source follower buffer current

[nisha gupta]

plz tell me hw much current is required in source follower buffer. i design a source follower buffer , when i m putting it at the output of downconversion mixer, if i m not putting capacitor at the o/p of buffer o/p waveform is not cmng corrent. when i m not putting capacitor it is cmng correct but current is very hign aroung 19mAbut it is not giving desired result. and it is a diffential source follower buffer terminated by differential to single ended rflib balun in cadence as well 50ohm port.

 

[snishanth512]

What opamp are you using???

 

[nisha gupta]

i hv designed using NMOS. i hv'nt use OPAMP

 

[kam1787]

need to see the circuit

 

[nisha gupta]

i hv used 2 NMOs in a leg, bottom mos is current source and signal is driven to top mos.

 

[vfone]

In NMOS source follower when Vbs is not zero, the linearity is low because of the body effect. Increasing current doesn't help too much.
So, in this situation is better to do not use a source follower if linearity is important.