-density MOS integrated circuits were still new and logic circuits were constructed in a variety of ways.
One technique was "four-phase logic",
which provided ten times the speed and density of standard logic gates while using 1/10 the power.1
One notable application of four-phase logic was calculators.
In 1969, Sharp introduced the first calculator built from high-density MOS chips, the
QT-8D, followed by
the world's smallest calculator, the handheld EL-8.
These calculators were high-end products, selling for $345 (about $1800 today).
The Sharp EL-8 calculator. Note the unusual 8-segment display for the digits. Photo by Felix Maschek, CC BY-SA 3.0 DE.