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Unformatted text preview: Indiana U, Physics Dept (H.O. Meyer 7/06) 3- 1 Lab #3: Operational Amplifiers Goal: Learn how to use operational amplifiers (op-amps) with various types of feedback gain control. Equipment : OP-07 op-amp, bread board, assorted resistors and capacitors, DMM, oscilloscope. 1 Introduction: Operational amplifiers (short: op-amps) are voltage amplifiers with very high gain. An op-amp has two inputs: one called non-inverting (label +), and the other inverting (label ). Normally, an op-amp is used with feedback, i.e., the output signal is fed back in some way to affect the input. The function of an op-amp circuit is determined by how this feedback is arranged. The function of a circuit with an op-amp can be understood easily by remembering just two golden rules: No charge flows into or out of either of the two inputs. The output (in whatever feedback scenario) strives to make the voltage difference between the two input zero. Our op-amp is an OP-07, actually an integrated circuit with dozens of transistors, packaged in a mini-DIP ( D ual I n- Line P ackage) with eight pins. You will find a data sheet for the OP07, including the pin assignments, at the end of this document. The circuit is energized by the supply voltages V which we choose as 15 V. If the output wants to exceed the supply voltage, the signal is clipped (see figure). 2 Inverting Amplifier In this application (see figure on the right) the feedback resistor, R 2 , is connected to the inverting input. The input signal is applied through the series input resistor R 1 to the inverting input. The resistor R 3 (equal to the parallel resistance of R 1 and R 2 ) in the non-inverting input minimizes the output-offset voltage caused by the input bias current, but the circuit works quite well with R 3 = 0....
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- Spring '11