EXPERIMENT 2 CLIPPING & CLAMPING CIRCUITS

Transcription

1 DOKUZ EYLUL UNIVERTSITY DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING EED 2012 LAB ANALOG ELECTRONICS EXPERIMENT 2 CLIPPING & CLAMPING CIRCUITS Std. No. Name & Surname: Group No : Submitted to: Date : Spring, 2013

2 OBJECTIVE To calculate, draw, and measure the output voltages of series and parallel clipping and clamping circuits. EQUIPMENT REQUIRED (1) 2.2-KΩ (1) 100-kΩ (1) Silicon Diode (1) 1-pF capacitor (1) 1.5-V D cell RESUME OF THEORY The primary function of clippers is to "clip" away a portion of an applied alternating signal. The process is typically performed by a resistor- diode combination. DC batteries are also used to provide additional shifts or "cuts" of the applied voltage. The analysis of clippers with squarewave inputs is the easiest to perform since there are only two levels of input voltage. Each level can be treated as a DC input and the output voltage for the corresponding time determined. For sinusoidal and triangular inputs, various instantaneous values can be treated as DC levels and the output level determined. Once a sufficient number of plot points for the output voltage V o have been determined, it can be sketched in total. Once the behavior of clippers is established, the effect of the placement of elements in various positions can be predicted and the analysis completed with less effort and concern about accuracy. Clampers are designed to "clamp" an alternating input signal to a specific level without altering the peak-to-peak characteristics of the waveform. Clampers are easily distinguished from clippers in that they include a capacitive element. A typical damper will include a capacitor, diode, and resistor with some also having a DC battery. The best approach to the analysis of dampers is to use a step-by-step approach. The first step should be an examination of the network for that part of the input signal that forward biases the diode. Choosing this part of the input signal will save time and probably avoid some unnecessary confusion. With the diode forward biased the voltage across the capacitor and across the output terminals can be determined. For the rest of the analysis it is then assumed that the capacitor will hold on to the charge and voltage level established during this interval of the input signal. The next part of the input signal can then be analyzed to determine the effect of the stored voltage across the capacitor and the open-circuit state of the diode. The analysis of a clamper can be quickly checked by simply noting whether the peak-to-peak voltage of the output signal is the same as the peak-to-peak voltage o f the applied signal. This check is not sufficient to be sure the entire analysis was correct but it is a characteristic of dampers that must be satisfied.

3 PROCEDURE Part 1. Threshold Voltage Determine the threshold voltage for the silicon diode using the diode-checking capability of the DMM or a curve tracer. Round off to hundredths place when recording in the designated space below. If the diode checking capability or curve tracer is unavailable assume V T = 0.7 V for the silicon diode. Part 2. Parallel Clippers a. Construct the clipping network of Fig Record the measured resistance value and voltage of the D cell. Note that the input is an 8 Vpp square wave at a frequency of 1000 Hz. V T = Figure 2.1 b. Using the measured values of R, E, and V T calculate the voltage V o when the applied square wave is +4 V, that is, for the interval when the input is +4 V. What is the level of V o? Show all the steps of your calculations to determine V o. c. Repeat Part 2(b) when the applied square wave is -4 V. d. Using the results of Parts 2(b) and 2(c) sketch the expected waveform for V o using the horizontal axis of Fig.2.2 as the V o = 0 V line. Use a vertical sensitivity of 1 V/cm and a horizontal sensitivity of 0.2 ms/cm.

4 Figure 2.2 e. Using the sensitivities provided in Part 2(d) set the input square wave and record V o on Fig. 2.3 using the oscilloscope. Be sure to preset the V o = 0 V line using the GND position of the coupling switch (and the DC position to view the waveform). Figure 2.3 How does the waveform of Fig.2.3 compare with the predicted result of Fig. 2.2? f. Reverse the battery of Fig. 2.1 and, using the measured values of R, E, and V T, calculate the level of V o for the time interval when V i = +4 V.

