ES 330 Electronics II Homework 04 (Fall 2017 Due Wednesday, September 27, 2017)

Transcription

1 Pae1 Nae Solutons ES 330 Electroncs II Hoework 04 (Fall 2017 Due Wednesday, Septeer 27, 2017) Prole 1 onsder the FET aplfer of F for the case of t =0.4, kn = 5 A/ 2, GS =0.6, DD = 1.8 and RD = 10 k. [Assue nfnte output resstance r0.] (a) Fnd the D quanttes ID and DS ID kn GS t A and I R 1.8 (0.1) volt DS D D () alculate the value of at ths as pont. k A/ n GS t or you can use 2ID 2(0.1) 1.0 A/ 0.2 GS t

2 Pae2 (c) alculate the voltae an. The voltae an A R D Prole 2 A polar transstor wth current an = 100 s ased to operate at a D collector current of 0.5 A. Fnd the values of transconductance, and resstances r and re. Usn I = 0.5 A, Transconductance I 0.5 A 20 A/ = 0.02 A/ Base nput resstance r A/ Etter juncton resstance re A/ Repeat ths exercse for a collector current of 50 croaperes. Usn I Transconductance = 0.05 A = 50 μa, I 0.05 A 2.0 A/ = A/ Base nput resstance r 50, A/ Etter juncton resstance re A/ Prole 3 A desner wants to desn a polar aplfer wth a transconductance of 30 A/ and a ase nput resstance of 3000 ohs or reater. What collector as current I should the desner choose? What s the nu value of current an that can e tolerated?

3 Pae3 30 A/ and r 3,000 ; What s the nu β allowed? I I and r ; Hence, r β I I B B A I I 30 A I 0.75 A r β (303000) β; so the nu β s 90 or β 90 s the requreent for paraeter β Prole 4 For the conceptual crcut shown elow (ths s an A crcut t nores the D asn), let R = 2 k, = 50 A/ and current an = 100. If a peak-to-peak output voltae of 1 volt s easured at the collector node, what are the peak-to-peak values of the ase-etter voltae ve and ase current? We know R 2000, 50 A/, and β r β, thus, r The voltae an s A R (0.05)(2000) 100 Next, we are told that the output voltae v ax n At the output node, we have vout, pkpk vce vce 1 volt 0 swn s peak-to-peak 1 volt.

4 Pae4 For the output node, then v v v 1 volt ax n out, pkpk ce ce Thus, wth a voltae an A of -100, the ase voltae swn s v v 1 v volt = v v v 0.01 volt ax n ce ce ax n nput nput, pkpk e e e, pkpk A 100 v nput e, pkpk 0.01 And, pkpk s ven y, pkpk = A r 2000 Prole 5 Etter Follower Stae The crcut scheatc shown elow s an aplfer confuaraton known as an Etter follower. The scheatc ots the D asn detals of ths stae. The polar transstor s a coon-collector confuraton. Replace the polar transstor wth ts sall-snal T equvalent crcut odel and show that the sall-snal A nput resstance s rn Rn ( 1)( re Re ). Show that the rato of output voltae to nput voltae can e expressed as v R o e Re r

5 Pae5 Soluton: On the next pae we show the T-equvalent crcut susttuted for the transstor syol n the Etter Follower stae. v r n v 0 R e v r e E R e v 0 The nput resstance of the entre stae s found y coputn the rato of the appled nput voltae (v ) dded y the ase current. rn where ( 1) re ( 1) Re ; re and Re are n seres. ( 1) re ( 1) Re rn ( 1)( re Re ) The output voltae v I R and I ( 1) ; v ( 1) R Therefore, 0 e e e 0 e v0 ( 1) Re Re v ( 1) ( r R ) ( r R ) e e e e