Question

3. In Figure 3, the DC operating point for BJT Q, is Ici = 170 uA and VCE = 4 V, and the DC operating point for BJT 02 is Ic2 = 240 A and VCE2 = 3 V. Both Q1 and Q2 have B = 100, VA-75 V at the room temperature. Assume that all the capacitors have infinite values, and all the resistors have the values as indicated in Figure 3. (a) (b) Determine the voltage gain 4. (9 Marks) Determine the input resistance Rin and output resistance Rew of the amplifier. (6 Marks) (e) Determine the small-signal input signal range for w/ of this amplifier. (5 Marks) osv 27.2 kO IR 20.4 ks] }3 MB 500 KR 1k02 C ca u 200 kg 200k Rin La 500 k 2 SR, 1 29.2 ka 36 37.1 kn SRTC Figure 3

Answer 1

1+ .) * (1 + 8 mm) = 1+/0.10726) x (1 + 29. 25.62 29.2 1.008 N Hence Vo = 14:28 -171476 X 0115143 X 1.008 4.25tT ( CRI=lk) -107 ra 6 Hence Vollage gain, | Ar= = -107 Rona Rill R2 Il prej = Iriput Resistance Rin - 14.28k (Cakulted above) Rin = 14.28k To find Rout set Vi to o ve -

so that Ib = 0. Do. kot otvo 4. YB +D ID I-BI Rout Roll R31101 clearly BI b 2 = 0 In pre The – Q3 +D Im Roll23/1m) BIbn-] Vo = Rg Jo of Vo - Rout. = R5 Rout = 2014 kn I Rin = 14.28k Pout 2004k

Also -Brez Toy - R G D Jb2 -BI-I = 0 = -13 Tb (reat R6) + B Ib Rb +IR6 Dinde through out by Rb we get I = ß Ibz (1+rez - BIbi - ③ Toom ③ + 6 we get ß Ibz (ltrez) - Biblia - B Iba - p Thi] Rb - (R31/2) + Rb 7 .4 tot 6 pa Chor *) 7 . 7 B Ib Roll Rol L R6+ (R311) b. I. Pi tez SR 5+ R3 llaw] = p bl.

RI Jo I WoM ovo R310|| 19 YB I pter Bb. Rollkilla D) Beton 2. = -- (small signal equivalent circult.) We have Vo = -BI b 2 (Rs || Rellroa) - Apply KVL to the indicated loop as shown in I (B || D = R6 [(@+1) Ibz - I - I - 1 11 201 + Ru] Thy - p Tay] 26 - ©

For a Given B = 100, VA = 75rolt; VCE = 4 volt, Id = 17OMA. IE, = ( B+)) Ic, = (1 + ton X470 MA IE,= 176674A i emitter resistance, re, for a, is re, = 26mV - 1.5 1.434 Irel = 151,43 ~ Out put resutance rol = VA = 75 kn IE 0:17 = (do 1 = 44 1.18.ka) B = 100) VA = 75 volt, та - 240 A IE2 = 240 x (1 + tooMA (I = 24214 MAJ

- rez=26mV = 26 IE2 01 2424 - 107.2bln frez= 107,2614 in output resutance for 02, Toa= VA = 75 kn Ira 0.24 - 312.5kn pod = 312.5k) Small signal ac equiklent Circuit is shown below

oy B Jb2 = Bitby R311 input Circuit, & from the We have V = VIX Rill kill pres Bill koll på + RI But Hence Vi= pre, Ibl. w = (R: 112 11 00z) x x L x Rillkallares T4 (3(+ Pino) " Now Rull Rall Brel = 250 kl 15:143k Ž 14,286 RSRL 11202- 2014 kell a culc || 312.5t - 171476k