Current Refernce: Poly current vs. PTAT current vs. constant-gm current

[Engineer4ever]

Hi,

I would like to know the difference between different current references techniques: PTAT current, poly current and constant-gm current. When do we use each one of them and why? and why do we use PTAT current in the first place? PTAT means that it will increase with increasing temp. so its temp. coeff. isn't zero, so what do we use it as a current reference?

Thanks in advance,

 

[dick_freebird]

PTAT is good when you want constant bandwidth against a
capacitance that rises with temperature, or constant gain
against a device whose gain may fall w/ temp (like MOSFETs).
You should work backward from the outcome you want and
the device vs-temp behaviors that would degrade it, to the
bias profile you want. You may want more than one in more
than one place.

"Reference" may or may not mean "constant".

 

[Engineer4ever]

Thanks for your reply.