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Chapter 5Passive and Active Current Mirrors

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Current Mirrors

IOUTunCox

2

W

L( R2

R2 + R1VDD VTH)

2

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Reference Currents

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Amplifier Bias Example

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Cascode Current Mirror

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Cascode Current Mirror (cont.)

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Cascode Current Mirror (cont.)

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Cascode Current Mirror Biasing

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Active Current Mirror

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Open Loop Constraints

C i h h G ill C i

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Small-Signal Current Mirror

Av GmRout

C i h Th M G Hill C i I

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Calculation of Gm

ID1 = ID3 = ID4 =gm1,2Vin/ 2 ID2 = gm1,2Vin/ 2

Iout =ID2 ID4 = gm1,2Vin ,Gm = gm1, 2

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Calculation of Rout

IX =2 VX

2ro1, 2 +1/gm3+ VX

ro4

Rout ro2 || ro4 , (2ro1,2 >> [1/gm3] || ro3 )

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Small-Signal Gain

Av gm1,2 (ro2 || ro4 )

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Common Mode Characteristics

ACM= Vout

Vin,CM

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Common Mode (cont.)

ACM

1

2gm3,4||ro3,4

21

2gm1,2+RSS

= 11 + 2gm1,2RSS

gm1,2

gm3, 4

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Common Mode (cont.)

CMRR =ADM

ACM

= gm1, 2(ro1,2|| ro3,4 )gm3,4 (1 + 2gm1,2RSS)

gm1,2

= gm3,4 (ro1, 2|| ro3,4 )(1 + 2gm1, 2RSS)