EE 435. Lecture 10: Current Mirror Op Amps

Transcription

1 EE 435 ecture 0: urrent Mirror Op mps

2 Review from last lecture: Folded ascode mplifier DD DD B3 B3 B B3 B2 B2 B3 DD DD B B B4 I T QURTER IRUIT Op mp 2

3 Review from last lecture: Folded ascode Op mp DD M 5 M 6 B M 3 M 4 B2 M 9 M 0 M M 2 M7 B3 M 8 B4 I T I T2 Needs MFB ircuit for B4 Either sinle-ended or differential outputs an connect counterpart as current mirror to eliminate MFB Foldin caused modest deterioration of 0 and GB enery efficiency Modest improvement in output swin 3

4 Review from last lecture: Folded Gain-boosted ascode mplifier o o o3 m3 - I B M 3 GB 2 M I B2 with ideal current source bias modest improvement in output swin 4

5 Review from last lecture: Basic mplifier Structure omparisons ommon Source ascode Reulated ascode Folded ascode Folded Reulated ascode Small Sinal Parameter Domain O O O O O O O m O m3 o3 m3 o3 m3 O O5 o3 O O5 m3 o3 GB m GB GB GB GB 5

6 Review from last lecture: Basic mplifier Structure omparisons ommon Source ascode Reulated ascode Θ=pct power in Folded ascode Θ=fraction of current of M 5 that is in M O O Practical Parameter Domain O O 4 λ λ 4 λ λ 3 2 λ 3 4θ EB EB EB EB3 EB3 θλ λ5 λ3eb EB3 2P GB DD 2P GB DD 2P GB DD EB EB 2P - θ GB DD θ EB EB Folded Reulated ascode Θ =pct of total power in Θ 2 =fraction of current of M 5 that is in M O 4θ θ 2λ λ5 λ3eb EB3 2 2P GB DD θ2 - θ EB 6

7 Review from last lecture: Folded Gain-boosted Telescopic ascode Op mp DD o O O5 2 o3 3 m3 o7 o9 m9 B M 5 M 6 M M 4 B2 OU T B3 GB 2 I N I N M M 2 M7 M 9 2 M M 8 B4 0 I T I T2 S S S S Needs MFB ircuit for B4 Either sinle-ended or differential outputs an connect counterpart as current mirror to eliminate MFB Foldin caused modest deterioration in GB efficiency and ain Modest improvement in output swin 7

8 Review from last lecture: Operational mplifier Structure omparison Small Sinal Parameter Domain Reference Op mp O 2 O O3 GB 2 IT SR 2 Telescopic ascode o o o3 m3 2 o7 o5 m5 GB 2 IT SR 2 Reulated ascode o o o3 m3 2 o7 o9 m9 3 GB 2 IT SR 2 Folded ascode o o o5 2 o3 m3 o7 o9 m9 GB 2 IT SR 2 Folded Reulated ascode o o o5 2 o3 m3 3 o7 o9 m9 9 GB 2 IT SR 2 8

9 Other Methods of Gain Enhancement BB Recall: DD ounterpart ircuit Quarter ircuit 0 OQ GB MQ mq Two Strateies: O. Decrease denominator of 0 2. Increase numerator of 0 Previous approaches focused on decreasin denominator onsider now increasin numerator 9

10 meq Gain Enhancement Stratey : M MQ M m is increased by the mirror ain! use the quarter circuit itself to form the op amp M I B Use this as a quarter circuit 0

11 meq Gain Enhancement Stratey : M M : : M I B I B M I B M M 2 I T

12 urrent Mirror Op mps M : : M I B I B M M 2 I T ery Simple Structure! Premise: Transconductance ain increased by mirror ain M Premise: If output conductance is small, ain can be very hih Premise: GB very ood as well Still need to enerate the bias current I B M meq 2 0 GB meq meq OEQ 2

13 urrent Mirror Op mps DD DD M : : M M 5 M 3 M 4 M 6 M M 2 IN M M 2 I T B2 I T M 9 B M 7 M 8 Need MFB t0 establish B2 Basic urrent Mirror Op mp an use hiher output impedance current mirrors an use current mirror bias to eliminate MFB but loose one output 3

