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Problem with too high TC of a bandgap

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first,thank dkace for his great help for my layout.
but i hesitate the performance of my bandgap.
TC: 30ppm/Ci think it will be more terrible after Tape Out.i want to achieve TC: 10ppm/C。
i think the amp is critical in bandgap ,but i cannot grasp the point.how to simulation Av,psrr,stability and check the feedback of amp in the circuit?
 

Re: [HELP]Schematic of bandgap

Oh,i try to make the L of M17 large as 5um,the psrr is high,is it ok?is 5um too large?
but the psrr of the amp in the curcuit is abnormal.maybe the problem of amp or the simulation way.
So,the TC puzzle me.36ppm/c is bad.is there any improvement?the feedback of amp?i dont know how to solve.
 

Re: [HELP]Schematic of bandgap

5u is not that bad if your performance is good..

to improve tc, try to balance the resistor ratios..
 

[HELP]Schematic of bandgap

increase the capacitor's value,put r.c at the output can improve psrr.
also I think your current bias is not so good.
the cascode structure is good .
the cascode structure will consume many voltage and my PNP cannot work after 3V power supply?It can work well ,please try.I used the structure before.
 

[HELP]Schematic of bandgap

what is the function of the four MOSFETs in the ritht side,is it a startup ciucuit,can it work well?the two MOSFETs function as a compensition circuit in your opamp,does is work well,I really want to know the answer,can you tell me ,thank you sincerely
 

Re: [HELP]Schematic of bandgap

srieda said:
5u is not that bad if your performance is good..

to improve tc, try to balance the resistor ratios..
Click to expand...


thanks,srieda.

Added after 9 minutes:

zhangsai04 said:
increase the capacitor's value,put r.c at the output can improve psrr.
also I think your current bias is not so good.
the cascode structure is good .
the cascode structure will consume many voltage and my PNP cannot work after 3V power supply?It can work well ,please try.I used the structure before.
Click to expand...
thank you,zhangsai04.
increase the compensation capacitor to improve the phase mergin?what's r.c?
OK,i will try the cascode structure again.

Added after 5 minutes:

microbasly said:
what is the function of the four MOSFETs in the ritht side,is it a startup ciucuit,can it work well?the two MOSFETs function as a compensition circuit in your opamp,does is work well,I really want to know the answer,can you tell me ,thank you sincerely
Click to expand...
many thing impact the "work well"
 

Re: [HELP]Schematic of bandgap

now i think the psrri is ok.but the TC is not good.i think i should improve the amp,but have no idea in detail.
 

[HELP]TC of bandgap

put r.c at the output as a loop filter is a common use.In my opinion,your tc is ok.I guess your opamp maybe above 80db,the gain is enough too.then improve what?If you will tape out,I suggest use trimming.
 

Re: [HELP]TC of bandgap

zhangsai04 said:
put r.c at the output as a loop filter is a common use.In my opinion,your tc is ok.I guess your opamp maybe above 80db,the gain is enough too.then improve what?If you will tape out,I suggest use trimming.
Click to expand...
yes,my open-loop gain(A) is 80db,but my loop gain(AB) is poor,also the phase margin is strange.And i dont know how to simulation the feedback gain(B) and its phase.and i think this is the key to the problem.my TC is 35ppm,is it OK?
 

[HELP]TC of bandgap

There is a negative feedback here. You can simulate the openloop gain and phase margin.TC should accord with your specification which you made before design.
the following paper is almost the same with your design,have a look.
"A Sub-1-v 15-ppm/c cmos bandgap voltage reference without requiring low threshold voltage device"Ka Nang Leung,Philip K.T.Mok
If your PM is not enough,try a miller capacitor.
 

Re: [HELP]TC of bandgap

because the amp have two feedback path,i cut the output of the amp and add the Vac as 1V to simulate the loop gain ,but it's strange.i never see that before.
i think the feedback maybe have some problem,but i dont know how to simulate it.or maybe other problem.anyone help?
 

[HELP]TC of bandgap

you should cut off from net057 and net088--the drain(not the gate) of the M18,M15.
M17,M18,M15 must match very well!!!

Added after 7 minutes:

for improve TC
decrease the Vos of the opamp,see razavie's book.
 

Re: [HELP]TC of bandgap

i know the m15,m17,m18 should match well,but the drains' voltage of them is not equala and have no same TC.So the current cant be mirror absolutely.
this simulation way i will try. thanks indeed.
 

[HELP]TC of bandgap

did you add a cap at the output of amp when cut off? This cap is the total capacitance at the gate of M18. And I think it is better to put main polt at the output of amp, this will improve psrr. From your circuit, main pole is at output of first stage amp.

Added after 1 minutes:

please change x-axis to log, y-axis to db.
 

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