Download SHANGHAI JIAO TONG UNIVERSITY School of Microelectronics

SHANGHAI JIAO TONG UNIVERSITY
School of Microelectronics
Fall 2012, Dr. Guoxing Wang
Homework 2
Due date: 2012/10/09
 Use A4 paper to write/print your answer.
 Your name and student ID on the cover page.
 Language: English.
 Staple the pages.
Q1: Referring to the library file (log018.l), calculate CGS and CGD of nch.1 and pch.1 in
three different regions (cutoff region, linear region and saturation region) respectively,
choose W/L=9u/0.18u.
Q2: The circuits are shown in Fig2.1 and Fig2.2 respectively. Vx changes from 0 to
3.3V. (Hints: The Drain and Source of the transistor are exchangeable depending on the
applied voltages.)
 Draw rough IX-VX curves of Fig2.1 and Fig2.2 respectively.
 Draw rough gm-VX curves of Fig2.1 and Fig2.2 respectively.
 Use cadence to verify the curves you drew.
IX
+
VX
M1
+1.9V
+
+1V
Fig2.1
-
IX
+1.5V
M2
+1.9V
+
+
+1V
-
VX
-
Fig2.2
Q3: The circuit shown in Fig.3 is widely used as a NMOS inverter before the CMOS
process came into being.
 Please point out the differences between the NMOS inverter and the CMOS
inverter and give your explanations why the NMOS inverter is now almost
completely replaced by the CMOS inverter.
 Designate the sizes of M1 and M2 at your will and simulate Fig.2 by Hspice. Draw
the transfer characteristic curve (Vout versus Vin) of the circuit, use the curve to
calculate VIH ,VOH,VOL,VIL and the noise margin of the inverter. Your simulating
codes need to be attached.
 Calculate the rise time tr and the fall time tf of the inverter if ID is a constant .
Adjust the sizes of the two transistors to get tr=tf .
3.3V
M1
Vout
Vin
M2
50fF
Fig3
Q4: As we all know, a MOSFET can work in three regions: sub-threshold region, linear
region and saturation region.
 Calculate the transconductance (gm) of the transistor in sub-threshold region, linear
region and saturation region respectively.
 Calculate the ratio of the transconductance (gm) and the Drain current (IDS) of the
transistor in sub-threshold region, linear region and saturation region respectively
and draw a rough curve to show the trend (gm/IDS versus IDS).
 In analog circuit design, we usually choose VGS-VTH (the overdrive voltage Vov) to
be approximately 0.2V, please note what you think the reasons are. (bonus)
Try your best to make sure your answers contain detailed deduction and precise
explanations!!!