14 Is this a real clever solution? 4

15 Basic urrent Mirror Op mp DD M 5 M 3 M 4 M 6 M meq 2 OEQ O6 O8 B2 IN M M 2 M 9 B I T M 7 M 8 MFB not shown O GB SR M 2 M 2 O6 MI 2 T O8 5

16 urrent-mirror Op mp offers stratey for m enhancement ery Simple Structure Has applications as an OT But how ood are the properties of the MO? Is this a real clever solution? 6

17 Seminal Work on the OT From: N.E.. PROEEDINGS 7

18 Seminal Work on the OT From: 969 N.E.. PROEEDINGS December 969 8

19 Oriinal OT I B I M I 2 I I I I 2 I B I OUT I 3 I 4 Q Q 2 I B Q 3 Q 4 urrent Mirror I I I B 4 I I I 3 OUT 3 I 4 I OUT M I B I 9

20 Oriinal OT I B I M I 2 I I MI IB MI 2 I I I 2 I B I OUT I 3 I 4 Q Q 2 I B Q 3 Q 4 I OUT M I B I 20

21 Oriinal OT I MI IB MI 2 I I I 2 I B I OUT I 3 I 4 Q Q 2 I B Q 3 Q 4 I OUT M I B I 2

22 Oriinal OT I MI IB MI 2 I I I 2 I B I OUT I 3 I 4 Q Q 2 I B Q 3 Q 4 3-mirror OT I OUT M I B I 22

23 urrent Mirror Op mp W/O MFB DD M : : M M meq Often termed an OT I T I OUT m : Introduced by Wheatley and Whitliner in 969 I OUT m IN 23

24 OT ircuits OT often used open loop Excellent Hih Frequency Performance Gain can be made prorammable with dc current are or very lare adjustment ranes possible m I OUT m K K I I B B for for BJT circuits MOS circuits I B 2 to 3 decades of adjustment for MOS 5 to 6 decades of adjustment for BJT 24

25 OT pplications m R OUT R m IN m is controllable with I B oltae ontrolled mplifier Note: Technically current-controlled, control variable not shown here and on followin slides 25

26 OT pplications m OUT R m IN R oltae ontrolled Invertin mplifier 26

27 OT pplications R IN m R IN m R IN m R IN m oltae ontrolled Resistances 27

28 OT pplications m2 m2 OUT m 2 Noninvertin oltae ontrolled mplifier in OUT m 2 Invertin oltae ontrolled mplifier in Extremely lare ain adjustment is possible oltae ontrolled Resistorless mplifiers 28

29 OT pplications m m s s m m OUT in OUT in Noninvertin oltae ontrolled Interator Invertin oltae ontrolled Interator oltae ontrolled Interators 29

30 omparison with Op mp Based Interators R R sr OUT R R sr OUT OT-based interators require less components and sinificantly less for realizin the noninvertin interation function! 30

31 Properties of OT-Based ircuits an realize arbitrarily complex functions ircuits are often simpler than what can be obtained with Op mp counterparts Inherently offer excellent hih frequency performance an be controlled with a dc voltae or current Often used open-loop rather than in a feedback confiuration (circuit properties depend directly on m ) Other hih output impedance op amps can also serve as OT inearity is limited Sinal swin may be limited but can be ood too ircuit properties process and temperature dependent 3

32 urrent-mirror Op mp offers stratey for m enhancement ery Simple Structure Has applications as an OT But how ood are the properties of the MO? Is this a real clever solution? 32

33 urrent Mirror Op mp W/O MFB DD DD M 5 M 3 M 4 M 6 M : : M M M 2 I T I T M 9 B M 7 M 8 : an use hiher output impedance current mirrors to decrease OEQ OEQ O O6 O8 meq M M O6 O8 MI SR T 33

34 SR of urrent Mirror Op mp DD DD M 5 M 3 M 4 M 6 M 5 M 3 M 4 M 6 IN M M 2 M M 2 B2 I T I T M 9 B M 7 M 8 M 9 B M 7 M 8 SR MI 2 T SR MI T 34

35 Fully Differential urrent Mirror Op mp with Improved Slew Rate DD M M : : M M I T : : Need MFB circuit and requires modest circuit modification to provide MFB insertion point 35

