was thinking of the possibility of ussing differentiators to design circuits according to a differential equation.
The cap-r-gnd forms a highpass whose output is rougly the derivative of the input, in the taylor sense.
The opa introduces a constraint, like dx/dt = k, by means of feedback and the property that its inputs are equal in voltage.
You can see this kx'' + x = 0, where the bottom and top chains form x'' and the feedback equals it to x.
You can also see it through the fact that d sin/dt = cos and dcos / dt = -sin
