hard limiting

[Haible_Juergen#Tel2743]

>The simplest way to do it is to connect two back-to-back 9.1V zeners
>from the op-amp output to gnd. A more elegant solution would be to put
>the zeners in the feedback path of the op-amp. With these methods you
>*will* get rounded corners (at around 9.6V), but that's how analog
>components are.

I had to achieve very precise limiting in my Morphing Programmer
module. I also wanted to avoid the excessive noise of zener diodes.
I found a cheap "programmable zener", the TL431. It has a reference
of 2.5V inside that can be "transformed" by two resistors to any voltage
abpve 2.5V. The reference is actually a band gap and not a zener; so
You don't have the problems with noise and temperature drift, and it has
sharper corners also.

JH.