MOSFET Amplifier Design Project Electrical Engineering 0 Section 00 Shawn Moser
Introduction: In this lab, my partner and I were tasked with the construction of a linear electronic circuit that functions as a simple temperature sensor. In the first part of the design, we will connect an AD 90 transducer device, modeled as a simple Thevenin circuit, to a set of op amps that will output two voltage ranges that represents temperate as a ranges of voltage levels representing both Kelvin and Fahrenheit temperature. Once these circuits are complete, the output of the Fahrenheit output circuit will be connected to a temperate controller circuit. This circuit is constructed to a simple comparator circuit with two LEDs to represent a detection circuit when the temperature, and voltage level, falls out of a certain range. Finally, we will test these circuit against both expected operation and simulations that we ran on Multisim. Circuit Design: To begin this design experiment, we first must construct a circuit to convert the current output from the transducer device, to a voltage range that we can easily work with to adjust via op-amp gain. To do so, we use a simple current-voltage converter circuit, depicted below. This circuit will take the input current, represented by the current source I, and run it through an op amp circuit that will output a voltage signal that matches the current signal input. R kω U I.8uA khz 0 R 00kΩ V Figure : Current-voltage Converter While this current-voltage converter is the circuit that we used when constructing the simulation of the circuit function, we end up replacing this circuit with a simple inverting amplifier circuit. This is required as we must us a voltage source and resistance to represent the alternating current source. Doing so changes the requirement of the circuit we no longer need to convert between current and voltage and allows us to use a simple inverting amplifier to output the same voltage levels to the signal conditioning section of the circuit.
R.kΩ V 0. Vpk khz 0 R 98.kΩ U V Figure : Current-voltage Converter Equivalent Circuit The output of this equivalent voltage converter circuit is then connected to the non-inverting rail of the circuit in figure to achieve the voltage range of.8 V to.v, which is meant to represent the Kelvin temperate range of 8. K to 0.9 K, the range of temperature which the circuit is expected to operate on. This voltage range is achieved via this circuit by achieving a gain of roughly -9 V/V to invert the signal outputted by the current-voltage converter. By inverting this signal, we essentially just undo the initial inversion that takes place in the converter and amplifies the circuit output to the voltage to degree conversion factor that we wish to meet. R 89.kΩ R U 9.89kΩ V Figure : V 0 Signal Conditioning Circuitry The second signal conditioning circuit is much more involved than that for the Kelvin signal conditioning output. The circuit works by using a summing amplifier configuration in order to perform a linear transformation on the input signal from the current-voltage converter circuit. This summing amplifier transforms the input voltage range to roughly 0. V to - V and then outputs it to a simple inverting amplifier to achieve the desired voltage range of V to 0 V. Make not that in order to achieve the correct transformation, we use a biasing voltage of that is achieved by running the V EE rail through a voltage divider and into a voltage buffer. This allows
us to input a necessary voltage level to the summing amplifier while separating the effects of the voltage dividers resistance from the summing amplifier. R 0.kΩ U R.kΩ R V.kΩ R8.kΩ U R0 98.8kΩ R 999kΩ U V R9 V.88Ω Figure : V 0 Signal Conditioning Circuitry This final circuit, is a simple comparator circuit that is meant to turn on an LED when the voltage input falls out of the range of.8 V and. V. The LED represents a cooling or heating component that would return the temperate to the acceptable range. This circuit requires that we simple setup voltage levels of.8 V and. V that we achieve by attached the V EE supply to a voltage divider network. We then connect these voltages to the op-amp inputs in order to compare them to the input levels. In this configuration, if the voltage from the input is above. V or below.8 V, then the respective op-amp output will saturate and a current will pull through the diode, lighting it. Along with the LED, a resistor is connected in series to induce a limited current flow through the LED, and not cause it damage.
V R.kΩ V U LED R kω R.kΩ U LED R kω R.kΩ V Figure : Temperature Controller Data and Graphs: In our initial circuit simulations, we expected to have ideal, discrete resistance values to use to achieve a precise gain. Unfortunately, due to tolerances and error in production, the resistance values that we discovered and used in the actual circuit were not the precise values we hoped to. The following list of resistor values is those that we used, along with the value we ideally would use. Signal Conditioning Circuit Ideal Resistance Actual Resistance R 0 kω 98.kΩ R 00 kω. kω R kω. kω R 0 kω 9.89 kω R 90 kω 89. kω R 0 kω 0. kω R. kω. kω R8 8.0 kω. kω R9 8.0 kω.88k kω R0 00 kω 98.8 kω R MΩ 999 kω
Comparator Circuitry R 8 kω. kω R kω. kω R 8 kω. kω Figure : Current-voltage Converter Output Figure : V 0 Circuit Output
Figure 8: V 0 Circuit Output Figure 9: Temperature Controller 8 Degree Test
Figure 0: Temperature Controller 8 Degree Test Discussion: Summary & Conclusion: Overall, our circuits worked closely to the values that we expected. While there were errors in both of our signal conditioning circuits, much of this was a result of inaccurate resistance values in each of our op-amp designs, along with small error that we found in the oscilloscope display being used. Our circuits worked to the specifications that we expected, especially the comparator circuit, and provided us insight on how to use operational amplifier circuits, and their respective gains, to achieve linear transformations of signal inputs. 8