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3-Handouts_Handout_5b

# 3-Handouts_Handout_5b - Bipolar Differential Amplifiers...

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Bipolar Differential Amplifiers: Qualitative Analysis Different modes of operation of the BJT differential pair: (a) The differential pair with a common-mode input signal v CM . (b) The differential pair with a “large” differential input signal. (c) The differential pair with a large differential input signal of polarity opposite to that in (b). (d) The differential pair with a small differential input signal v i . Note that we have assumed the bias current source I to be ideal (i.e., it has an infinite output resistance) and thus I remains constant with the change in v CM . Common Mode Differential Mode

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Bipolar Differential Amplifiers: Large Signal Analysis 12 () / / / 1 2 The exponential relationship applied to each of the two transistors may be written as: and These two equations can be combined to obta in w hic BET B ET BB T vvV SS EE vv V E E II ie i e i αα −− == = 21 1 / / 1 ( 2 11 1 h can be manipulated to yield and From the circuit we have Which may be used to obtain the following expressions for and B BT E v ii e e I i e i I i ++ += = + 2 )/ ( 1 and and may be obtained by multiplying and by which is almost unity and plotted as shown in the fi gure E vV v CC I i e α = +
Bipolar Differential Amplifiers: Linearization For Your Information The transfer characteristics of the BJT differential pair (a) can be linearized (b) (i.e., the linear range of operation can be extended) by including resistances in the emitters. What is the role of the degeneration resistance (R e )?

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Bipolar Differential Amplifiers: DC Analysis (Example 1) ± Problem: Find the Q-points of transistors in the shown differential amplifier. ± Given data: V CC =V EE =15 V, R =R C =75k Ω , β =100 ± Analysis: A 3 . 95 ) 3 10 2(75 V 7 . 0 15 μ = Ω × = = EE 2R BE V EE V E I 100 94.4 A 101 II I C α == = 0.944 A I C I B = 15 7.92V 7.92V-(-0.7V) 8.62V VI
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3-Handouts_Handout_5b - Bipolar Differential Amplifiers...

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