“In the name of God”
Tutorial of ECE 340 Course
Instructor: Professor Karim
Seyyed Mojtaba Pourjaafari
Winter 2020
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4.1 Figure 1 shows a discrete-circuit amplifier. The input signal 𝑣𝑠𝑖𝑔 is coupled to the gate through a very large capacitor (shown as infinite). The transistor source is connected to ground at signal frequencies via a
very large capacitor (shown as infinite). The output voltage signal that develops at the drain is coupled to a load resistance via a very large capacitor (shown as infinite). All capacitors behave as short circuits for signals and as open circuits for dc.
(a) If the transistor has 𝑉 = 1𝑉, and 𝑘 = 4 𝑚𝐴/𝑉2, verify that the bias circuit establishes 𝑉 = 𝑡𝑛 𝐺𝑆
1.5 𝑉, 𝐼 = 0.5𝑚𝐴, and 𝑉 = +7 𝑉. That is, assume these values, and verify that they are consistent with 𝐷𝐷
the values of the circuit components and the device parameters. (b)Find𝑔 and𝑟 if𝑉 =100𝑉.
𝑚𝑜𝐴
(c) Draw a complete small-signal equivalent circuit for the amplifier, assuming all capacitors behave as short circuits at signal frequencies.
(d)Find𝑅𝑖𝑛, 𝑣𝑔𝑠 , 𝑣𝑜 ,𝑎𝑛𝑑 𝑣𝑜 . 𝑣𝑠𝑖𝑔 𝑣𝑔𝑠 𝑣𝑠𝑖𝑔
Figure 1
4.2 The NMOS transistor in the CS amplifier shown in Figure 2 has 𝑉 = 0.7 𝑉 and 𝑉 = 50 𝑉. 𝑡𝐴
(a) Neglecting the Early effect, verify that the MOSFET is operating in saturation with 𝐼𝐷 = 0.5 𝑚𝐴 and 𝑉 = 0.3 𝑉. What must the MOSFET’s 𝑘 be? What is the dc voltage at the drain?
𝑂𝑉 𝑛 (b) Find 𝑅𝑖𝑛 and 𝐺𝑣.
(c) If 𝑣 is a sinusoid with a peak amplitude 𝑣̂ , find the maximum allowable value of 𝑣̂ for which 𝑠𝑖𝑔 𝑠𝑖𝑔 𝑠𝑖𝑔
the transistor remains in saturation. What is the corresponding amplitude of the output voltage?
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Figure 2
4.3 The MOSFET in the circuit of Figure 3 has 𝑉 = 0.8𝑉 , 𝑘 = 5 𝑚𝐴 𝑎𝑛𝑑 𝑉 = 40 𝑉. 𝑡 𝑛 𝑉2 𝐴
(a) Find the values of 𝑅𝑠 , 𝑅𝐷 𝑎𝑛𝑑 𝑅𝐺 so that 𝐼𝐷 = 0.4 𝑚𝐴, the largest possible value for 𝑅𝐷 is used while a maximum signal swing at the drain of ±0.8 𝑉 is possible, and the input resistance at the gate is 10 𝑀Ω.
(b) Find the values of 𝑔 and 𝑟 at the bias point. 𝑚𝑜
(c) If terminal Z is grounded, terminal X is connected to a signal source having a resistance of 1 𝑀Ω, and terminal Y is connected to a load resistance of 10 𝑘Ω, find the voltage gain from signal source to load.
(d) If terminal Y is grounded, find the voltage gain from X to Z with Z open-circuited. What is the output resistance of the source follower?
(e) if terminal X is grounded and terminal Z is connected to a current source delivering a signal current of 50 𝜇𝐴 and having a resistance of 100 𝑘Ω, find the voltage signal that can be measured at Y.
Figure 3
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