Question

Q6. An amplifier circuit using an n-MOSFET is shown in Fig. Q6. The n-MOSFET has the following parameters: K'-1 mA/V2 and λ-0.02 w. v°' is a small signal AC voltage ource 8V 8V Vout Ra 2.56 mA Fig. Q6 (a) Calculate the DC gate voltage, Va. (b) Assuming that the n-MOSFET is operating in the saturation region and neglecting channel length modulation, calculate the threshold voltage, VrHN, given that the voltage drop across the de current sorce, Inas, has been designed to be approximately 0 V. Verify that the n-MOSFET is operating in the saturation region. (c) Find the values of small signal parameters gm and ro of the n-MOSFET (d) What is the configuration of the amplifier circuit? (e) Draw the small signal ac equivalent circuit of Fig. Q6. You may assume that in the small signal ac equivalent circuit, all the coupling capacitors behave like short circuuts. (f) Calculate the input resistance, Rn, and output resistance, Row. (3) Calculate the voltage gain,

Answer 1

D C Equivalent circuit given amplifier circuit show below capacitor rightarrow open circuit a c voltage source - short circuit (a) Refer to fig v_G = 8 times R_L/R_1 + R_2 = 8 times 30 k/70 k + 30 k = 240/100 = 2.4 V v_G = 2.4 volts (b) Drain current I_D = k_n (v_GS - v_T mu N)^2 (1) since I_D = I_B mu s = 2.5 m A and voltage across I_B I N given as 0 v therefore V_GS = V_G = 2.4 V Rightarrow From (1) 2.56 times 10^- 3 = 1 times 10^- 3 (2.4 - V_T mu N)^2 Rightarrow V_T mu N = 0.8 V Refer to fig 1 K V L at output loop Rightarrow 8 - I_D R_D - v_DS + 0 V = 0 V_DS = 8 - 2.56 times 10^- 3 times 2 times 10^3 = 2.88 V v_bs (sat) = v_(0) - v_T H mu = 2.4 - 0.8 = 1.6 volts Since v_DS > v_DS (sat) Rightarrow n - MWFET operating in SATURATION REGION \r\n