are the currents flowing in two legs of the BJT the same?
VBG=VEB2+Vtlnn(Rptat+R2+2Rtrim)/Rptat, correct?
why the out node connects back to the gate of M10, what's the vaule of VDD, will M10 turn-on?
Added after 15 minutes:
i think you can do DC analysis, and print the real vaule of each resistors, and see if the resistor ratio is the same as the ratio based on your hand caculation
It is suspicious that you have a bandgap curve at the wrong voltage. Is the startup circuit completely disconnecting after startup? Try it without the startup circuit and start it using initial conditions to check.
Rtrim is helping me if its type is different than Rptat R1 & R2.. i.e Rptat R1 & R2 are Ppoly than Rtrim is Npoly resistor. if all are same type than the value of constant voltage is again same. But i didnot understand why???
prcken said:
are the currents flowing in two legs of the BJT the same?
M10 wiil turn On .. its connected like this to control the start-up current
prcken said:
i think you can do DC analysis, and print the real vaule of each resistors, and see if the resistor ratio is the same as the ratio based on your hand caculation
the resistor ratio is slightly lesser then the calculated value
keith1200rs said:
It is suspicious that you have a bandgap curve at the wrong voltage. Is the startup circuit completely disconnecting after startup? Try it without the startup circuit and start it using initial conditions to check.
Keith
You shouldn't need to rely on the differential temperature coefficients of resistors to make a bandgap operate at the correct voltage. Something is wrong. What is the source of the design paper?
You shouldn't need to rely on the differential temperature coefficients of resistors to make a bandgap operate at the correct voltage. Something is wrong. What is the source of the design paper?
I got it from the book "Analog Design essentials" Willy sansen Pg 468
Where he says Rtrim is used to trim the value of bandgap to 1.2V. than only possibility i saw is using Rtrim a different resistor than others.(the attached paper made me to think in that direction)
PTAT current is equal to Vtlnn/Rptat, you can increase VBG with increasing the Rtrim value, i think not necessarily need to use different resistor type for Rtrim.
In the paper the different temperature coefficient resistor is in a different place to Rtrim in your circuit.
I don't have the book you mention, but the voltage of the bandgap should be close to 1.22V without trimming. Normally the trimming is to correct for mismatches due to processing variations. The nominal voltage with perfect matching should be correct without the trimming.
It might be worthwhile posting your circuit with device sizes & process.
Acctually, I got a 1.18V bandgap voltage by wafer data, but in that case, the PTAT is about 180nA. I think you can check your VBE. Is it equal to your hand calucation value?
Acctually, I got a 1.18V bandgap voltage by wafer data, but in that case, the PTAT is about 180nA. I think you can check your VBE. Is it equal to your hand calucation value?