330 Lecture 31 asic Amplifier Analysis High-Gain Amplifiers urrent Source iasing (just introduction)
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
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
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
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
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
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
an use these equations only when small signal circuit is XATLY like that shown!!
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
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?
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
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
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
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
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
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
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
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
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
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
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!
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
nd of Lecture 33