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Unformatted text preview: UNIVERSITY OF CALIFORNIA, BERKELEY
College of Engineering
Department of Electrical Engineering and Computer Sciences
BB 105: Microelectronic Devices and Circuits Fall 2009 MIDTERM EXAMINATION #3 11/24/2009
Time allotted: 75 minutes
, “\
NAME: L'L'hm
STUDENT ID#:
INSTRUCTIONS: 1. SHOW YOUR WORK. (Make your methods clear to the grader!)
2. Clearly mark (underline or box) your answers.
3. Specify the units on answers whenever appropriate. SCORE:1 /16
2 /18
3 /16 Total / 50 (d) [5 pt] What is the definition of cutoff frequency? Find out the expression for cutoff frequency for
the following circuit in terms of MOSFET capacitances and gm. VDD Vino—I M1 Vout
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{ 1. MOSFET: Principie of Operation [16 pts]
(3) [2 pts]Draw a schematic of a MOSFET with ptype substrate clearly showing the type of
doping in source, drain and gate poly region. e 3 WW I b _ m (b) [2 pts] Draw the equivalent capacitive network cleariy mentioning H1ephysical origin of each
of the capacitances. . ' ‘ t [a +CY
x \ . ,_ L“: HID MAJ
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6'01 tax L P o (LC/LP 61 (LC 4. 017M“ C V24. .1. Cowp Cdmo: déplﬁﬁon 'ihé [34/le (c) [4 pts] Draw the CV characteristic of a MOSFET with ptype substrate. Explain the different
regions using the capacitance network from part (b). ‘ . ' '— (Loo
01 s 7 S MYTH. .L (d0? Ldbp ‘ H 4
Cd“? (5' :: H ELLE?
. Celt + 50L“? I 
(d) [8 pts]
(i) [2 pts] Write down the equation of drain current as a function of gate and drain voltages in the linear and saturation region. QiLﬁLxrpctww I (iilltl pts} Draw Id vs. Vd for the long channel MOSFET shown in the figure for the specified biasing
conditions. Note that all the voltages are measured with respect to ground which is at zero voltage. In
your plot, you must specify numerical values of all the relevant voltages. The current values need not be calculated numerically. Assume Vg=1 V. A .
ssume Mzow C 01 VFR + 2¢E + Psubsimte l vats > Vas  Yul
Vsubstrate=0.2V . . , V9 h V‘U'c V9 :—l V; Va 1 Ci' 3 V (iiil{2 pt] Show qualitatively how the IdVd will change ifthe substrate voltage is modified in the
following way? Assume Vg:1 V. n ‘ ’.. ﬂ so are t :3 1,in chem LS ‘ r (IQ:
museArse bm‘iWLL. lit/M V“? gets iiiP Usubstrate=D.4 V 2. [18 pt] Operation of MOSFET and basic amplifiers. (a) [2 pt} Considering that Idm <1 L 1M, explain why channel length modulation does not
ff h I . . '
a ectt e ong channel MOSFETs I . LP (X. J— I—f 4L
dsext “ km, L “C
A L 
T << L (b) [2 pt] The equatiOn for current including channel length modulation is usually expressed as: 10,301 =_/‘ C *0/05 _V’IH)1[I+)"(VDS _VD‘:aI] What relationship between A and (VDyVD,,a‘) is assumed to derive this equation? 43L x (we. ism) (c) [2 pt] Draw the small signal equivalent of a CS ampliﬁer with )L a: 0. (d) [4 pt] Consider the following circuit where two short channel MOSFETs of equal length have
been arranged to give an ampliﬁer. Approximate the total gain of this amplifier. Provide a
numerical value. (e) [6 pt] For the circuit shown below find out (2 : O.) A 81
m ,8 = *0
51]
(ii) Small signal input impedance.
(iii) Small signal voltage gain‘ Pin : L W" a :_ L
1 7C VF} + {2* 3. [16 pt] MOSFET Cascodes, Current mirrors and Frequency Response.
(2:) [3 pt] What is the output impedance of the following stage? (b) [3 pt] Draw all the capacitances (relevant to the small signal response) of a MOSFET clearly
identifying their physical origins. CM b
C (gal : (c) 15 pt]lf M1 and M; are identical transistors, which of the following will operate at a higher
frequency than the other? Show by comparing each one's pole frequencies. (a) (b)
VDD
I/DD RD
R vout
D Vb"— M2
,0 Vout Y
Van —WV"I II/l1 Vin<> R M1
RG ___ G =
f M mm 4 e9” 6910+ mm) {L a;
\AeLl 2/ gm. g m 2
mul : ‘Jm i3)»
b ...
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