Paul
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Hello everybody,
trimming is indeed relatively expensive in production and that's what makes the cost of very precise voltage references. What is important when considering trimming is that you must be able to perform the compensation by measuring the voltage at a single temperature (ideally room temperature of course). If you need to measure the voltage at more than one temperature, you need to perform interpolation and the trimming algorithm becomes complex, thus even more expensive.
By the way, you should be aware that corner simulation does not take into account device mismatch, which will directly affect the stability of the bandgap voltage over temperature. The BJT matching is intrinsically good, but you should have a look at the influence of resistor and MOSFET matching on your Vbg(T) characteristic. Some people use mismatch compensation schemes, like chopping or auto-zeroing, to solve this problem, but it needs some area-expensive low-pass filtering.
Paul
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