EE 105 - Fall 2009 - Salahuddin - Midterm 3 (solution)

EE 105 - Fall 2009 - Salahuddin - Midterm 3 (solution) -...

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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 cut-off frequency? Find out the expression for cut-off frequency for the following circuit in terms of MOSFET capacitances and gm. VDD Vino—I M1 Vout RL ()1, CUiOFF 'B’vqu'w’igfl is dH-m‘nwi as Hie fiquéxnwgl ;. => 'gmzeni: a, I VU’ULE Z‘ 2 V‘ , 0 Hfll : m ’0 CW” figs levfievi “’3‘” i/cjm FL 3/ i - {Eff VU‘LLL R'— 1fl- Vr‘fl : lF ngJrEL _ V91?! 1 l ' l/gmAFizL Mama gm timing” 1 WW 2 L Z0” . :2 ’itlflfl'i‘ i‘i‘gmflL} { 1. MOSFET: Principie of Operation [16 pts] (3) [2 pts]Draw a schematic of a MOSFET with p-type 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 * ~ ~; 1a; aLiLiu/VECG, CL 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 p-type 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. QiLfi-Lxrpctww 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 + P-subsimte 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 Id-Vd 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: muse-Arse bm‘iWLL. lit/M V“? gets iii-P- 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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EE 105 - Fall 2009 - Salahuddin - Midterm 3 (solution) -...

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