EE 330 Lecture 31. Basic Amplifier Analysis High-Gain Amplifiers Current Source Biasing (just introduction)

Transcription

1 330 Lecture 31 asic Amplifier Analysis High-Gain Amplifiers urrent Source iasing (just introduction)

2 eview from Last Time ommon mitter onfiguration ommon mitter onsider the following application (this is also a two-port model for this application) g << g 0 A V g m out = r in = 1 g + g π 0 g << g 0 A V out g << g 0 g << g 0 I = I β V in Q t Q V t V Input impedance is mid-range Voltage Gain is Large and Inverting Output impedance is mid-range Widely used as a voltage amplifier

3 eview from Last Time ommon ollector onfiguration For this application V OUT (this is not a two-port model for this application) V IN ommon ollector A V Small signal parameter domain = gπ + gm g + g + g + g m 0 if g >> g m Q I >> V Q t 1 A V 1 π IQ +Vt I V SS Operating point and model parameter domain g >> g o r +β in π in I >> V Q t β 0 1+g m g>> 1 m 1 g m I >> V Q t Output impedance is low A V0 is positive and near 1 Input impedance is very large Widely used as a buffer Not completely unilateral but output-input transconductance is small 0 V I t Q

4 eview from Last Time ommon ase Application V OUT (this is not a two-port model for this application) V IN V ommon ase A V gm in <<r 0 out 1 g m A V in I Q Vt Vt I Q <<r 0 out Output impedance is mid-range A V0 is large and positive (equal in mag to that to ) Input impedance is very low Not completely unilateral but output-input transconductance is small

5 ommon mitter with mitter esistor onfiguration V be g π gm V be g O V V y KL at two non-grounded nodes ( ) ( - ) V g + g + V V g = g V out 0 in m 0 ( ) ( ) V V V V V g + g0 + gπ in- gm = g0 out + gπ in V -g g +g g A V= = - V g g +g g +g +g +g g +g out m 0 π ( ) ( ) in m 0 π 0 π

6 ommon mitter with mitter esistor onfiguration V be g π gm V be g O V V A V - It can also be shown that r +β in π out

7 ommon mitter with mitter esistor onfiguration A V - r +β in π out V (this is not a two-port model) Analysis would simplify if g 0 were set to 0 in model Gain can be accurately controlled with resistor ratios Useful for reasonably accurate low gains Input impedance is high

8

9 an use these equations only when small signal circuit is XATLY like that shown!!

10 asic Amplifier Structures 1. ommon mitter/ommon Source 2. ommon ollector/ommon Drain 3. ommon ase/ommon Gate 4. ommon mitter with / ommon Source with S 5. ascode (actually : or S:D cascade) 6. Darlington (special : or S:S cascade) The first 4 are most popular

11 Why are we focusing on these basic circuits? 1. So that we can develop analytical skills 2. So that we can design a circuit 3. So that we can get the insight needed to design a circuit Which is the most important?

12 Why are we focusing on these basic circuits? 1. So that we can develop analytical skills 2. So that we can design a circuit 3. So that we can get the insight needed to design a circuit Which is the most important? 1. So that we can get the insight needed to design a circuit 2. So that we can design a circuit 3. So that we can develop analytical skills

13 Properties/Use of asic Amplifiers and S V D G D S V V SS More practical biasing circuits usually used or D may (or may not) be load

14 Properties/Use of asic Amplifiers and S V G D S V V SS Large inverting gain Moderate input impedance for JT (high for MOS) Moderate output impedance Most widely used amplifier structure

15 Properties/Use of asic Amplifiers and D (emitter follower or source follower) V G D S S V V SS More practical biasing circuits usually used or S may (or may not) be load

16 Properties/Use of asic Amplifiers and D (emitter follower or source follower) V G D S S V V SS Gain very close to +1 (little less) High input impedance for JT (high for MOS) Low output impedance Widely used as a buffer

17 and G Properties/Use of asic Amplifiers V D G D V V GG S More practical biasing circuits usually used or D may (or may not) be load

18 and G Properties/Use of asic Amplifiers V D G D V V GG S Large noninverting gain Low input impedance Moderate (or high) output impedance Used more as current amplifier or, in conjunction with D/S to form two-stage cascode

19 w or SwS Properties/Use of asic Amplifiers V D G D S S V V SS More practical biasing circuits usually used or D may (or may not) be load

20 Properties/Use of asic Amplifiers w or SwS V D G D S S V V SS easonably accurate but somewhat small gain (resistor ratio) High input impedance Moderate output impedance Used when more accurate gain is required

21 asic Amplifier haracteristics Summary /S V Large noninverting gain Low input impedance Moderate (or high) output impedance Used more as current amplifier or, in conjunction with D/S to form two-stage cascode /D V SS Gain very close to +1 (little less) High input impedance for JT (high for MOS) Low output impedance Widely used as a buffer /G V Large noninverting gain Low input impedance Moderate (or high) output impedance Used more as current amplifier or, in conjunction with D/S to form two-stage cascode w/ SwS easonably accurate but somewhat small gain (resistor ratio) High input impedance Moderate output impedance Used when more accurate gain is required V

22 epeat from earlier discussions on amplifiers ascaded Amplifier Analysis and Operation (applicable when all stages are unilateral) S ox1 V 1 ix1 A v01 V 1 V 2 L1 A v02v3 V ix2 3 ox2 V 4 L Vout ix1 L1//iX2 L AV = = AV01 AV02 Vin ix1+s L1// ix2+0x1 L+0X2 Accounts for all loading between stages!

23 ascaded Amplifier Analysis and Operation (when stages are not unilateral) Standard two-port cascade S V 11 in1 Two-Port Model 1 Two-Port A v0v1 Model 2 o1 V 12 in2 o2 V 13 in3 Two-Port Model 3 o3 V 23 V OUT V 21 V 22 A v0r1v21 A v01v11 A v0r2v22 A v02v12 A v0r3v23 A v03v13 L Analysis quite tedious because of the reverse-gain elements ight-to-left nested inx,a vx approach S V 1 inx -A VoX Model V 2 inx -A V Model V 3 inx -A V Model V 1 in1x A v1xv1 in2x A v2xv2 in3x A v3xv3 L = inx includes effects of all loading A VX s include all loading an not change any loading

24 nd of Lecture 33