Lab reportIntroduction:

This lab is a review of op-amp with non-inverting configuration, in addition with nonlinear electronics devices such as diode. At the last of this design lab, we have been asked to finish the ADC and display the digital signal with a 7 segments LED display. Overall, this lab processes a certain difficulty to be finished. It is challenging to design the ADC circuit, especially the connection between the ADC converter, the encoder and the display driver. Fortunately, with 2 groups working together, we were able to finish the lab at very last.

Discussions and observations:

Part 1 Multiple Function Generator

This part is testing the basic understanding of simple wave form generator that consisted by op-amps. As we follow the schematic diagram provided in the lab instruction, we built up the circuit and test each terminal with the oscilloscope. We got:

Figure 1 wave form at terminal 1

Figure 2 waveform at terminal 2

Figure 3 waveform at terminal 3

By observing those waveforms and relate them to the integrator. We can see that by each stage, we got an integrated wave. That is, the integration of a square wave is triangular wave; the integration of triangular wave is two parabolas connecting together which seems like a sine wave.

To answer the question at the end of this part, we should relate the circuit to the knowledge we have learned in the lecture. Firstly, the frequency can be altered. This is due to the RC circuit have a certain response to the voltage. We just need to change resistance of any resistor, or change capacitance of any capacitor. We may get a different frequency. Secondly, the amplitude can be changed. The amplitude of the wave is determined by the two bias voltages across the op-amps. So we just need to change the bias voltage to achieve this goal.

Part 2 Absolute Value circuit

This part is a testing of absolute value circuit. Follow the schematic, we built up the circuit. Refer to the absolute value circuit, we may think about the full wave rectifier. This circuit is another wave to implement the full wave rectifier with diodes and op-amp. To test this circuit, we used the function generator we build up in the first part of this lab.

Figure 4 output with Vin as a square wave

Figure 5 output with Vin as a triangular wave

Figure 6 output with vin as a parabolic wave

As we can see that there are some distortion of the waveform, this is due to the non-ideality of the devices.

If we use non-identical diodes in this circuit, we might not get a symmetric wave form through the absolute value circuit. This is because the different forward voltage and current of different diode. The waveforms can even look more distorted through the oscilloscope.

Part 3 Testing an ADC

This is the last part of the lab. As I mentioned above, this part is the most difficult of this lab. Our task is design an A to D circuit and display the output with a seven segments display. The components we used in this circuit are “S4802BJR-H1”, “sn74hc148” “ADC080X” and “CD4055BE”. The ADC receiving an input voltage, then convert it into digital voltage output. The 8 to 3 encoder receive the 8 bits input than encodes it into 3 bits voltage output. The display driver receives 3 bits input than drives the 7 segments display to light up. The 7 segments display, displays the voltage level that is input to the ADC.

With the data sheet of those four devices we hooked up the circuit. This first circuit is to test the digital output of the ADC – analog to digital converter. We took three pictures showing the different voltage level we got the different outputs.

Figure 1 "00000000"

Figure 2 "00010100"

Figure 3 "01111101"

The second part is the number display. We checked every connection through every pin. But we still could not get a perfectly result. For number 2, 4 are in the form of dark bars, which means the bars

should light are not lighted up, the bars should not light up are lighted up. However, we got 1 3 5 works perfectly.

Figure 4 "1" display

Figure 5 "3" display

Figure 6 "5" display

After finish the part, we got a brief idea about how is those complicated devices works and have some insight about the application of those component in the real world.

Conclusion

After doing this final lab for 3 weeks, we have a practical view of what we have learning. In addition, this final lab introduces us the way to design something. We do not need to know exactly how to implement every single electronics devices, but we still can build a functioning circuit if we know what the use of those devices are and got the data sheet of the devices. Hopefully, we made this lab. And we are going to look forward to designing more.