LABORATORY PRACTICAL 10

LABORATORY PRACTICAL 10

SAMPLE AND HOLD CIRCUIT

Introduction

This report summarizes an experiment to familiarize with the fundamentals of a Sample and Hold (S/H) circuit and creating it in Multisim. An S/H circuit is an essential tool with many uses, including Digital Interface Circuits and Analog-to-digital Converters.

The objective of the experiment

To familiarize students with the basics of an S/H circuit and creating it in Multisim.

Equipment and Materials

• Connecting Wires
• Power Source
• Oscilloscope
• Breadboard
• Multisim
• Digital Multimeter
• Jumpers
• Capacitor
• LM-741 Op-amp
• 4066 Quad Bilateral Switch

PROCEDURE

Section I

1. Using a Capacitor adjusted to 10nF, two LM-741 Op-amp, and a 4066 Quad Bilateral Switch, create a sample and hold circuit with Multisim software.
2. Use the Multisim digital clock to set the 4066 Quad Bilateral Switch at 200Hz.
3. With one channel of the Oscilloscope connected to the input signal, connect the second channel to the S/H circuit’s output.
4. Simulate the created S/H circuit.
5. Expand the Oscilloscope and use the blue and red cursors to determine the voltage droop of the S/H circuit. Record the results.
6. Print the display results of the enlarged Oscilloscope and the schematic showing the droop measurements.

Section II

1. Manipulate the circuit developed in above Section I of this experiment such that the droop measurement recorded is either 10mV or less.
2. Print the display results of the enlarged Oscilloscope and the schematic showing the droop measurements.

Section III

1. Build the S/H circuit as instructed in Section I of this experiment, and record the same voltage droop measurements.
2. Adjust the frequency of the generator clock to 800Hz. Measure and record the droop of the circuit.
3. Print the display results of the enlarged Oscilloscope and the schematic showing the droop measurements.

RESULTS AND DISCUSSION

A Sample and Hold (S/H) circuit is an essential tool with many uses, including Digital Interface Circuits and Analog-to-digital Converters. This electronic circuit samples the voltage supplied as the input and retained this sample for a definite time. Sampling time refers to the period when the S/H circuit generates a typical amount of the voltage. At the same time, the duration during which the Capacitor holds the sampled value is the holding time. In this experiment, the LM-741 Op-amp acts as a voltage follower, while the Capacitor acts as a charge storage device.

Upon turning on the switch, the Capacitor charges to its threshold and holds the sampled voltage when turned off, until the next charge. The figure below shows a simple S/H circuit, where V_in refers to the input signal, C_h the Capacitor, C_i is the signal from the clock, while V_out is the resultant S/H output signal.

 

Figure 1.0 Showing a simplified S/H circuit

Section I

• When the procedure outlined in above Section I (steps 1-4) were followed, the following simulation resulted:

 

Figure 2.0 Showing Multisim Simulation after following Steps 1-4 of Section I

• Following the steps 5-6 of Section I to the letter, the following waveform resulted in the monitor of the enlarged Oscilloscope.

 

Figure 3.0 Showing the resultant waveform upon enlarging the Oscilloscope.

Section II

• However, the manipulation of the circuit developed in above Section I to produce a droop measurement of 10mV or less resulted in the following simulation in Multisim:

 

Figure 4.0 Showing Multisim Simulation after following Steps 1-2 of Section II

Section III

• The following simulation resulted in Multisim upon implementing the procedure outlined in Section III (steps 1-3):