M niknejad and b boser 20 capacitor applications

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Unformatted text preview: OS – Costly: large area (compared to FETs) – Nonidealities: • Large run-to-run variations • Temperature coefficient • Voltage coefficients (nonlinear) • Avoid them when you can – Especially in critical areas, e.g. • Amplifier feedback networks • Electronic filters • A/D converters – We will get back to this point EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 20 Capacitor Applications • Large value – Bypass capacitors – Frequency compensation • High accuracy, linearity – Feedback & sampling networks – Filters EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 21 Capacitor Options Type C [aF/µm2] VC [ppm/V] TC [ppm/oC] Gate 5300 Huge Big Poly-poly (option) 1000 10 25 Metal-metal 50 20 30 Metal-substrate 30 Metal-poly 50 Big Big Poly-substrate Junction capacitors 120 ~ 1000 EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 22 MOS Capacitor • High capacitance in inversion: – Linear region – Strong inversion • SPICE: I ωV V = 1V ω =1 →C = I C= EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 23 MOS Capacitor • High non-linearity, temperature coefficient • Useful only for non-critical applications, e.g. – (Miller) compensation capacitor – Bypass capacitor (supply, bias) EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 24 Poly-Poly Capacitor • Applications: – Feedback networks – Filters (SC and continuous time) – Charge redistribution DACs & ADCs • Cross-section • Bottom- and top-plate parasitics • Shields EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 25 Capacitor Layout • • • • Unit elements Shields: • Etching • Fringing fields “Common-centroid” Wiring and interconnect parasitics Ref.: Y. Tsividis, “Mixed Analog-Digital VLSI Design and Technology,” McGraw-Hill, 1996. EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 26 Metal Capacitors • Available in all processes (with at least 2 levels of metalization) • Large bottom plate parasitic – O...
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This note was uploaded on 03/18/2014 for the course EECS 240 taught by Professor Boser during the Spring '04 term at University of California, Berkeley.

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