exp04 - Electronic Instrumentation Experiment 4 * Part A:...

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Unformatted text preview: Electronic Instrumentation Experiment 4 * Part A: Introduction to Operational Amplifiers * Part B: Voltage Followers * Part C: Integrators and Differentiators * Part D: Amplifying the Strain Gauge Signal Part A Introduction to Operational Amplifiers Operational Amplifiers Op-Amp Circuits The Inverting Amplifier The Non-Inverting Amplifier Operational Amplifiers Op-Amps are possibly the most versatile linear integrated circuits used in analog electronics. The Op-Amp is not strictly an element; it contains elements, such as resistors and transistors. However, it is a basic building block , just like R, L, and C. We treat this complex circuit as a black box. The Op-Amp Chip The op-amp is a chip, a small black box with 8 connectors or pins (only 5 are usually used). The pins in any chip are numbered from 1 (starting at the upper left of the indent or dot) around in a U to the highest pin (in this case 8). 741 Op Amp or LM351 Op Amp Op-Amp Input and Output The op-amp has two inputs, an inverting input (-) and a non-inverting input (+), and one output. The output goes positive when the non-inverting input (+) goes more positive than the inverting (-) input, and vice versa. The symbols + and do not mean that that you have to keep one positive with respect to the other; they tell you the relative phase of the output. (V in =V 1-V 2 ) A fraction of a millivolt between the input terminals will swing the output over its full range. Powering the Op-Amp Since op-amps are used as amplifiers, they need an external source of (constant DC) power. Typically, this source will supply +15V at +V and -15V at -V. We will use 9V. The op-amp will output a voltage range of of somewhat less because of internal losses . The power supplied determines the output range of the op-amp. It can never output more than you put in. Here the maximum range is about 28 volts. We will use 9V for the supply, so the maximum output range is about 16V. Op-Amp Intrinsic Gain Amplifiers increase the magnitude of a signal by multiplier called a gain -- A. The internal gain of an op-amp is very high. The exact gain is often unpredictable. We call this gain the open-loop gain or intrinsic gain . The output of the op-amp is this gain multiplied by the input 5 6 out open loop in V A 10 10 V =- ( 29 2 1 V V A V A V ol in ol out- = = Op-Amp Saturation The huge gain causes the output to change dramatically when (V 1-V 2 ) changes sign. However, the op-amp output is limited by the voltage that you provide to it. When the op-amp is at the maximum or minimum extreme, it is said to be saturated . saturation negative V V then V V if saturation positive V V then V V if V V V out out out- < + + - 2 1 2 1 How can we keep it from saturating? Feedback Negative Feedback As information is fed back, the output becomes more stable. Output tends to stay in the linear range. The linear range is when V...
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exp04 - Electronic Instrumentation Experiment 4 * Part A:...

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