{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Lect2UP060_(100324)

# Lect2UP060_(100324) - Lecture 060 Capacitors Page 060-1...

This preview shows pages 1–4. Sign up to view the full content.

Lecture 060 – Capacitors (3/24/10) Page 060-1 CMOS Analog Circuit Design © P.E. Allen - 2010 LECTURE 060 - CAPACITORS LECTURE ORGANIZATION Outline • Introduction pn junction capacitors • MOSFET gate capacitors • Conductor-insulator-conductor capacitors • Deviation from ideal behavior in capacitors • Summary CMOS Analog Circuit Design, 2 nd Edition Reference Pages 43-47, 58-59 and 63-64 Lecture 060 – Capacitors (3/24/10) Page 060-2 CMOS Analog Circuit Design © P.E. Allen - 2010 INTRODUCTION Types of Capacitors for CMOS Technology 1.) PN junction (depletion) capacitors 2.) MOSFET gate capacitors 3.) Conductor-insulator-conductor capacitors 060204-01 + - v D x d W 2 W 1 + - + - + - + - + - + - d 060207-01 p -well p + G D,S,B n + n + C ox C junction Top Conductor Bottom Conductor Dielectric Insulating layer 060206-02

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

View Full Document
Lecture 060 – Capacitors (3/24/10) Page 060-3 CMOS Analog Circuit Design © P.E. Allen - 2010 Characterization of Capacitors What characterizes a capacitor? 1.) Dissipation (quality factor) of a capacitor is Q = ± CR p = C R s where R p is the equivalent resistance in parallel with the capacitor, C , and R s is the electrical series resistance (ESR) of the capacitor, C . 2.) Parasitic capacitors to ground from each node of the capacitor. 3.) The density of the capacitor in Farads/area. 4.) The absolute and relative accuracies of the capacitor. 5.) The C max /C min ratio which is the largest value of capacitance to the smallest when the capacitor is used as a variable capacitor ( varactor ). 6.) The variation of a variable capacitance with the control voltage. 7.) Linearity, q = Cv . Lecture 060 – Capacitors (3/24/10) Page 060-4 CMOS Analog Circuit Design © P.E. Allen - 2010 PN JUNCTION CAPACITORS PN Junction Capacitors in a Well Generally made by diffusion into the well. Anode n-well p + Substrate Fig. 2.5-011 n + n + p + Depletion Region Cathode p - substrate C j C j R wj R wj R w C w R s Anode Cathode V A V B C R wj r D Layout: Minimize the distance between the p + and n + diffusions. Two different versions have been tested. 1.) Large islands – 9 μ m on a side 2.) Small islands – 1.2 μ m on a side n -well n + diffusion p + dif- fusion Fig. 2.5-1A
Lecture 060 – Capacitors (3/24/10) Page 060-5 CMOS Analog Circuit Design © P.E. Allen - 2010 PN -Junction Capacitors – Continued The anode should be the floating node and the cathode must be connected to ac ground. Experimental data ( Q at 2GHz, 0.5 μ m CMOS) : 060206-03 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 3 3.5 C Anode (pF) Cathode Voltage (V) Large Islands Small Islands C max C min 0 20 40 60 80 100 120 0 0.5 1 1.5 2 2.5 3 3.5 Q Q min Q max Large Islands Small Islands Cathode Voltage (V) R-X Bridge Anode Cathode Cathode Voltage C R-X Bridge Anode Cathode Cathode C Small Islands (598 1.2 μ m x1.2 μ m) Large Islands (42 9 μ m x 9 μ m) Terminal Under Test C max / C min Q min Q max C max / C min Q min Q max Anode 1.23 94.5 109 1.32 19 22.6 Cathode 1.21 8.4 9.2 1.29 8.6 9.5 E. Pedersen, “RF CMOS Varactors for 2GHz Applications,” Analog Integrated Circuits and Signal Processing , vol. 26, pp. 27-36, Jan. 2001.

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

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 17

Lect2UP060_(100324) - Lecture 060 Capacitors Page 060-1...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online