Eecs 240 lecture 8 references 2006 a m niknejad and b

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Unformatted text preview: a VBE as a reference. VBE is very insensitive (logarithmically) to current variations. EECS 240 Lecture 8: References © 2006 A. M. Niknejad and B. Boser 5 Improved VGS/VBE Reference • Now we have only one VBE (VGS) as the reference. If the overdrive of the MOS is small relative to VT, this is a threshold reference. EECS 240 Lecture 8: References © 2006 A. M. Niknejad and B. Boser 6 Peaking Current Source • Useful for very small (nA) current levels. • Can compensate for variations in VGS with a resistor to produce first order supply independent. EECS 240 Lecture 8: References © 2006 A. M. Niknejad and B. Boser 7 Widlar Reference DC Analysis DC1 Device Iref sweep from 0 to 300u (200 steps) 3V 3.2 3.5 3 R1 2.5 10kOhm Q1 2 Q2 I C2 1.5 1 Iref Vout 0.5 0.05 0 0 0.055 VBE1 = VBE 2 + R1 I C 2 I ref Vt ln I s1 I = Vt ln C 2 + R1 I C 2 I s2 EECS 240 Lecture 8: References 200 400 600 800 1000 I ref ( I C2) 1200 1400 1600 1800 2000 3 1.926×10 • IC2 is “relatively” insensitive to Iref • first order supply independence © 2006 A. M. Niknejad and B. Boser 8 PTAT Reference DC Analysis DC1 Device VDD sweep from 10m to 3 (199 steps) I I ∆VBE = Vt ln s 2 C1 I I s1 C 2 R1 10kOhm delta_Vbe Q1 I C1 = Vt ln M I C2 ∝T Q2 Q2 M=8 VDD M1 10 / 1 M2 10 / 1 VSS Issues: • • • • • EECS 240 Lecture 8: References Cascoding Self...
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