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# LAB3 - UC Berkeley EECS Department EECS 40 Lab B E Boser...

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UC Berkeley, EECS Department B. E. Boser EECS 40 Lab LAB3: Operational Amplifier UID: Enter the names and SIDs for you and your lab partner into the boxes below. Name 1 SID 1 Name 2 SID 2 Sensor Interfaces A very frequent scenario when designing electronic circuits: you need some sensory input, e.g. temperature. You found a sensor (e.g. a thermistor) that converts the actual temperature into an electrical voltage. The next step is to interface the sensor to the rest of your system, typically a computer (microcontroller). Figure 1 shows the setup. Usually the output of the sensor is a small voltage in the milli- or micro-Volt range (for a full-scale signal), while the rest of the electronic system (e.g. the computer) expects much larger signals, typically around a Volt. For example, the scale we built earlier generated output signals that were only a few milli-Volt. To overcome this mismatch we need some kind of interface between the sensor and the computer (or whatever we would like to connect the sensor to), as illustrated in Figure 2 on the next page. Sensor interfaces can perform many functions. Here we focus on the task of gaining up the signal to appropriate amplitude. Specifically, we want the interface to perform the function v 2 = A v v 1 (1) where A v is the voltage gain. For example, if A v = and v 1 = mV, v 2 = 1 pt. 0 We will build the sensor interface out of operational amplifiers. To test it, we need an input, and something to verify the output. We could use the scale constructed in an earlier lab for the input, but this would require us to wire up that circuit again. Moreover, if we encounter problems, we would have to determine if they are due to the interface or the sensor—not always a trivial issue. A better solution is to synthesize an appropriate input v 1 with reliable and well characterized (that’s why it’s expensive) laboratory equipment to test our amplifier circuit. Once we are satisfied with the result we can combine building blocks (and test again). Tackling circuits one-by-one in this fashion significantly simplifies our task and speeds up our work. We will use the signal generator to simulate the sensor and the oscilloscope to verify the output from our sensor interface. Signal Generator and Oscilloscope Download the manuals for the oscilloscope and signal generator and read the quick start and overview guides. Program the signal generator to produce a 1 kHz sinewave with V s = V zero-to-peak amplitude. Connect the signal generator to the oscilloscope as shown in Figure 3 on the following page. Observe the sinewave on the oscilloscope display. What is the zero-to-peak amplitude? Note: the answer is not V s !

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LAB3 - UC Berkeley EECS Department EECS 40 Lab B E Boser...

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