digital

There is a reason for high-frequency digital signals.

It is the Eccles-Jordan configuration of two amplifiers and feedback. Originally, they used vacuum tubes (it was about 1920).

Analog signal processing, using amplifiers and filters, generally takes in limited-bandwidth signals and outputs similarly limited-bandwidth signals. The Eccles-Jordan circuit and its developments are different, in that the output includes higher frequencies than the inputs (limited only by the physical makeup of the amplifiers used).

Flip-flops, Schmitt triggers, registers, latches, multivibrators, monostables, all are based on the Eccles-Jordan circuit. These are all bistable circuits (no matter what the input condition, only fullly ON or fully OFF output conditions will result), and are truly binary circuits as a result. The transition from ON to OFF occurs at full speed, and terminates only when the amplifiers saturate (i. e. limit out, lose gain due to limited power/voltage/current).

All modern digital logic technologies include these bistable elements, and that means that high frequency is always present in such digital logic (whether you need it or not).