13.6: Procedure

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13.6.1: Precision Half-wave Rectifier and Detector

1. The circuit of Figure 13.5.1 is a precision half-wave rectifier. Without C, the circuit responds as an “ideal diode” allowing only positive half-waves through. The addition of C turns the circuit into peak detector or analog pulse-stretcher. Since all of the circuits in this exercise can produce DC components in the output signals, it is very important to take measurements with the oscilloscope input set to DC coupled.

2. Assemble the circuit of Figure 13.5.1 without the load capacitor.

3. Set the generator to a 1 kHz sine wave, and set its output voltage to 1 volt peak.

4. Measure \(V_{out}\) and save a copy of the oscilloscope display as Graph 1. Also measure and save the waveform at the output pin of the op amp as Graph 2.

5. Reverse the diode, measure \(V_{out}\) and save a copy of the oscilloscope display as Graph 3.

6. While monitoring the load voltage, increase the frequency of the generator and note how the distortion in the waveform increases. If a considerably faster or slower op amp is available (in terms of \(f_{unity}\) and slew rate), repeat this process and compare the frequencies at which the two op amps start to distort.

7. Return the diode to its original orientation and add C = 10n F.

8. Apply a 1 volt peak 1 kHz pulse waveform with 10% duty cycle to the input of the circuit.

9. Measure \(V_{out}\) and save a copy of the oscilloscope display as Graph 4.

10. Replace the 10n F load capacitor with a 1\(\mu\) F capacitor. Measure and save the \(V_{out}\) waveform as Graph 5.

13.6.2: Precision Full-wave Rectifier

11. Decide on a value for \(R\) in Figure 13.5.2 and assemble it. The actual value of \(R\) is not critical. The important thing is that the resistors should be close in value, preferably within a few percent of each other.

12. Set the generator to a 1 kHz sine wave, and set its output voltage to 1 volt peak.

13. Record the waveforms at the cathode of \(D_2\) and at \(V_{out}\) as Graph 6.

14. Reverse the polarity of the diodes and record the waveforms at \(D_2\) and at \(V_{out}\) as Graph 7.

15. Try several different input wave shapes (square, triangle, ramp, etc.) while monitoring \(V_{out}\) and note the resulting shapes.

16. Set the generator to a 1 volt peak 100 Hz sine wave and place the oscilloscope in XY mode.

17. For Graph 8, plot the transfer characteristic of the circuit by placing the X (horizontal) probe at the generator, and the Y (vertical) probe at the load \((V_{out})\).

13.6.3: Troubleshooting

18. Continuing with the circuit of Figure 13.5.2, estimate and then measure the results for each individual error presented in Table 13.7.1.

13.6.4: Computer Simulation

19. Build the circuit of Figure 13.5.1 in a simulator using a 351 op amp and without the load capacitor. Run a Transient Analysis to determine the voltages at the output pin of the op amp and at \(V_{out}\). Compare the waveforms to those recorded as Graphs 1 and 2.