ECE 3110: Engineering Electronics II
Fall 2008
Assignment #1
Topics: Units, Amplifiers, MOSFETs
Due Date: Sept. 5, 2008
Problem 1: (Section 1.4) Measured input voltages and currents, output voltages,
and load resistances are specified below for two different amplifiers. For each
case, calculate the voltage gain (Av ), current gain (Ai ), and power gain (Ap ).
The measurements are for sinusoidal signals, and are specified as either rms or
peak-to-peak values. Provide answers in both linear units and dB.
(a) vI,rms = 100 mV, iI,rms = 100µA, vO,rms = 10 V, RL = 100Ω [Av = 1E2 =
40dB, Ai = 1E3 = 60dB, Ap = 1E5 = 50dB ]
(b) vI,pp = 10µV, iI,pp = 100 nA, vO,pp = 2 V, RL = 10 kΩ [Av = 2E5 =
106dB, Ai = 2E3 = 66dB, Ap = 4E8 = 86dB ]
Problem 2: (Section 1.4.8) A non-linear amplifier has a transfer function vOU T =
3
, and an input of vIN = 2 + 0.01 sin(ωt).
vIN
(a) Find the maximum and minimum values of the output voltage using a
small signal approximation. [vOU T,max = 8.12 V, vOU T,min = 7.88 V ]
(b) Find the maximum and minimum values of the output voltage using the
exact equation. [vOU T,max = 8.1206 V, vOU T,min = 7.8806 V ]
Problem 3: (Section 1.5) An amplifier has 40 dB of small-signal open-circuit voltage gain, an input resistance of 1 MΩ, and an output resistance of 10 Ω. Assume
that a 100 Ω load resistance has been connected to the output.
(a) Find the voltage and power gain (expressed in dB) for this configuration.
[Av = 39.2dB, Ap = 79.2dB ]
(b) If the amplifier has a peak output current of 100 mA, what is the maximum
allowable input sine-wave (expressed in rms) for which no clipping will
occur? [78 mV rms]
(c) How much power is dissipated in the load resistance under these conditions?
[0.5 W ]
Problem 4: (Section 2.2) An ideal op amp is connected as shown in Fig. 2.5 of the
text, with R1 = 10 kΩ and R2 = 100 kΩ. A square wave is applied to the input
with levels of 0 V and 1 V. Sketch the output waveform, labeling the maximum
and minimum values. [vOU T,max = 0 V, vOU T,min = -10 V ]
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ECE 3110: Engineering Electronics II
Fall 2008
0
Problem 5: (Section 4.2) An NMOS transistor with Vt = 1 V and kN
(W/L) = 0.1
2
mA/V needs to be biased for operation in the saturation region with iD = 0.2
mA.
(a) What should vGS be set as? [3 V ]
(b) What is the minimum allowable vDS ? [2 V ]
Problem 6: (Section 4.3) Sedra and Smith: Chapter 4, problem 4.41 [W/L = 50,
R = 4.95 kΩ]
Problem 7: (Section 4.6) Consider an NMOS transistor with kn0 (W/L) = 2 mA/V2
and Vt = 1 V. The transistor is biased with VGS = 2 V, and VDS is set so that
the transistor remains in saturation.
(a) What is the dc bias current, ID ? [1 mA]
(b) If VGS is increased to 2.1 V, calculate the corresponding increment in ID .
[0.21 mA]
(c) Repeat (b) for VGS being decreased to 1.9 V. [-0.19 mA]
(d) Using the results of (b) and (c), calculate an estimate for gm of this transistor (remember that gm = ∆iD /∆vGS ). [2 mA/V ]
(e) Calculate gm using equation (4.62) in the text, and compare the result to
your estimate from (d). [2 mA/V ]
Problem 8: (Section 4.7) Consider the common source amplifier shown in Fig.
4.43(a) in the text, with CC1 = CC2 = CS = ∞, Rsig = 500 kΩ, RG = 10 MΩ,
RD = 10 kΩ, and RL = 20 kΩ. The transistor is biased so that gm = 2 mA/V,
and ro = 50 kΩ. Find the voltage gain from vsig to vo . [-11.2 V/V ]
Problem 9: (Section 4.7) Consider the common drain amplifier shown in Fig.
4.46(a) in the text, with CC1 = CC2 = ∞ and RG = 10 MΩ. The transistor is
biased so that gm = 5 mA/V and ro = 20 kΩ.
(a) Assuming that Rsig = 0 and RL = ∞, calculate the voltage gain from vsig
to vo . [0.99 V/V ]
(b) Repeat (a), but this time assume that Rsig = 500 kΩ and RL = 20 kΩ.
[0.934 V/V ]
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