L11Part2 CMRR_1

L11Part2 CMRR_1 - CMRR Zubair Rehman Figure 7.12 The basic...

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CMRR Zubair Rehman
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2 Figure 7.12 The basic BJT differential-pair configuration
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3 V B1 = V cm + 1 / 2 V d V B2 = V cm - 1 / 2 V d V cm = 1V sin[2 π *60*t] 1V @ 60 Hz V d = 10mV sin[2 π *1000*t] 10mV @ 1 kHz V o = v C1 - v C2 V o = A d V d + A cm V cm A d = -g m R C R C1 = R C2 A cm = ( α 1 R C1 - α 2 R C2 ) / 2R R = Output Resistance of dc Current Source Parameter Values Current Source I = 2mA R = 50 k Nominal R C = 10 k Nominal β = 100 I C1 = I C2 = I / 2 = 2 mA / 2 = 1 mA g m1 = g m2 = I C / V T = 1 mA / 25 mV = 40 mS A d = -g m R C = -40 mS * 10 k = -400
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4 Differential Mode Output = A d V d A d V d = -400 * 10 mV sin[ * 1000t] A d V d = -4000 mV sin[ * 1000t] A d V d = -4V sin[ * 1000t] Common-Mode Output: Case 1 β 1 = β 2 = 100 R C differ by 2% A cm = - ( α 1 R C1 - α 2 R C2 ) / 2R α 1 = β 1 / (β 1 +129 = 100 / (100 + 129 = 0.99 = α α 2 = β 2 / (β 2 +129 = 100 / (100 + 129 = 0.99 = α A cm = - α (R C1 - R C2 ) / 2R ≈ - R C / 2R
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L11Part2 CMRR_1 - CMRR Zubair Rehman Figure 7.12 The basic...

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