questions on current source

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sidang

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hi..sorry if i ask basic questions..

1. why normally pmos use as current source instead of nmos

2. how to prove high output impedance can help provide constant current even
though Vdd vary.
 

Hi,

I guess PMOS is usually used because then the load can be referenced to ground. With an NMOS circuit, the load usually has to be floating since you would normally connect the source to ground.

Regards,
Chris
 

1. As I know PMOS usually used as current source as load resistance for NMOS
stage amplifier ( to obtain higher amplification gain )

2. I think this is not ture. Just we can prove that we have constant
current even though load resistance vary.
provided that load resistance voltage not exeeded (Vdd-Vds min)
I mean voltage change may change current value.
 

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