Delete comment from: Ken Shirriff's blog
Thank you for the detailed explanation!
A minor contribution: I think the explanation for how the diff pair works is backwards (at least for the PNP example in the figure. It would be correct for an NPN diff pair).
The text says: "The basic idea is that a current mirror (the circle at the top) generates a fixed current I. This current gets split between the left path (I1) and the right path (I2). If the transistor on the left has a higher input voltage than the transistor on the right, most of the current will go to the left. But if the transistor on the right has a higher input, most of the current will go to the right."
For the PNP diff pair show, I think is the other way around: "If the transistor on the left has a higher input voltage [...] most of the current will go to the _RIGHT_"
Also, any though on why the bandgap resistors are 45 deg? Maybe something to do with the output stage heating up? Maybe it's just a way to improve matching? Avoid thermoelectric effects? Just curious of what other think/know about that.
Thank you!
Aug 19, 2021, 7:42:00 PM
Posted to Reverse-engineering a vintage power supply chip from die photos