Lab 5: Analog to Digital Conversion 5.1 Introduction 5.2 DAC ...

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LSB12161514131211109Analog Out0-2.55 VDigitalIn3456AD557Vcc (+5V)MSB78CSCE~0.1 UF, ceramicFigure 2: Connection scheme for AD557 DAC. The CS and CE control functions won't beneeded for this lab and should be connected to ground, as shown.5.2.2Look at V out on the oscilloscope. How does the dierence between 00000000 2 and 00000001 2compare to the level of noise? Qualitatively, what kind of frequency spectrum does the noisehave? (That is, which frequencies, if any, seem to be most noticeable?)5.3 A/D in Slow MotionNow we can connect the successive approximation register (SAR) and voltage comparatorto make our rst ADC circuit. The detailed connection scheme is shown in Fig. 3. We willbegin by evaluating this ADC in slow motion, clocking it by hand. The pin connections forthe LM311 comparator are shown in Fig. 4.To enable hand clocking of the SAR, use the prototype board debounced switches connectedas shown in Fig. 5. Finally, provide an adjustable DC analog input by connectingthe analog input (at the 10k resistor) to the variable resistor of the prototype board, asshown in Fig. 6.5.3.1Connect the 8 prototype board LEDs to the SAR outputs Q0 { Q7 so that the present digitalestimate can be directly viewed. Finally, we need to see when the SAR has completed itsconversion cycle: The CC pin goes LOW when the cycle is complete. Connect a separate redLED with a current-limiting resistor ( 470 ), as shown in Fig. 3. The LED should be oduring conversion and turn on when conversion is complete. Finally, notethatpin1oftheSAR is \chip enable" (E); this must be grounded.5.3.2The SAR is a \synchronous" device, so it will start conversion only when the S signal isaccompanied by aclock pulse. Give your device some analog input (measure with a DVMor scope). Now start the conversion and watch the analog estimate (output of DAC) with aDVM and the digital estimate (LEDs) while issuing additional clock pulses by hand. Thebinary search pattern should be evident.2
+5 VIN10k4.7MVcc2 +3113 -Vee7+5 V1k7DClock In974LS503 SARQ0 --- Q73 14Start10CC__E1Vcc (+5)1682470LED161__ 8AD557DAC8/8/LEDs8Figure 3: Connections for slowA/Dcheckout. Consult the data sheet for the pin assignmentsfor the SAR outputs Q 0 {Q 7 .Ground18VccIn 1In 223+_76OutputVee4 5LM311Figure 4: Connections for the LM311 voltage comparator. We should not need to use thebalance adjustment (pins 5 and 6) for this lab. For this lab, use VCC +6 and VEE ,6V.3
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Lab 5: Analog to Digital Conversion 5.1 Introduction 5.2 DAC ...

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