I need to implement a temperature sensor based on the circuit shown in the attached schematic. Unfortunately, the current flowing thru M1/M2 is not PTAT. So then how can I implement a temperature sensor based on this architecture? Any guidance will be helpful.
Hi,
Two transistors Q1 and Q2 with current sources are generate PTAT voltage Vbe1 - Vbe2 = Vt*ln(N).
I think that for this task you need to delete feedback and resistors, and get PTAT voltage VA - VB (you must setup dc point of current sources of M1 and M2 of cource).
It is not possible to remove R1, R2 as they are involved in generating the PTAT part of the bandgap output voltage as seen in the equation below. View attachment 90896
I think that is formula for output voltage of bandgap, which is independent from temperature and it got from assumption that Va = Vb.
And you may generate PTAT current only with two transistor (Q and nQ) and current sources.
"It is not possible to remove R1, R2 as they are involved in generating the PTAT part of the bandgap output voltage as seen in the equation below."
As seen in your equation, the PTAT portion (R3*ln(N)*Vt/R0) has no terms of R1 or R2. As FvM suggested, simply remove those resistors and you'll get a PTAT voltage.