why want high output resistance

[1a2s3d4f]

Hi everyone,

comparing the simple current mirror with the cascode current mirror, the cascode current mirror has high output resistance. why do we want to have high output resistance. I understand that ideal current source has constant output resistance. how is this relate to the cascode current concept.

thank you

 

[aProgrammer]

wrong,

ideal current source has infinite output resistance

 

[Btrend]

the higher output resistance, the smaller loading effect of ur current source, and the more accurate of the mirror current.

 

[acbalbason]

hi!

higher output resistance results in higher gain:

|Av| = gm1{gm4 ro4 ro5 || [gm3 ro3 (ro1 || ro2)]}

**broken link removed**

- al

 

[Yahia Muhammad]

we need high output impedance ideaally so that the current becomes constant ( not increasing like the mosfet response)

 

[rob1012]

ideal current mirrors have infinite output resistance so as to mirror exactly the same current as the source... the higher the output resistance the more accurate your mirror becomes.

 

[122013137]

ideal current mirrors have infinite output resistance

 

[1a2s3d4f]

thank you all for reply,

I understand the reason why we want to make the output resistance high. the reason is that we want to get it as closer as possible to ideal current sourse.

thank you all.

 

[fuweidavid]

on the other hand
we should do some tricks to cascode to lower down the output voltage by adding a soure on the gate of the cmos