Lately I was looking for very fast diodes to design faster DTL/TTL discrete gates.
- silicon epitaxial diodes can be quite fast but still have a limited frequency of rectification (particularly the cheap ones).
- As noted by @K.C. Lee on #YGREC-ECL : "Carrier mobility isn't as good as electrons. That's why NPN, N-MOSFET
have better performance than their PNP, P-MOSFET counterparts." so a complementary TTL gates, with a PNP input stage, would probably be speed-limited by the input transistors.
The recovery time makes a difference in several designs including switching power supplies. If you dig into the physics, there is a usually a trade-off between several other parameters and recovery time. Just to give you an idea, the datasheet for a BAT42 Schottky diode says the reverse recovery time at 10mA is no more than 5 ns."
I don't know the exact figures in practice in a logic gate but 5ns of recovery is not good. That's about the propagation time of a DCTL inverter in the CDC6600.
Rectification speed was already a burning subject in the 40s because it was essential to the war effort (faster diodes means higher carrier frequencies, shorter wavelengths and better radar resolution)
ECL prevents all these issues because
- there are only NPN transistors
- no diode (no recovery time)
- no saturation
However there are more transistors... so maybe DCTL is an interesting alternative ?