I haven’t published a reference circuit, but a block diagram is fairly straightforward.
Here’s how I do it after trying many ways:
I tried lots of specialty high gain parts or integrated high gain VCA parts that were expensive and troublesome over the years. What works best in the end is just doing multiple stages after the VCA block, with 4x - 5x per gain stage, and use a separate op amp per stage. Two 5x stages in series it gives you a total gain of 25x, which gets a decently hard edge without going too crazy (this is about where Topogram sits for example.) Cadet II RGB Encoder is a good reference for a precision Black/White clipping circuit.