Inductance negligible for small ic structures up to

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Unformatted text preview: chlib.nsf/techdocs/FE154539B8C4C01687256CD9007346D7/$file/180-nmCMOS3-24-04.pdf EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 35 Passives EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 36 www.ibm.com/chips/techlib/techlib.nsf/techdocs/FE154539B8C4C01687256CD9007346D7/$file/180-nmCMOS3-24-04.pdf Distributed Effects • Can model IC resistors as distributed RC circuits. • Transmission line analysis yields the equivalent 2port parameters. • Inductance negligible for small IC structures up to ~10GHz. EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 37 Effective Resistance • Rsh = 100 Ω/□, Cx=3.45×10-5 F/m2 • 10kΩ resistor drops to 5kΩ at 1 GHz ! (W=5µ) • High frequency resistance depends on W. Need distributed model for accurate freq response. EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 38 Capacitor Q • Current density in capacitor plates drops due to vertical displacement current. • Must analyze the distributed RC circuit… EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 39 Capacitor Impedance • For a capacitor contacted at one side, we can show that • We can simplify this for small structures EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 40 Double Contact Strucutre • Instead of doing distributed analysis, we can guess the current distribution as linear and quickly calculate the effective resistance. • For a double contact case, the resistance drops by 4 times. EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 41 On-Chip Inductors • Once in the domain of RF circuits, now inductors are finding applications in wideband design (e.g. shunt peaking). • By proper design, the bandwidth of the RC circuit can be boosted by 85% (20% peaking). EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 42 Spiral Inductors • These inductors are small (0.1-10 nH) and are used widely in RF circuits. • Use top metal for high Q and high self resonance frequencies. Very good matching and accuracy. EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 43 Multi-Layer Inductors Top view 3D view (not to scale) • By taking advantage of multiple metal layers and mutual coupling, we can realize very large inductors (~ 100 nH). EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 44...
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