Transcript Chapter 1
CMOS Analog Design Using All-Region MOSFET Modeling Chapter 1 Introduction to analog CMOS design CMOS Analog Design Using All-Region MOSFET Modeling 1 Important differences between BJTs and MOSFETs A) BJTs are three-terminal devices and MOSFETs are four-terminal devices B) Differences in the internal symmetries of the most commonly used BJTs and MOSFETs C) BJT exponential current law vs. MOS current law D) The geometric degrees of freedom for MOSFETs in analog design E) Quality of BJT and MOSFET models CMOS Analog Design Using All-Region MOSFET Modeling 2 Ebers-Moll equivalent circuit of an npn transistor Forward and reverse currents IE E IC F I F I R RIR FIF DE DC IF IB IC C IR B I E R IR I F I B ( IC I E ) (1 F ) I F (1 R ) I R CMOS Analog Design Using All-Region MOSFET Modeling 3 The capacitive model of the MOS structure depletion VGB region s p- type neutral region VGB Cox Cb s ds Cox 1 dVGB Cox Cb n CMOS Analog Design Using All-Region MOSFET Modeling 4 MOSFET: symmetric strong and weak inversion models VDB VGB VSB ID n+ n+ p-type substrate strong inversion I F ( R) V 2n GB weak inversion ID IF IR nVSB ( DB ) VT 0 2 I F ( R) W VGB VT 0 nVSB ( DB ) / nt I0 e L W Cox L CMOS Analog Design Using All-Region MOSFET Modeling 5 Intrinsic gain stages: common-source and common-emitter amplifiers CMOS Analog Design Using All-Region MOSFET Modeling 6 Small-signal circuit and frequency response of the CS and CE amplifiers gm vo vi ; jCL b gm u CL CMOS Analog Design Using All-Region MOSFET Modeling 7 Design of the CE and CS amplifiers Av u 1 gm uCL 2 GB CL BJT VBE /t IC I S e IC gmt 2 GB CL t MOSFET I Dsi 1 W 2 Cox VGB VT 0 nVSB 2n L I Dsi CMOS Analog Design Using All-Region MOSFET Modeling ngm2 2Cox W / L 8 Example: GB = 10 MHz, CL = 10 pF Cox = 80·10-6 A/V2, n = 1.35 gm 2 GB CL 628 A/V W/L 500 100 50 10 IDsi (A)1 0 6.6 33.2 66.4 332 ID (A)2 22 28.6 55.2 88.4 354 1 Strong inversion model. 2 Accurate allregion MOSFET model CMOS Analog Design Using All-Region MOSFET Modeling 9 All-region “empirical” model of the MOSFET I D 22 μA I Dsi IWI ngmt 1.35 628 106.26 103 22 μA I D IWI I Dsi I D IWI gm ng mt 1 t W / L 2 Cox W / L th 1 W / L gm W / Lth 2Cox t CMOS Analog Design Using All-Region MOSFET Modeling 10 Aspect ratio vs. current excess in a MOSFET design I D IWI W / L th 1 W / L CMOS Analog Design Using All-Region MOSFET Modeling 11 Consistent modeling of MOSFETs and the series association I D W / L eq g VG ,VS g VG ,VD W / L S W / L D W / L eq W / L S W / L D CMOS Analog Design Using All-Region MOSFET Modeling 12 Series-parallel association of MOSFETs CMOS Analog Design Using All-Region MOSFET Modeling 13 Series association of MOSFETs vs. long-channel MOSFETs Series association Long-channel Nominal VT L-dependent VT Characterize one L-dependent characterization transistor ( performance of (halo/pocket implants effects) the shortest transistor is “optimized”) “Accurate” for current mirrors L-dependent accuracy Gate current more predictable Extrinsic capacitors at intermediate nodes CMOS Analog Design Using All-Region MOSFET Modeling 14 Application of series parallel associations of MOSFETs - M:1 current mirrors M Iin : 1 M IO : 1 IO Iin M M N : 1/ M IO N M Iin N M M CMOS Analog Design Using All-Region MOSFET Modeling 15 Current mismatch of two M:1 current mirrors Iin 100 : 1 IO 100 100 : 1 IO Iin 10 N 100 10 Arnaud, JSSC Sep. 06 CMOS Analog Design Using All-Region MOSFET Modeling 16 M-2M Digital-to-Analog converter (1): A set of 4 transistors can be used as substitute for Mbb ID1 ID2 Mc Md ID Mbc VG Ma Mba ID1 ID2a Mbd Mbb ID2b CMOS Analog Design Using All-Region MOSFET Modeling 17 M-2M Digital-to-Analog converter (2): 8 bit DAC with M-2M ladder IB VB VR IR MB1 M71 MB2 M72 M73 M61 M64 M01 M04 M62 M63 M02 M03 M00 Q7 -Q7 Q6 -Q6 Q0 -Q0 -Q7 Q7 -Q6 Q6 -Q0 Q0 I0 V0 IG VG GB Q7 Di D ck Q Q6 D ck Q Q1 D ck Q Q0 D Q Do ck Ck CMOS Analog Design Using All-Region MOSFET Modeling 18 M-2M Digital-to-Analog converter (3): Model of the normalized current mismatch for a 10 μm x 10 μm transistor CMOS Analog Design Using All-Region MOSFET Modeling 19 M-2M Digital-to-Analog converter (4): CMOS Analog Design Using All-Region MOSFET Modeling 20 M-2M Digital-to-Analog converter (5): Top area is the M-2M ladder and the bottom area is the serial register. Klimach, ISCAS 08 CMOS Analog Design Using All-Region MOSFET Modeling 21 Similar approaches to CMOS design Paul G. A. Jespers; The gm/ID Design Methodology for CMOS Analog Low Power Integrated Circuits 2009, ISBN: 978-0-387-47100-6 D. M. Binkley; Tradeoffs and Optimization in Analog CMOS Design ISBN: 978-0-470-03136-0, Wiley 2008. Danica Stefanovic and Maher Kayal; Structured Analog CMOS Design Series: Analog Circuits and Signal Processing 2009, ISBN: 978-1-4020-8572-7 CMOS Analog Design Using All-Region MOSFET Modeling 22