Lecture 22B - 67"“) Q 2 <<td 016...

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Unformatted text preview: 67"“) Q 2 <<td 016 ,‘J, +12?ka W \ . gz/ Hyh 0, 19.43 pm We #W'TLO c105: [936 70V: 3 J Huang?) (6J6 km (Iowa) :-.u...-r;4...<-_~.<.1...:.-£. :Im,:_vmflfl=1h_"_u_t magufwm—s. =— A ‘ «Cr-’51.. r320 . V ctr? mu: «055%: 8.6%.: < l .. J - , . , 4': ' 3 1 FM J'églt/n’y, M We- ?'> 6‘3“, 4'0 , .2235) 5‘41. foan'él “‘3‘!!! a") _ ‘zl 63‘” << 6‘91. " B’-‘ I is conrrf-om‘fi/V W'_; M m) swat/alt“?! Ana‘J‘w » i740.“ Ta. Ta . MEETS. 22-141 50 SHEETS 22-142. 1005 22-144 200 SHEETS . B 4' I 7: g 2. f.:;.-'.é.~/.-t’¥zvd: .r' Q Jw/OKAWAVfiw; (a dtgmrg wh/ /b77¢r (o , . _ M PIA—2! ?q°, d~r~ - M4; q +9- 4%;4qu; W, > A 9600’? (6..» Mia/“fin 87-! “7W3 22441 so SHEETS 22142 100 SHEEFS 22.144 zoo SHEETS /MPAJ U ‘ l 18')“; (M toil Waffle a[fl1.+o ((44? C; qui%a7f, C/VQLz/‘é Lfifl 5.2m («um/wa Vauf end :57qu ._1’ g Cw“ (.c (/(J (55¢!) é—fyww; {SE U101 I]: -mm 00 mo ‘— \‘N 9V FF 4 1 NW FIN E m I a) O C) N 3 T N N -A mfg/4H" .., [Kerb/f ‘lxv he I __ 3H?” W' DW‘ 3‘ on N (I, [Ar/d], [4A 79/( A .221__ ELL“? (fmwi'fi'é scuff 4"“ . 46““ IBM“ V2252) _ Q5 Sm 34% . { fl“ Muck/(4451 mp&—~n _ 2.311921”: - EEES320 Bipolar Analog IC Design ' 7' #273 F- 6/ 7 ‘ Op Amp LimitatiOns 0 Gain-Bandwidth. Usually gain is ok at dc; you "use it up" as you go for closed—loop gain. Thus, for example, a 741 is not a good choice for a gain-of-2000 audio amp -- the closed-loop bandwidth is ~ 1 MHz/2000 = 500 Hz! Solutions: use two closed-loop stages; get amp with higher GBW. Use custom-compensated op amp if closed—loop gain is > unity. - Slew rate. Important when fast settling is important (sample/hold circuit for example). Lower Gml/Ibias ratio ratio helps. Use custom compensated op amps if closed-loop gain is > unity. - Input offset voltage. Input voltage required to balance the circuit. A key error source in precision dc circuits. V05 = (Mismatch in input-stage currents)/Gm1. Generally, simpler input stages ' fewer corn onents) ive better V , as do those with higher G /I - ratios. Some am 8 allow p g OS ml bias P this to be adjusted to zero. 0 nput offSet voltage drift. Once the offset is nulled at one time and/or temperature, you can still detect this variation. - Noise. Every resistor automatically generates a' random voltage across its terminals ("thermal noise," due to random motion of electrons). All direct current crossing a junction has a random component ("shot noise," due the quantized charge on the carriers). Therefore, all circuits produce random noise signals. Noise gets Worse at low frequencies (" l/f noise"). Usually lower offset voltage and lower noise at low frequencies go hand-in-hand. - Input bias current. Every op amp input must have a dc path to supply this bias current. It produces a voltage across any resistors present. This is a key limitation for sample/hold circuits, where the bias current discharges the storage capacitor. FET inputs allow much smaller input currents than BITS. - np' ut offset current. Mismatch of the bias currents converts to an offset voltage unless the resistive paths match. Can be nulled along with the rest of the offset voltage. - Input offset current drift. Again, this part remains after the rest is nulled. - Common—mode voltage limitations. Can be limited by input CM range or by output swing. - Output current limits. Most op amps can supply only a few mA. Class—B output stages allow source or sink currents greater than their bias current. 0 Input overload. Simple N PN input stages (low noise, low V03) can be damaged or destroyed when the instantaneous differential input voltage goes above 7 volts (Zener breakdown). This can happen during slewing. Also, capacitors can discharge into the inputs after the power supplies are turned off. Sometimes diode pairs are placed between the inputs to clamp the differential voltage swing to 2 VBE. N1??? 8115: ‘ “9 ”\ 311g ‘4 ._ Ruhr. . In ,\ _ Engineer’s Computaticn Pad M Gina/176‘. /éc‘6~)j M7 féazozvrwm/ g—é-rw , QMMWMQ 7K1. Maggiegi W—mewTXJ’L 43¢)? wMWM 46 fi/rfiflw 7 a/Wfoéwawcf . WO/ how woo/£46 ,"(L ,0 L24 WW1 7 Axum flue? MM £14727,“ Maya/(f4 7:, 171 AM #965st ML % fit fife/7L MW/ M/{ 5%. (-3 #fi C. irzLL‘“ 7: LOLA/{V Is {é S/m 7%; (mm/f (ML-A w c; '7 w~2 CL.th a 6 (90/6; ...
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Lecture 22B - 67&amp;quot;“) Q 2 &amp;lt;&amp;lt;td 016...

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