Very nice article! The technique of using an op amp with capacitor as an integrator is also a key component of analog computers. By hooking up a few integrators, an analog computer can quickly solve differential equations (in the 1960s, much faster than a digital computer could).
This is also why op-amps are named that - Operational Amplifiers, they can do many mathematical operations.
My college electronics prof was old-school enough who told us back in his day it was “standard practice” to use pp-amps to solve differential equations from their Calc class.
Prior to moving to PDP-11's and paper-tape, the special-effects company I worked for many years ago used analogue computers stuffed with op-amps to control the motion of camera rigs - i.e. analogue motion control. I never saw one in operation, but apparently a cardinal sin was opening the door when the system was in operation (the temperature change would cause enough error to ruin the shot).
This is the best article on DCO that I ever seen, so many thanks to the author. Often digital oscillators are unfairly misrepresented and it's difficult to find a fair comparison on the fundamentals of it.
