Question

EE2027 / TEE2027 Electronic Circuits / Page 5 Q.3 A p-channel MOSFET (P-MOSFET) has the following parameters: up Cox = 2 x 10 A/V, WIL = 20, VrH=-1 V, and 2 = 0.008 V-!. The source and the body of the p-MOSFET are shorted together. The device is operating at Vso = 4 V. (a) If VSD = 2 V, which region is the p-MOSFET operating in? Calculate the drain current. (3 marks) (b) If V sp=5 V, which region is the p-MOSFET operating in? Calculate the drain current. State any assumption made in your calculation. (3 marks) (c) For operation under Vsp=5 V, estimate the small-signal model parameter values: gm, ro, and gmb. Explain your answer for gmb- (4 marks)

Answer 1

Given P-channel MOSFET lep Cox = 2x 10-3 Alva w = 20 VTH = -1V = 0.008 - VSG = 4V (a) VSD =2v VSG > INTHI => 4>HI 43 I True VSD I VSG-LVTA! 2< 4-1-11 True 2 S 3. According to the conditione VSG > THI & VSD < VSG - NTHI

P-MOSFET is operating in linear region. . Drain current IDs = lip con he [Cusg - Wel) uso - Vs] C + 2 %) $=(220*400(18-10) )- 03"}](1+000601) Sos = (2x10 5) 620) (6-4) (4- 1)] 01.016) IDs = 40x105 [6-2] (1.016) Ios = 40x165 [4] (1.016) 40 6 - IDs = 1.6256 x 10 3 A . IDS = 1.6256 mA

b) USD = 5v VSG - INTH - 43 lll 421 True NSD > VSG - lvl 57 4-1-11 53. True u According to the conditione VSG = (THI, uso isa lut The P-MOSFET is operating in saturation region. : Drain current Is- lap cox he [usa - l"Al) ² CH AUSD) IDs = (2x10-5 (20) (4-1-11)² (+0.008 (5) Jos = 20 x 10 (382 (1.04) Ins - 187 2X10-9A

lps = 1.872 MA IDs = 1.872 mA) (e) At USD=50 » ID - 1-872 mA Tran conductance: Im= 2.ID vas-VFH 2 (1,872 4- (-1) Im = 7.488x10 + v. Output resistance No= HANDS It ^ VDS 1 +0.008) (5) ro- 510 (0.008) (1:8728103 1.04 1.4976810 - 69 4 4 4 444 n

ar = -(-9mn) = 9mn 19mb = (7.488 x 10 ) where parameter = back-gate trans conductance ranges between o<n<3 depending on in'. 9 mb value varies
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