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# The university of iowa fall 2011 question 8 an op amp

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Unformatted text preview: 11. Question 8 An op-amp is ideal except that it has a finite open-loop gain . The op-amp is connected in an inverting configuration using two resistor and . (a) Show that the closed-loop gain is ( ) (b) Determine ⁄ such that the closed-loop gain is the open-loop gain is ? (1 5 points) . (b) What is the closed-loop gain if Solution Part (a) Consider the inverting amplifier shown. KCL at the inverting input gives ( ⁄ Note that with finite gain, so that or , but since , . Thus, the KCL equation becomes ⁄ ⁄ ( ⁄ Solving for the closed-loop gain )( yields the desired expre ssion: ( Part (b) Set Part (c) Using and ⁄ ) and solve to find and yeilds 9 ) ⁄ 55:041 Electronic Circuits. The University of Iowa. Fall 2011. Question 9 In the noninverting op-amp amplifier shown, the op-amp is ideal except for a finite open-loop gain and differential-mode input resistance (a) Draw an equivalent model that uses a voltage -controlled voltage ⁄ . (b) source and use the model to derive an expression for Use the model to derive an expression for the input resistance (c) Calculate and for and (1 5 points) This problem is poorly-posed and will not be graded 10 55:041 Electronic Circuits. The University of Iowa. Fall 2011. Question 1 0 The circuit shown is a representation of the common-mode and differential-input signals to a difference amplifier. One can write the output voltage as , where is the differential-mode gain and is the common-mode gain. Assuming an ideal op-amp, one can show that the common-mode gain is ( ) ( ⁄ Further, if , and one can show that the differential-mode gain is | | circuit above, , and . If the tolerance of each resistor is determine the minimum CMRR (in dB). ⁄ . For this , Hint: consider using tools such as Excel or Matlab to search for the resistor combination that result in minimum CMMR. (1 0 points) Solution | This will have minimum value when | spreadsheet the largest is when | is the largest | ( ( ( ( | | is the smallest. Using an Excell ( ( ( ( Then ( ( Further...
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## This note was uploaded on 10/26/2013 for the course ECE 55:041 taught by Professor Kruger during the Fall '11 term at University of Iowa.

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