SOME QUESTION ABOUT PTAT AND BANDGAP IN RF CIRCUITS

[Youncen]

I know this is stupid question...but if I don't ask, I will be stupid not my question~~~ thank you first

what I wanna ask is which circuit need a ptat current bias

what circuit need bandgap

I have seen that most rf lna use ptat why? (to compensate the bjt's negetive Vbe? this will increase the gm!!!)
, but what if it is mixer or lo buffer.....

 

[Youncen]

nobody would help me?
I am waiting to preciate your help~

 

[drabos]

bandgap for mixers, VCO... they need reference voltage

 

[Youncen]

but why bandgap why ptat for example with respect to mos or bjt.... amp or mixer

 

[Jim cage]

you will need PTAT current into an amplifier to compensate for the temperature variations. for example, if the LNA gain is going down with temperature, then you would like PTAT current to bias the LNA and add extra current to increase the gain of the LNA.

for VCO's you would like to have its own LDO (band-gap) since it is most sensitive to supply and ground variations because it's high Kvco [MHz/V] and mainly due to mismatch.

Regards,
Jim