CP/PC364 Data Communications & Networks Laboratory

D/A Conversion

Overview

Digital transmission of analog data, (such as sound and video), requires analog input signals to be converted to digital signals for processing. Once received, the signals then have to be converted to back analog. These conversions are done by analog to digital (A/D) and digital to analog (D/A) converters, respectively. Although you could construct these converters from discrete components, integrated circuits specifically designed for these purposes are usually used.

Objectives

The objectives for this lab are:

to test the D/A IC for proper operation
to investigate the effects of the D/A conversion process

Do not dismantle the D/A circuit. Store this circuit in your lockup area for use later.

Preparation

Great care should be taken to avoid static discharge into CMOS based chips.

Before starting the lab, review the CMOS handling procedures.

Always use a ground strap. If your grounding mat doesn't have two grounding straps, one for each of the partners, see the lab instructor.
CMOS devices should be stored pin down in conductive foam when they are not in a circuit.
Never leave unused inputs floating; connect to ground or +5V to prevent excessive current consumption and erratic behaviour.
Never connect an input signal to a CMOS device when the power is off.

Equipment

bench supply, oscilloscope, function generator
breadboard, debugger board, resistors, capacitors
DAC0800 [PDF: 11 pages], a digital-to-analog converter from National Semiconductor
LM 336-5.0 5.0 V zener diode [PDF: 11 pages]

Task

To wire the DAC, there are 3 different sub-circuits to wire. They are:

Voltage reference
Supply voltages and inputs
Outputs

You will wire each of these sections in turn.

Wire up the zener diode with an appropriate resistor to produce a 5 V reference voltage.
Demonstrate your circuit to the lab supervisor.
Look in the data sheet for the DAC0800 at FIGURE 3. Basic Positive Reference Operation. Which of the capacitors shown are filter capacitors? Will the circuit work if they are omitted? Why are they there?
Note: All of the connections shown should be part of any circuit. Figures 4 to 13, for instance, don't show any power (or input!) connections so they assume wiring as in Figure 3.
Wire up the DAC input and power supply connections as shown in Figure 3.
Look in the data sheet for the DAC0800 and find the diagram showing the output configuration which will give a single, positive output referenced to ground. This is the configuration you want to use. It will be one of the sample circuits from Figure 6 to Figure 10. (Hint: Which of the figures shows a circuit with a single output? Which of the figures shows a circuit with a positive output?)
Wire up the output circuitry according to the figure you have chosen.
Connect the voltage reference you wired above, if you have not already done so, according to Figure 3. If you have done everything correctly, you should have a circuit which can take in an 8-bit digital value and produce an appropriate analog output between 0 and 5 volts.
Demonstrate your circuit to the lab supervisor. Keep this circuit for future labs.