How can I achieve a current reference with a low ppm?

[liuguojia387]

How can I achieve a current reference with a low ppm if external resistance is NOT used?

 

[frankliner]

A voltage to current converter with an internal resistor and a ptat current sink (from the bandgap) in parallel. Then use final part trimming to center the current at room temp.

 

[liuguojia387]

A voltage to current converter with an internal resistor and a ptat current sink (from the bandgap) in parallel. Then use final part trimming to center the current at room temp.

if trimming cannot be used,how should I do?

 

[erikl]

if trimming cannot be used, how should I do?

Here's a circuit by which you can achieve a medium TC of ≈ 1000 ppm/K = 0.1 %/K :

 

[liuguojia387]

Thanks，But 1000ppm is a littile high?

 

[erikl]

... 1000ppm is a little high?

Depends on your need. Without external resistor or trimming, you probably won't achieve much better.

 

[dick_freebird]

If you have current mirror racks in your PTAT / bandgap,
then adding yet another mirror with a different combination
of emitter area and emitter resistor can produce yet another
temperature coefficient (more resistor makes current
TC less positive / more negative).

A MOS mirror rack might not be quite as well behaved,
don't know how consistent the TC behavior of Id/Vg
might be, to beat against resistor TC, over process.

 

[marcelom]

I have used a series ratio of two different TC (material) resistors to generate about 150ppm source. You just ratio the W/L's to achiece about 0 TC (typical parabola vs Temp curve).