construct a PTAT current source?

[shuiyun]

how to construct a PTAT current source using only the output voltage of the bandgap ? (can't use any of the internal nodes of the bandgap cell. Only it's output.)

 

[Syukri]

feed the output back to the R1 and R2 of the input

 

[shuiyun]

You can't use the node inside the bandgap ,only its output

 

[wchu01]

Try this:

1. Tie the reference voltage to the gate and a resistor at the source of the same transistor.

2. Use current mirror, mirror current flowing thru the transistor to where you need the current source.

My train of thought: With reference voltage, I can use that to regulate a drain current. Therefore fixing the drain current and using current mirror i can steer that to where i want.

 

[jwfan]

Level shift your voltage reference output with a bipolar transistor. Then you get
V2=Vref-Vbe, which is a PTAT voltage. Apply this voltage across a resistor. You can have a PTAT current.
BTW: Pay attention to the temperature coefficient of the resistor.