M niknejad and b boser 20 extrinsic mos capacitances

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Unformatted text preview: F saturation : C gs = 2 C gc + Col = 201fF 3 C gd = Col = 24fF EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 19 Layout HSPICE geo = 0 (default) HSPICE geo = 3 EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 20 Extrinsic MOS Capacitances • Source/drain diffusion junction capacitance: C j (V ) ≅ Cbc 0 = • C j0 V 1 + V b ε Siε 0 x j0 m and with C jsw (V ) ≅ x j0 = C jsw0 V 1 + V b m 2ε Siε 0 Φ bi qe N sub fF µm 2 fF C jswn 0 = 0.49 µm 2 Vbn = 0.51V C jn 0 = 0.85 mn = 0.39 fF µm 2 fF C jswn 0 = 0.48 2 µm Vbn = 0.93V C jn 0 = 1.1 mn = 0.48 Example: W/L = 100/0.5, VSB = VDB = 0V, Ldiff = 1µm AS = AD = 100µm2, PS = PD = 102µm Cjn = 85fF Cjswn = 50fF Cbc = 58fF Strong Inversion – Saturation: Csb = 173fF Linear region: Csb = 164fF EECS 240 Lecture 2: CMOS - passive devices Cdb = 135fF Cdb = 164fF © 2006 A. M. Niknejad and B. Boser 21 High Frequency Figures of Merit • Unity current-gain bandwidth (Long channel model) • This is related to the channel transit time: • For degenerate short channel device EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 22 Efficiency gm/ID versus fT versus 0.35u Process Speed-Efficiency Tradeoff NMOS faster than PMOS EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 23 Weak Inversion Frequency Response • The gate capacitance in weak inversion is given by • IM is the maximum achievable current in weak inversion so the factor ( ) < 1 Ref: Tsividis, Operation and Modeling of the MOS Transistor EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 24 Device Scaling 60 50 0.18µm fT [GHz] 40 30 0.25µm 20 0.35µm 0.5µm 10 0 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 VGS-VTH [V] Short channel devices are significantly faster! EECS 240 Lecture 2: CMOS - passive devices © 2006 A. M. Niknejad and B. Boser 25 Device Figure-of-Merit 400 0.18µm 350 fT⋅ g m/ID [GHz/V] 300 250 200 0.25µm 150 0.35...
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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 Berkeley.

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