I want to construct a lowpass digital differentiator with uniform-interval samples such that error from ideal differentiator is $n$ dB in magnitude at maximum for the passband up to frequency $\omega_c$. (The reference for dB here is amplitude of $1$.)
This error magnitude is not magnitude of frequency response of a lowpass differentiator subtracted from magnitude of frequency response of an ideal differentiator. The error magnitude literally is magnitude of the subtraction of frequency response of a lowpass differentiator from frequency response of the ideal differentiator.
Also, I want the lowpass differentiator to roll off close to zero for frequency response of frequency from $\omega_c$ to $\pi$.
It is hard to find an article that shows how to construct such a filter as a function of $n$ and $\omega_c$. Can anyone show me any reference? There surely must be such a filter construction. I do not care if it is IIR or FIR filter, Savitzky-Golay or not, though the error magnitude restriction seems to favor zero-phase filters such as Savitzky-Golay.