36 Fully Differential urrent Mirror Op mp with Improved Slew Rate This circuit was published because of the claim for improved SR (Fi 6.5 MJ) DD M 5B M 3 M 4 M 6B M 5 M 6 M M 2 I T M 9 B M 7 M 8 M 8B M 9B Need MFB circuit and requires modest circuit modification to provide MFB insertion point 36

37 Fully Differential urrent Mirror Op mp with Improved Slew Rate DD M 5B M 5 M 3 M 4 M 6 M 6B SR MI T M M 2 SR MOp mp MI 2 T M 9 B I T M 7 M 8 Improved a factor of 2! but M 8B M 9B Need MFB circuit and requires modest circuit modification to provide MFB insertion point 37

38 Fully Differential urrent Mirror Op mp with Improved Slew Rate M 5B M 8B M 5 M 9 B DD M 3 M 4 M M 2 I T M 7 M 6 M 8 M 9B M 6B MIT SR MIT SR MOp mp 2 Improved a factor of 2! but I P P SR SR M Op mp MOp mp I DD T 2 DD T M M P M 2 M DD P M 2M DD SR actually about the same for improved SR circuit and basic OT 38

39 omparison of urrent-mirror Op mps with Previous Structures Does the simple mirror ain really provide an almost free ain enhancement? DD O M 2 O6 O8 M 5 M 3 M 4 M 6 IN M M 2 M W 6 W B2 I T M 9 B M 7 M 8 39

40 Reference Op mp onsider sinle-ended output performance : (s) s 2 O O3 DD B M 3 M 4 O 2 O O3 0 λ λ 3 EB M M IN 2 IN GB 2 GB P 2 DD EB B2 I T M 9 IT SR 2 SR 2 P DD 40

41 omparison of urrent-mirror Op mps with Previous Structures Does the simple mirror ain really provide an almost free ain enhancement? I IN M 4 M 6 I OUT W 6 M W 4 M 4 6 m6 m 4 O O M 2 O6 m6 m 4 O6 O8 2 O8 Gain Enhancement Potential ess pparent but still Improved by m6 / m4 ratio 4

42 omparison of urrent-mirror Op mps with Previous Structures Does the simple mirror ain really provide an almost free ain enhancement? O M 2 O6 O8 B2 DD M 5 M 3 M 4 M 6 M 9 IN M M 2 B I T M 7 M 8 onsider how the ain appears in the practical parameter domain 0 EB 2 IT 2 M 2 λ λ I IT λ λ M6 M8 D8Q EB M6 M8 EB EB λ M6 IT M 2 λ M8 M 2 2λ This is exactly the same as was obtained for the simple differential amplifier! For a iven EB, there is NO ain enhancement! 42

43 omparison of urrent-mirror Op mps with Previous Structures How does the GB power efficiency compare with previous amplifiers? DD M : : M GB P meq M 2 MIT 2 I M DD T EB M M 2 GB MIT 2 EB 2 EB P DD M M I T GB for Telescopic ascode and Ref Op mp! GB efficiency decreased for small M!! 43

44 omparison of urrent-mirror Op mps with Previous Structures How does the SR compare with previous amplifiers? DD M : : M M M 2 I T SR P SR Re f Op mp SR DD I T P 2 DD IT 2 MI 2 SR Improved by factor of M! but M M M P SR Re f Opmp 2 DD SR Really ess than for Ref Op mp!! T 44

45 omparison of urrent-mirror Op mps with Previous Structures DD How does the urrent Mirror Op mp really compare with previous amplifiers or with reference amplifier? M : : M Perceived improvements may appear to be very sinificant M M 2 ctual performance is not as ood in almost every respect! I T 45

46 urrent-mirror Op mps nother Perspective! DD M 5 M 3 M 4 M 6 IN M M 2 B2 I T M 9 B M 7 M 8 Differential Half-ircuit

47 urrent-mirror Op mps nother Perspective! M 4 M 6 M 2 M 8 Differential Half-ircuit ascade of n-channel common source amplifier with p-channel common-source amplifier!

48 urrent-mirror Op mps nother Perspective! M 2 M 4 M 6 M O O m m m O O m m m O O m O M Differential Half-ircuit ascade of n-channel common source amplifier with p-channel common-source amplifier! From urrent Mirror nalysis :

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