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Summer 2009 Midterm

This document is a midterm exam for the EECE 311 course at the American University of Beirut, focusing on electronic circuits. It includes a series of questions related to MOSFET circuits, requiring calculations of DC drain currents, voltage gains, input/output resistances, and frequency responses. The exam is open book and consists of 20 questions, each worth 2 points.

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13 views2 pages

Summer 2009 Midterm

This document is a midterm exam for the EECE 311 course at the American University of Beirut, focusing on electronic circuits. It includes a series of questions related to MOSFET circuits, requiring calculations of DC drain currents, voltage gains, input/output resistances, and frequency responses. The exam is open book and consists of 20 questions, each worth 2 points.

Uploaded by

jbeilyelio
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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American University of Beirut

Department of Electrical and Computer Engineering


EECE 311 – Electronic Circuits
Summer 2009
Midterm – July 20, 2009
Open Book – 75 minutes _ GRADE: / 40

NAME:___________________________ ID Number: ______________________

All questions are 2 points each.

In the circuit shown below, VDD = 3 V and the two MOSFETs are identical and
matched with W = 10 μm, L = 0.2 μm, Vt = 0.5 V, and k’n = 200 μA/V2. Neglect
body effect and assume λ = 0.

The input vIN is a small sinusoidal signal superimposed on a DC level equal to


VBIAS = 1.5 V. The same DC VBIAS (without any signal) is also applied at the gate of
MOSFET Q2.

1) Find the DC drain currents in Q1 and Q2.

2) Find the values of VOV and gm for Q1 and Q2.

3) Find the DC voltage at node X, VX.

4) If the signal at node X is considered the output of the Q1 amplifier stage, determine
the type of this amplifier (the first stage).

5) If the signal at node X is considered the input of the Q2 amplifier stage, determine
the type of this amplifier (the second stage).

6) Find the input resistance of the amplifier Ri.


7) Find the output resistance of the amplifier, Ro.

8) Find the small-signal voltage gain of the first stage, vx/vin. Hint: Use the T model.

9) Find the small-signal voltage gain of the second stage vout/vx.

10) What is the total amplifier voltage gain vout/vin, in dB?

The capacitances in the circuit are modeled as a load capacitor CL = 25 fF that appears
between the output of the amplifier and ground, and another capacitor CX = 20 fF that
appears between node X and ground.

Using the OCTC method:

11) Find the open-circuit resistance seen by CL.

12) Find the open-circuit resistance seen by CX.

13) Find the 3-dB frequency for the amplifier.

14) Show and label the magnitude Bode plot for the amplifier assuming a single pole
at the frequency calculated in part (13).

Assume in the following that the 1 mA current source is implemented as a simple


MOSFET current mirror.

15) Show the circuit implementation for such a current mirror. Name the mirror
transistor Q3, and assume that it is identical to Q1 and Q2.

16) What is the lowest possible voltage at node X to keep Q3 saturated?

17) What is the output resistance of the current source if, for Q3, λ = 0.1 V–1?

18) If the voltage at node X changes by +0.1 V, find the change in current for the
current source.

19) The 1 kΩ resistor between the drain of Q2 and the DC supply voltage is
implemented as a MOSFET with gate connected to drain. Show how this MOSFET is
connected.

20) Find the (W/L) ratio of the MOSFET in part (19) to get an equivalent small-signal
resistance of 1 kΩ at a current level of 0.5 mA.

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