ECL is old but still incredibly interesting. My interest is renewed after I found a few ECL databooks/appnotes/guides on eBay. Fairchild, Motorola, NatSemi... Some of those books are older than me (1972 for example) but still fascinating and particularly relevant for this project (and for #YGREC-ECL ) because they contain a lot of insight into the design process and the structures of the integrated circuits. The Motorola MECL book is particularly impressive as it explains the topologies, which would have taken years to invent myself...

For example, I know about "series gating" (serial connection/cascading of differential amplifiers) but this technique has some subtleties that the book explains, so I might implement a better-than-crude version. I found the same diagram on the web, thanks to knowing the right keyword :

The topology of the resistor-diodes networks on the right of the circuit is not something I would have imagined myself. The level adaptation on the left (transistor with base on X) is another non trivial circuit for me...

Right next to this circuit, another is shown that implements "dotting" where diff amps are paralleled, before driving the amplifier. This creates OR-AND networks and saves some latency.

This increases my "vocabulary" and I have more and better options for the design of discrete and fast digital circuits :-)

(note: a brief summary can be found there but nothing beats deadtree editions)