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Example 7 1.6 kΩ 400 Ω _ 2 kΩ 1.5 kΩ + 3 kΩ _ + + vo 2V + _ _ Calculate v o . The circuit has two operational amplifiers. For the first op amp, the inverting terminal is connected to ground through a 400Ω resistor and a feedback resistor is connected between the inverting terminal and the output node. The output voltage of the first op amp becomes one of the input voltages of the second op amp. We want to find the output voltage of the second op amp. Firstly we need to determine the output voltage of the first op amp, which can be labeled as v1 . There is zero voltage across the two input terminals of the ideal op amp. So the inverting terminal voltage should be equal to that of the non inverting terminal. That is 2V. The input currents should be zero for both of the input terminals. The current flow through the 400Ω resistor is the same as that through the 1.6kΩ resistor. The current passes the 400Ω resistor is the voltage drop across that divided by the resistance. That is two volts minus 0, and then divided by 400Ω. The current flows through the 1.6kΩ resistor is the output voltage of the op amp subtracted by 2, and divided by 1.6kΩ. We got v 2 2 1 400 1600 Both sides of the equation are multiplied by 1600, we get, 8 v1 2 So v1 10V . The 10V is connected to the second op amp through a 2kΩ resistor. Voltages at the two input nodes are equivalent. So the voltage for the inverting node should be 0V since inverting node is grounded. Apply KCL at the inverting node of the input, we got v 10 2 o 0 2k 1.5k 3k Solve for v o 3k 10 2k 2 19V 1.5k