question about NPN match

[borislee]

Which of following matchs best to a singal NPN transistor with the relationship of 1:N? And which one is the worst?
1. n NPN transistors. In layout, the n transistors can be put together and beside the signal transistor, but cannot put around the singal one.
2. a NPN transistor, with n emitters. Each emitter and the base, the collector has the same area to the corresponding area of the singal transistor.
3. a NPN transistor, the area of the emitter is n times of that of the singal transistor.

 

[jwfan]

I prefer the first one. But if the layout budget is limited, the second one.

 

[borislee]

Thanks to jwfan

would you please explain your answer? I am not familiar with bipolar process.

 

[sunking]

the first one have the same Rbe

 

[huojinsi]

The first one is my preference. The reason is all the transistor's shape and size is same, so the characteristic of every transistor is almost same, and the consistence and symmetry is very good to match, but it occupys many area.

 

[borislee]

thanks to sunking and Huajinsi

And how about the second choice and the last one? which one is better and why?

 

[marshel]

Compared to the 2nd and the 3rd, the 2nd is better. For the 2nd have the same ratio of area and perimeter of emitter base and collector.