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Bandgap Reference (I don't get how this analog amplifier thingy works)

SkyEyeSkyEye Registered User regular
edited November 2011 in Help / Advice Forum
Can someone please please explain why the voltage across a diode-connected pnp BJT in a bandgap reference is conditional to absolute temperature? I've been trying to work it out in my head and all I've got is Veb = Vt*ln (I/Is). Vt = kT/q, so the more hotter, the more differencier the potential right? I've thought about the "I" increasing with T but that also seems to make Veb bigger with temperature. What am I missing? Any help at all would be immensely appreciated, I feel so dumb right now thinking I would be able to eventually figure this out on my own.

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    tinwhiskerstinwhiskers Registered User regular
    In order for there to be a voltage difference there needs to be a resistance, the resistance is Vt(V=RI Veb=(R)ln(I/Is)). Been a few years since I took a semi-conductor class, but iirc and from the wiking i just did, VT is related to the mobility of the electrons in the boundary between the PNP layers. Its a physical effect caused by the materials having electrons, not any current you are or aren't applying.

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