HomeworkAssignment02Solution

Part c the current in the resistor in the t network

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Unformatted text preview: e current in the resistor in the T-network is magnitude of the current is ⁄ ( ⁄( . The Part (d) The negative sign of associated with the current determined in Part (c) indicate that the current flows though R from the ground into the junction of the T-network. i 3 55:041 Electronic Circuits. The University of Iowa. Fall 2011. Question 3 For the amplifier shown, determine (a) the ideal closed-loop voltage gain. (b) What is the actual closed-loop voltage gain if the open-loop gain is and the op-amp is otherwise ideal? (c) What is the minimum open-loop gain such that the closed-loop gain is within 1% of the ideal? (12 points) Solution Part (a) For an ideal op-amp, and so that the circuit is a follower and . Part (b) With finite open-loop gain, there is a voltage difference ⁄ between the and Assuming , an equivalent circuit that captures the voltages is shown in (a) below. (a) (b) Applying KVL around the loop shown in (b) gives Part (c) From part (b) we have This must be within 1% of the ideal case ( Solving yields ), or . 4 inputs. 55:041 Electronic Circuits. The University of Iowa. Fall 2011. Question 4 Consider the follower shown below. Except for a finite open-loop gain ideal. Derive an expression for the closed-loop gain. (8 points) , the op-amp is Solution With finite open-loop gain, there is a voltage difference ⁄ between the and inputs. Assuming , an equivalent circuit that captures the voltages is shown in (a) below. (a) (b) Applying KVL around the loop shown in (b) gives 5 55:041 Electronic Circuits. The University of Iowa. Fall 2011. Question 5 Consider the current-to-voltage converter circuit shown. The current source has a finite output resistance , and the op-amp is ideal except for a finite open-loop gain . (a) Show that the ⁄( input resistance indicated in the figure is given by . (8 points) Solution P art (a) Determining the input resistance is equivalent to determining the Thevenin equivalent resistance, which we do as follows: turn off independent sources add a test voltage and determine the resulting ⁄ . To turn off a current source,...
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