问 The first tapeout ICs hrpoly resistor's unit value is 1.7k/um, the bandgap value is about 1.20V to 1.23V; and the second tapeout I only changes the metal 2 and metal1 mask, the bandgap block doesn't make any changes, but unluckily the process changes mainly that hrpoly resistor's unit value changes to 2k/um, so all the resistors' value used in bandgap block increase. When the second tapeout ICs comes back, the bandgap's value changes to about 1.23V to 1.26V.
I really CAN't understand why the result is so because the R1/R2 ratio CAN CANcel the resistor's unit variation.(The simulation also shows that). Of course, the bandgap PTAT changes smaller, but does it cause the problems? Or any other reason? Thank you for your instruction. 答 1: -.-"BSUGenerally speaking,we hold a view that the voltage drop p-n juntion equalized to a constant at absolute zero ,which named Vgo,and we should've got Vgo=1.205 V for material of silicon.
Actually,we would like to get a bandgap soure Vref=N*Vgo(analysis with N=1).For tyPICal IC of bipolar, when the temperature has been changed,the equation equalized to Vref=Vg0-C*T+M*Vt(constant C,M and thermal voltage Vt),also should we ensured the effect between  constant M and the resistor vlaue which you pointed out,yet,C*T=M*Vt,
so Vref held value of Vgo.