lhlbluesky
Banned
i have designed a ptat bandgap,which is current mode,that is,vref is generated by only a resistor,and the current is consisted of vbe2/r2+deta(vbe)/r1,so
vref=(vbe2/r2+deta(vbe)/r1)*r3;i don't know whether it is clear;
my question is, i use csmc 5v high voltage process,and when i simulate the temp coeffient,i find that when in -4~85, the voltage change in tt\ss\ff is all about 6mv;when in -40~150(my required operating temp range) ,the voltage change in tt\ss\ff is different,tt \ss is 48mv or so,ff is 120mv or so;and when i adjust the value of r1\r2\r3 to make tc small in tt,then in ss or ff,tc becomes too bad,about 260mv;why? what's the reason?
besides,when i sweep vdd from 0 to 5v,i find that the value of vref becomes v1 when vdd is 2.8v or so,and becomes v2(the desired value of vref,and v1<v2)when vdd is 4.4v or so;why?as usual,the value of v1 for vdd=2.8V~4.4V should not appear, it should become v2(desired value of vref)when vdd=3v or so;but why for my circuit?i think it for two days,but get nothing.pls help me.
vref=(vbe2/r2+deta(vbe)/r1)*r3;i don't know whether it is clear;
my question is, i use csmc 5v high voltage process,and when i simulate the temp coeffient,i find that when in -4~85, the voltage change in tt\ss\ff is all about 6mv;when in -40~150(my required operating temp range) ,the voltage change in tt\ss\ff is different,tt \ss is 48mv or so,ff is 120mv or so;and when i adjust the value of r1\r2\r3 to make tc small in tt,then in ss or ff,tc becomes too bad,about 260mv;why? what's the reason?
besides,when i sweep vdd from 0 to 5v,i find that the value of vref becomes v1 when vdd is 2.8v or so,and becomes v2(the desired value of vref,and v1<v2)when vdd is 4.4v or so;why?as usual,the value of v1 for vdd=2.8V~4.4V should not appear, it should become v2(desired value of vref)when vdd=3v or so;but why for my circuit?i think it for two days,but get nothing.pls help me.