why use a ptat or bandgap bias

[Youncen]

ptat bias

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]

lna ptat bias

no one respond........ but I will wait

 

[memsgg]

I have the same question, can anyone answer it?

In specially, if a opamp's bias current is 300uA, can we directly use a current generator to connect it while testing?

thanks advance

 

[Youncen]

ok already know why from a direct hand design experence....thanks and no need for further help,it seems not many real engeer stroll around here

 

[mydreamhouse]

if your need a referece , your need the bandgap

 

[gte582w]

Youncen: for BJT, if IC is ptat, than it's gm will stay
constant which is important to stablize your circuit's
performance.