## 这是一篇来自澳洲的模拟电路作业代写

The take home midterm contains one problem with four parts. Each part has been labelled with P, C, D or HD that indicates the level of difficulty. P means that the question could be attempted by all students and students who answer the question correctly are at the level of “pass”. C means the question could be attempted by students who are at the level of “credit” in the course. D and HD indicate the question could be attempted by students who are at the level of “Distinction” and “High Distinction”, respectively.

A three-stage transistor amplifier is shown in Fig. 1. It consists of one n-channel MOSFET transistor M1 in depletion mode with W/L = 1 and two BJT transistors Q1 and Q2. The transistors have the model parameters as provided in the table below.

**PART I (Amplifiers configuration) **

a) [P] Identify the amplifier configuration used in each stage of the amplifier. [3 marks]

b) [P,C] what are the functions of C1, C2, C4, and C6 capacitors? [4 marks]

c) [P,C] Explain what are the purposes of each amplifier, and can a single-stage transistor (say stage 1 or 2 or 3) be used instead? [Hint: what are the requirements of voltage amplifiers in terms of input and output resistance? [3 marks]

**PART II (Q-point and transistor model parameter calculations) **

a) [P] Draw the DC equivalent circuit of the transistor amplifier in Fig. 1. Note that capacitors act as open circuit in DC conditions. [5 marks]

b) [P,C] Show that the Q-Point values are: M1( ID=5mA, VDS=2.1V), Q1 (IC=1.57mA,VCE = 4.93V), and Q2 (IC=1.99mA,VCE= 8.36V). [6 marks]

c) [P,C] Calculate the transistor model parameters for each transistor, namely gm1, gm2,gm3, ro1, r02, ro3, rπ2 and rπ3. [9 marks]

d) [D] *Comment on the possible range of resistance values that may replace the RC2 =4.81kΩ , RD1 = 2.375kΩ in the amplifier. [Hint: BJT must operate in a forward-active region and MOSFET must operate in a saturation region.]

[10 marks]

**PART III (Calculating mid-band gain, input, and output resistance) **

a) [P,C] Draw a small-signal equivalent circuit of the amplifier in the form suitable for mid-frequency. [5 Marks]

b) [P,C,DN] *Calculate the mid-band voltage gain of the amplifier, input resistance and output resistance. [15 Marks]

c) [HD] **Calculate the mid-band current and power gain. [10 Marks]

**PART IV (Calculating bandwidth) **

a) [P,C] Draw small-signal equivalent circuit of the amplifier in the form suitable for low frequency. [5 marks]

b) [P,C] Calculate the lower 3dB frequency, fL, of the amplifier using the appropriate time constant method. [10 marks]

c) [P,C] Draw small-signal equivalent circuit of the amplifier in the form suitable for high frequency analysis. [5 marks]

d) [DN]*Calculate the higher 3dB frequency, fH, of the amplifier using the appropriate time constant method. [10 marks]

**PART V (LTSpice or Pspice Simulation) **

a) [DN] *Simulate Fig. 1 and compare the results with your calculation in part I-IV. The Spice transistor models will be uploaded on Moodle. [10 marks]