ho31.l28_bandgap

ho31.l28_bandgap - Lecture 28 28 Bandgap Reference R....

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Lecture 28 Bandgap Reference R. Dutton, Boris Murmann St f d U i it R. Dutton, B. Murmann 1 EE114 (HO #31) Stanford University Key Idea kT/q has a positive temperature coefficient – "PTAT" proportional to absolute temperature PTAT proportional to absolute temperature •V BE of a BJT decreases with temperature – "CTAT" complementary to absolute temperature Can combine PTAT + CTAT to yield an approximately zero TC voltage reference – Useful in circuits that require a stable reference voltage • E g A/D converters R. Dutton, B. Murmann 2 EE114 (HO #31) E.g. A/D converters
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 Conceptual Block Diagram R. Dutton, B. Murmann 3 EE114 (HO #31) (figure from text, Gray & Meyer; assuming conventional BJT technology with NPN and PNP) Simple CMOS Realization V DD R 1 R 2 I 1 I 2 V out R. Dutton, B. Murmann 4 EE114 (HO #31) n 1 Q 1 Q 2 (practical implementation in MOS technology; only substrate PNP available)
Background image of page 2
3 Recall the Substrate PNP A special twist that the technology provides: a three-terminal bipolar device with the collector (“C”) device with the collector (C) always connected to substrate p+ n-well n+ +V BE + V BE - qV V R. Dutton, B. Murmann 5 EE114 (HO #17) p-substrate space charge I S e BE kT I S β F e qV BE kT Typically β F >>1 hence the substrate component dominates EE114 (HO #31) +V BE I S e qV BE kT Diode-connected BJT (special case sub-PNP) Simplified Equivalent I S e qV BE kT F diode equiv. (special case sub PNP) +V BE I D = I S 1 + 1 F e qV BE kT qV BE R. Dutton, B. Murmann 6 I S e kT EE114 (HO #17) Solve for V BE as function of I S and I D EE114 (HO #31)
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
4 A Closer Look at V BE Et h h k T / i i t h t tV = S C BE I I ln q kT V (we’ll call the diode current I C ) Even though kT/q increases with temperature, V BE decreases because I S itself strongly depends on temperature C 0 0 G ) q / kT /( V 0 C BE I I ln q kT V e I I ln q kT V 0 G I S A Emitter n i 2 I S = f ( T ) e V G 0 kT / q I f ( T ) (details, EE216) R. Dutton, B. Murmann 7 EE114 (HO #31) I 0 is a device parameter, which is (unfortunately) not completely independent of temperature – We'll ignore this for now V G0 is the bandgap voltage of silicon "extrapolated to 0°K" 0 Extrapolated Bandgap 1.205eV V 205 . 1 q eV 205 . 1 V 0 G = = [Pierret, Advanced Semiconductor Fundamentals, p.85] R. Dutton, B. Murmann 8 EE114 (HO #31)
Background image of page 4
5 Temperature Coefficient of V BE
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 6
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 11/09/2009 for the course EE 114 at Stanford.

Page1 / 16

ho31.l28_bandgap - Lecture 28 28 Bandgap Reference R....

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online