improved bandgap reference circuit design [help]

[gstekboy]

how to find values of R1 and R2 in below figure to get reference voltage(Vref) 1.262v.
W/L ratios are equal and area ratio for bipolar transistor is 10:1 .

 

[nitishn5]

You have a PTAT voltage across R1.
V_PTAT = (KT/q)ln(m)
This would fix the current in the PMOS current mirrors as a PTAT current,
I_PTAT = V_PTAT/R₁

Your Output Voltage V_ref = (I_PTATR₂) + V_BE,q3

Now adjust R2 to get V_ref as constant across temperature as possible.

You might require a few iterations to get to the final value.
If R2 becomes too large, try increasing the PTAT current by reducing R1.

One easy technique is to plot the slopes of the CTAT voltage and the -1*m*PTAT Voltage over each other and find the value of the multiplier m for which the slopes match. m = R2/R1

 

[gstekboy]

You have a PTAT voltage across R1.
V_PTAT = (KT/q)ln(m)
This would fix the current in the PMOS current mirrors as a PTAT current,
I_PTAT = V_PTAT/R₁

Your Output Voltage V_ref = (I_PTATR₂) + V_BE,q3

Now adjust R2 to get V_ref as constant across temperature as possible.

You might require a few iterations to get to the final value.
If R2 becomes too large, try increasing the PTAT current by reducing R1.

One easy technique is to plot the slopes of the CTAT voltage and the -1*m*PTAT Voltage over each other and find the value of the multiplier m for which the slopes match. m = R2/R1

Sir , there is no pmos current mirror in the circuit.

 

[nitishn5]

The Op-Amp sets the bias for the PMOS devices at the top i.e. M1, M2, M3, M4, M5. These all now have the same PTAT current(assuming they are all sized the same).
These are what I was referring to.