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Simple one-stage amplifier QUESTION~

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ljy4468

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hello everyone~
I've a question about the attatched circuit.
It is a simple one-stage amplifier.

But what's the role of two PMOS at the middle of the picture????
Anyone give me the answer of tell me some correlated article, please?

Thanks
Regards.
 

It should be dummy. I thick. For layout process variation consideration
 

I'm not so sure -- why would you want to add some PMOS devices for matching? Could they be there to implement a capacitor?
 

It must be dummy tr for matching.
Hi jaeyoung. ha ha ha
 

ljy4468 said:
hello everyone~
I've a question about the attatched circuit.
It is a simple one-stage amplifier.

But what's the role of two PMOS at the middle of the picture????
Anyone give me the answer of tell me some correlated article, please?

Thanks
Regards.
Click to expand...

It must be dummy
 

lladnar23 said:
I'm not so sure -- why would you want to add some PMOS devices for matching? Could they be there to implement a capacitor?
Click to expand...

Those are dummies and the way they are connected also adds their Cgd capacitance to the output, not a good idea for high speed design, but it is ok for low frequencies. I assume that circuit is for low frequencies, judging by the channel length used and by the fact that input devices are 5 pieces (or fingers) in parallel.
Why are the dummies needed - to improve matching of the differential pair. If you leave the diff pair without dummies then the end fingers will see different surroundings than the middle ones. With dummies you avoid this. Also in newer processes, using shallow-trench isolation you need to put dummies because the devices at the end will see different mechanical stress conditions than the middle ones due to the trench formation.
 

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