Technte 6 prl 990 Resed /22/02 Op mp Dentns Tm J. Sberng SDE Cnsultng sdecnsultng@pbx.cm 990 Tm J. Sberng. ll rghts resered.
Op mp Dentns Pge 2 Op mp Dentns Ths Technte summrzes the bsc pertnl mpler dentns nd cmpres the del Op mp ssumptns wth the perrmnce rel mplers. Open Lp Gn: () Fgure. Op mp n pen-lp cngurtn Clsed Lp Gn (nertng): r: cl cl ( n) ( n) α (2) (3) Fgure 2. Inertng Op mp cngurtn Inertng mpler blck dgrm: α Σ Fgure 3. Inertng Op mp blck dgrm Clsed Lp Gn (nn-nertng): r: cl cl ( nn) ( nn) (4) (5) Fgure 4. Nn-Inertng Op mp cngurtn Cpyrght 990 Tm J. Sberng. ll rghts resered.
Op mp Dentns Pge 3 Nn-nertng mpler blck dgrm: Σ Lp Gn: Fgure 5. Nn-nertng Op mp blck dgrm l (6) Fgure 6. Dentn lp gn Feedbck Fctr: 2 (7) 2 ( ) α (8) Fgure 7. Dentn eedbck ctr Dertn cl, Inertng mpler Reerrng t Fgure 2 be nd pplyng KCL t the nertng nde: 0 (9) 0 (0) () cl ( n) (2) Cpyrght 990 Tm J. Sberng. ll rghts resered.
Resed /9/02 Pge 4 Cpyrght 990 Tm J. Sberng. ll rghts resered. cl n (3) cl n (4) Recgnzng tht nd α (5) α cl n (6) s cl n α (7) Nte tht Equtn (6) cn ls be expressed s: cl n (8) Dertn cl, Nn-nertng mpler 0 (9) 0 (20) (2) cl nn (22) cl nn (23)
Resed /9/02 Pge 5 Recgnzng tht (24) cl ( nn) (25) s ( nn) cl Equtn (25) cn ls be expressed s: cl ( nn) (27) Equtns (8) nd (27) re ery useul n exmnng the gn errr s unctn requency s the errr term ppers n the sme rm n bth equtns. Ths shws why hgh pen lp gn s mprtnt nd ls why t s ten necessry t select n Op mp wth hgh pen-lp gn nd/r hgher then expected bndwdth. Gn _ Errr (28) Settlng tme s relted, but seprte, prmeter. Due t the delys n prpgtn sgnl thrugh the nternl pmp crcutry, the utput tkes tme t rech t s nl lue. Ths s prtculr cncern r step nputs when slew rte, ersht nd rngng my dmnte the utput respnse. Gn (db) OPEN LOOP GIN (26) CL CLOSED-LOOP BNDWIDTH CLOSED LOOP GIN CL LOG Fgure 8. Open Lp nd Clsed Lp Mgntude Respnses. Cpyrght 990 Tm J. Sberng. ll rghts resered.
Resed /9/02 Pge 6 Idel Op mp ssumptns: R R Fgure 9. Op mp Equlent Crcut Idel Chrcterstc Crcut Eect N current lws n the nputs Ibs(,) 0 r n ltge gn s nnte, 0 N utput ltge r zer nput s 0 Output mpednce s zer ut 0 Frequency respnse s lt nd nnte BW r Dely 0 nd GBW Slew Rte s nnte BW r Dely 0 nd GBW CMRR s nnte Unlmted nput ltge rnge PSRR s nnte Immune t PS set nd rtns Nse ree Output due t sgnl nly Tble. Idel Op mp Chrcterstcs Reltes:. Bs currents cuse sets nd drt. 2. Fnte pen lp gn nd nte bndwdth result n gn errrs exmne lp gn term,, n Equtns (6) nd (25). 3. Input resstnce (mpednce) ntrduces errrs ppers n prllel wth. 4. Output resstnce (mpednce) ntrduces errrs ppers s ltge dder wth nd the ld. 5. Oset ltge ppers t the utput multpled by the nse gn. Oset ltge ls drts er tme due t temperture chnges. 6. Bs currents cuse sets nd re nt mtched between the nputs. They ls drt er tme due t temperture chnges. 7. Pwer supply msmtch cuses sets ppers s cmmn mde ltge t the nput. 8. CMRR s nt nnte s the nput ltge rnge s lmted nd nnlnertes pper n the putput s result cmmn mde ltges, prtuculrly n the nn-nertng cngurtn. 9. Rel Op mps he nse. 0. Op mps he grup dely,.e. nt ll requences experence the sme tme dely thrugh the crcut. Ths results n dstrtn.. Fnte slew rte cn result n utput dstrtn. Cpyrght 990 Tm J. Sberng. ll rghts resered.