5 g. Repeat Part 2(f) for the time interval when V i = -4 V. h. Using the results of Parts 2(f) and 2(g) sketch the expected waveform for V o using the horizontal axis of Fig. 2.4 as the V o = 0 V line. Use the same sensitivities provided in Part 2(d). Figure 2.4 i. Set the input square wave and record V o on Fig. 2.5 using the oscilloscope. Be sure to preset the V o = 0 V line using the GND position of the coupling switch (and the DC position to view the waveform). How does the waveform of Fig. 2.4 compare with the predicted result of Fig. 2.5? Part 3. Series Clippers Figure 2.5 a. Construct the circuit of Fig Record the measured resistance value and the DC level of the D cell. The applied signal is an 8 Vpp square wave at a frequency of 1000 Hz.

6 Figure 2.6 b. Using the measured values of R, E, and V T calculate the voltage V o for the time interval when V i = +4 V. c. Repeat Part 3(b) for the time interval when V i = -4 V. d. Using the results of Parts 3(b) and 3(c) sketch the expected waveform for V o using the horizontal axis of Fig. 2.7 as the V o =0 V line. Insert your chosen vertical and horizontal sensitivities below: Vertical sensitivity = Horizontal sensitivity = Figure 2.7 e. Using the sensitivities chosen in Part 3(d) set the input square wave and record V o on Fig. 2.8 using the oscilloscope. Be sure to preset the V o = 0 V line using the GND position of the coupling switch (and the DC position to view the waveform).

7 Figure 2.8 How does the waveform of Fig 2.8 compare with the predicted result of Part 3(d)? f. Reverse the battery of Fig. 2.6 and using the measured values of R, E, and V T calculate the level of V o for the time interval when V i = +4 V. g. Repeat Part 3(f) for the time interval when V i = -4 V. h. Using the results of Parts 3(f) and 3(g) sketch the expected waveform for V o using the horizontal axis of Fig. 2.9 as the V o = 0 V line. Use the following sensitivities: Vertical: 2 V/cm Horizontal: 0.2 ms/cm Figure 2.9

8 i. Using the sensitivities provided in Part 3(h) set the input square wave and record V o on Fig using the oscilloscope. Be sure to preset the V o = 0 V line using the GND position of the coupling switch (and the DC position to view the waveform). Figure 2.10 How does the waveform of Fig compare with the predicted pattern of Fig 2.9? Part 4. Clamppers (R, C, Diode Combination) a. Construct the network of Fig and record the measured value of R. Figure 2.11 b. Using the value of V T from Part 1 calculate V c and V o for the interval of v i that causes the diode to be in the "on" state. V c (calculated) = V o (calculated) = c. Using the results of Part 4(b) calculate the level of V o after v i switches to the other level and turns the diode "off." V o (calculated) =

9 d. Using the results of Parts 4(b) and 4(c) sketch the expected waveform for V o in Fig for one full cycle of v i. Use the horizontal center axis as the V o = 0 V line. Record the chosen vertical and horizontal sensitivities below: Figure 2.12 e. Using the sensitivities of Part 4(b) use the oscilloscope to view the output waveform V o. Be sure to preset the V o = 0 V line on the screen using the GND position of the coupling switch (and the DC position to view the waveform). Record the resulting waveform on Fig How does the waveform of Fig compare with the expected waveform of Fig. 2.12? Figure 2.13 f Reverse the diode of Fig and using the value of V T from Part 1 determine the levels of V c and V o for the interval of v i that causes the diode to be in the "on" state. V c (calculated) = V o (calculated) =

10 g. Using the results of Part 4(f) calculate the level of V o after V i switches to the other level and turns the diode "off." h. Using the results of Parts 4(f) and 4(g) sketch the expected waveform for V o using the horizontal axis of Fig Use the horizontal center axis as the V o = 0 V line. Record the chosen vertical and horizontal sensitivities below: Figure 2.14 i. Using the sensitivities of Part 4(h) use the oscilloscope to view the output waveform V o. Be sure to preset the V o = 0 V line on the screen using the GND position of the coupling switch (and the DC position to view the waveform). Record the resulting waveform on Fig Figure 2.15 How does the waveform of Fig compare with the expected waveform of Fig. 2.14?

11 CONCLUSION Student Name and ID:

12 CONCLUSION Student Name and ID:

13 CONCLUSION Student Name and ID: