Delete comment from: Ken Shirriff's blog
Marc, the Motorola Databook discusses the advantages of the constant current source for ECL (p2). Older Motorola ECL chips (MECL 10K) used a resistor for the emitter current. But for the 10KH series, they added a voltage regulator and constant current source.
"The constant current source allows the use of matched collector resistors which produces better matched delays, matched output tracking rates with temperature and less variation in the output voltage level with changes in the power supply. There is also a considerable improvement in noise margins over MECL 10K."
For differential receivers, "the constant current source employed in the emitter node of the differential pair allows the increase in common mode rejection."
May 4, 2021, 6:19:44 PM