why PTAT current reference is used to bias some circuits?

[lgqfang]

rbic ptat

hi ,guys
as I know, PTAT current reference is often used to bias some circuits. what kinds of circuits need PTAT current to bias and why?
thank you!

 

[mpig09]

ptat current

Dear lgqfang :


When you need reference voltage or current, you need PTAT current !!


mpig

 

[szekit]

process independent ptat bias

to the first order, current is proportional to mobility of electrons and mobility decreases as a function of temperature. if current decreaes with temperature, gm decreases also. hence, PTAT reference is used. of course there is also constant gm reference circuit.

 

[gte582w]

Re: why PTAT current reference is used to bias some circuits

a comment on szekit's reply: For BJT, gm=Ic/Vt, where Vt is PTAT, so if
your Ic is also PTAT, then you gm will be independent to temperature.

 

[rajkumaru]

Re: why PTAT current reference is used to bias some circuits

purpose of using reference circuit is reference should be independent of
- temperature
- supply voltage
- process parameter i.e., mobility