Lecture 22. Humming Noise in Audio Amplifier. Supply Ripple Rejection. Ripple Free Differential Output. Common Inputs to Differential Amp.

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1 4//008 Lectue OUTLNE Diffeential plifies Geneal consideations BJT diffeential pai Qualitatie analysis Lae sinal analysis Sall sinal analysis Fequency esponse Read: hapte Hu Noise udio plifie onside the aplifie below which aplifies an audio sinal fo a icophone. f the powe supply ( ) is tie ay, it will esult an additional (undesiable) oltae sinal at the output, peceied as a hu noise by the use. out R 05 Sp 008 Lectue, Slide Pof. Wu, U Bekeley 05 Sp 008 Lectue, Slide Pof. Wu, U Bekeley Supply Ripple Rejection Sce node and each see the oltae ipple, thei oltae diffeence will be fee of ipple. Ripple Fee Diffeential Output f the put sinal is to be a oltae diffeence between two nodes, an aplifie that senses a diffeential sinal is needed Sp 008 Lectue, Slide 3 Pof. Wu, U Bekeley 05 Sp 008 Lectue, Slide 4 Pof. Wu, U Bekeley oon nputs to Diffeential p. The oltae sinals applied to the put nodes of a diffeential aplifie cannot be phase; othewise, the diffeential output sinal will be zeo Diffeential nputs to Diffeential p. When the put oltae sinals ae 80 out of phase, the esultant output node oltaes ae 80 out of phase, so that thei diffeence is enhanced Sp 008 Lectue, Slide 5 Pof. Wu, U Bekeley 05 Sp 008 Lectue, Slide 6 Pof. Wu, U Bekeley 05 Fall 007

2 4//008 Diffeential Sinals Sle Ended s. Diffeential Sinals Diffeential sinals shae the sae aeae D alue and ae equal anitude but opposite phase. pai of diffeential sinals can be eneated, aon othe ways, by a tansfoe. 05 Sp 008 Lectue, Slide 7 Pof. Wu, U Bekeley 05 Sp 008 Lectue, Slide 8 Pof. Wu, U Bekeley Diffeential Pai oon Mode Response BE BE R With the addition of a tail cuent, the cicuits aboe opeate as an eleant, yet obust diffeential pai. 05 Sp 008 Lectue, Slide 9 Pof. Wu, U Bekeley 05 Sp 008 Lectue, Slide 0 Pof. Wu, U Bekeley Diffeential Response Diffeential Response (cont d) 05 Sp 008 Lectue, Slide Pof. Wu, U Bekeley 0 R 05 Sp 008 Lectue, Slide Pof. Wu, U Bekeley 0 R 05 Fall 007

3 4//008 Diffeential Pai haacteistics diffeential put sinal esults aiations the output cuents and oltaes, wheeas a coon ode put sinal does not esult any output cuent/oltae aiations. 05 Sp 008 Lectue, Slide 3 Pof. Wu, U Bekeley itual Gound Fo sall put oltaes (+Δ and Δ), the alues ae ~equal, so the cease and decease ae ~equal anitude. Thus, the oltae at node P is constant and can be consideed as ound. +Δ Δ Δ ( Δ ΔP) Δ Δ ΔP Δ Δ Δ 0 ( ) 05 Sp 008 Lectue, Slide 4 Pof. Wu, U Bekeley P Extension of itual Gound t can be shown that if R R, and the oltae at node oes up by the sae aount that the oltae at node B oes down, then the oltae at node does not chane. 0 Sall Sinal Diffeential Ga Sce the output sinal chanes by ΔR when the put sinal chanes by Δ, the sall sinal oltae a is R. Note that the oltae a is the sae as fo a E stae, but that the powe dissipation is doubled. ΔR Δ R 05 Sp 008 Lectue, Slide 5 Pof. Wu, U Bekeley 05 Sp 008 Lectue, Slide 6 Pof. Wu, U Bekeley Lae Sinal nalysis nput/output haacteistics BE BE ln ln S S ln + T e + e + e 05 Sp 008 Lectue, Slide 7 Pof. Wu, U Bekeley out out ( R ) ( R ) ( ) R R tanh T 05 Sp 008 Lectue, Slide 8 Pof. Wu, U Bekeley 05 Fall 007 3

4 4//008 Lea/Nonlea Reions of Opeation Sall Sinal nalysis plifie opeat lea eion plifie opeat non-lea eion 05 Sp 008 Lectue, Slide 9 Pof. Wu, U Bekeley 05 Sp 008 Lectue, Slide 0 Pof. Wu, U Bekeley Half icuits Half icuit Exaple Sce node P is ound, we can teat the diffeential pai as two E half cicuits. out out R out out O 05 Sp 008 Lectue, Slide Pof. Wu, U Bekeley 05 Sp 008 Lectue, Slide Pof. Wu, U Bekeley Half icuit Exaple Half icuit Exaple 3 ( R ) O O3 ( R ) O O3 05 Sp 008 Lectue, Slide 3 Pof. Wu, U Bekeley 05 Sp 008 Lectue, Slide 4 Pof. Wu, U Bekeley 05 Fall 007 4

5 4//008 Half icuit Exaple 4 Diffeential Pai Fequency Response Sce the diffeential pai can be analyzed us its half cicuit, its tansfe function, /O ipedances, locations of poles/zeos ae the sae as that of its half cicuit. R + RE π π 05 Sp 008 Lectue, Slide 5 Pof. Wu, U Bekeley 05 Sp 008 Lectue, Slide 6 Pof. Wu, U Bekeley 05 Fall 007 5