while doing matching why do we need to consider the direction of current flow?

[ms_90]

when i was reading some docs about matching,it has been mentioned that while doing transistor matching in diff pair we need to consider the direction of current flow.
why this is important? can someone please explain it in detail?

 

[D.A.(Tony)Stewart]

If the current gain is not equal, a differential output voltage will exist for an equal input current.

This is even more important if only a single ended output is used and current mirrors are used with a different Vbe characteristic. Some more info here https://en.wikipedia.org/wiki/Differential_amplifier#Emitter_constant_current_source

Matching on the same chip gives much better results than using discrete parts.

 

[crutschow]

Is this taking about the layout of matched transistors in an analog IC chip design?