Dummy transistors - their role in a circuit

[MANIpal]

dummy transistors

In many circuits, I have found dummy transistors (specially in current mirror circuits)!!!
can anyone tell me why do we need that?
whether these dummy transistors are added to improve the layout?

 

[betwixt]

Re: Dummy transistors!!!!!!!!!!!!

Most likely the transistors are part of an array of matched devices where there are more in the package than needed for the design. In current mirrors the transistors have to be matched and often it is cheaper to buy a matched array and not use some of them than to select the required number of matched ones manually.
Brian.

 

[millwood]

Dummy transistors!!!!!!!!!!!!

those dummy transistors are simply not smart enough to work in a circuit. that's why they are dummies.

 

[ME]

Dummy transistors!!!!!!!!!!!!

Read this: https://en.wikipedia.org/wiki/Current_mirror

 

[eecs4ever]

Dummy transistors

Transistors near the edge of an array could be doped differently than transistors away from the edge. Thus, for best matching , its good to put dummy transistors on the edge.

Also, the transistor gates near the edge may be etched at a different rate, resulting in a variation in gate length.

lol @ millwood's response

 

[deepak242003]

Dummy transistors

Dummies are added at the end so that each transistor experiences the same surroundings... thus reducing poly etch varation.....

In DSM, it is also helping to reduces STI stress effect....

 

[mbyoussef]

Re: Dummy transistors

They are also used to account for the edge proximity effect and well proximity effect