How is Emitter Coupled Logic different from Current Mode Logic. I have seen written in "Microelectronics Circuits" by Sedra Smith that CML is based on ECL . If it is so can anybody explain how they are related?
\$\begingroup\$
\$\endgroup\$
2
-
\$\begingroup\$ They are effectively the same in a broad sense, see Wikipedia. Maybe a particular author makes a distinction in his book, but that's not general knowledge. \$\endgroup\$– Dmitry GrigoryevJun 3, 2015 at 12:32
-
\$\begingroup\$ You could say that ECL is a possible implementation of CML. One could make an ECL-based circuit but with MOSFETs instead of BJTs. Then you wouldn't call it ECL as there are no emitters ;-) \$\endgroup\$– BimpelrekkieJun 3, 2015 at 12:43
Add a comment
|
1 Answer
\$\begingroup\$
\$\endgroup\$
2
THis is an ECL circuit. Notice the output is from the emitters of two BJTs:
(source: Wikimedia)
This is a CML circuit:
(source: Wikimedia)
Notice the outputs are from the collectors of two BJTs.
explain how they are related?
The CML output is essentially the ECL output with the emitter followers taken away.
What does this mean in applications?:
ECL outputs require pull-down resistors to bias the output buffers correctly. CML does not.
ECL outputs can be combined in wired-OR configuration; CML outputs can not.
CML outputs are 50-ohm matched. ECL outputs are low-impedance and require series termination if they need to be matched (which reduce signal swing). Typically ECL is run with matched termination at the load only.
CML's common mode level tends to be very near VCC. ECL's is about 1 V below VCC.
answered Jun 3, 2015 at 15:38
-
\$\begingroup\$ And one more thing please, what is so special about CML/ECL logic family than others? \$\endgroup\$ Jun 10, 2015 at 8:35
-
\$\begingroup\$ @AbhishekTyagi, you could ask that as a new question. It probably would help to specify what other logic families you want to compare with. \$\endgroup\$ Jun 10, 2015 at 18:38