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# mid00c - Your Name Student Number 3 Question 3(4 marks An...

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Unformatted text preview: Your Name: Student Number: 3 Question 3. (4 marks) An opamp when loaded with 2 pF has a slew rate of 40 Vhisecond. This opamp is connected to capacitors as shown in the ﬁgure below. An input step of 1.5 V is applied as shown on the plot. lpF 2.0 ._,,,,..,..,.:.:...,' : : : :Vi: : : : : : : : : : 1 F 1.5 ........ . . . . . v P 1.0 ‘ ..................................................... l ——| v 0.5 ..... ........ : o 0.0 i .. E ......... 7 ........ :.. .. ., ......... ,.:. g : 100 I 1505 2005 25 3 300 fume lpF -0.5 .. ‘,,‘, .......... nsec 4 a) Plot the resultant output voltage on the plot above showing approximate slope, over- shoot, ﬁnal settled voltage, etc. Assume the initial output voltage at t = 0 is 0V. {nitml S [K6 é‘x V; : 051/ For 559(0ij Maw/in é QP2§£”’/€' with (11°F §€n‘8)5 mt J/F) =2 Afa/ Lift s/ew mic ,: F X ‘WV/asec — 553W sec F,‘nq/ value 4.6 [gm/n: -I) Question 4. (5 marks) An opamp has a DC gain of 2000. a) It is desired to use this opamp to design a bandpass ﬁlter with a gain of 6 dB at the centre frequency of 1 MHz. In order to keep the gain error to about 1%, estimate the frequency for the dominant pole of this opamp. 2000 Desl‘reﬂl 94in : J6 :' 7” or 646))” 3:05. 200 .2 Gain ermr : 0-0/= 7r?) A9=Ioo 4,4: 200» ,1 «— DC gain : 2000] Meow/e down ,9am:201> 2 ~ _ l : MM; ,0 : [Do/7,42 v, b)'Est1mate the frequency of the second, parasitic pole to provide about 45° of phase margin, with dominant pole as found in a). ‘ Need to separate Poles by DC gain ,5 \$97,: 1}. XDCga/n =2 100K xzooo .-. 200MH1 c) In an opamp, if you double all the transistor widths, leaving lengths the same, estimate the new DC gain. 112' gm do“ 85) 9e; 0‘1 I85 jjam rernams Same. (We, assumed bias uoHa/oe) hence Var! remain; 15kg Sande.) ...
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