Chapter 15 Interfacing to the Analog World 1. Objectives You should be able to: Perform the basic calculations involved in the analysis of operational.

Chapter 15Chapter 15

Interfacing to the Analog Interfacing to the Analog WorldWorld

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ObjectivesObjectives

You should be able to:You should be able to: Perform the basic calculations involved in Perform the basic calculations involved in

the analysis of operational amplifier the analysis of operational amplifier circuits.circuits.

Explain the operation of binary-weighted Explain the operation of binary-weighted and R/2R digital-to-analog converters.and R/2R digital-to-analog converters.

Make the external connections to a digital-Make the external connections to a digital-to-analog IC to convert a numeric binary to-analog IC to convert a numeric binary string into a proportional analog voltage.string into a proportional analog voltage.

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ObjectivesObjectives

(Continued)(Continued) Discuss the meaning of the Discuss the meaning of the

specifications for converter ICs as given specifications for converter ICs as given in a manufacturer’s data manual.in a manufacturer’s data manual.

Explain the operation of parallel-Explain the operation of parallel-encoded counter-ramp, and successive-encoded counter-ramp, and successive-approximation analog-digital approximation analog-digital converters.converters.

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ObjectivesObjectives

(Continued)(Continued) Make the external connections to an Make the external connections to an

analog-to-digital converters IC to analog-to-digital converters IC to convert an analog voltage to a convert an analog voltage to a corresponding binary string.corresponding binary string.

Discuss the operation of a typical data Discuss the operation of a typical data acquisition system.acquisition system.

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Digital and Analog Digital and Analog RepresentationsRepresentations

An analog An analog signal can be signal can be represented represented with digital with digital values at some values at some time interval.time interval.

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Digital and Analog Digital and Analog RepresentationsRepresentations

Four binary positions = 4-bit Four binary positions = 4-bit resolutionresolution 16 different representations16 different representations

Eight binary positions = 8-bit Eight binary positions = 8-bit resolutionresolution 256 different representations256 different representations

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Operational Amplifier Operational Amplifier BasicsBasics

Very high input impedanceVery high input impedance Very high voltage gainVery high voltage gain Very low output impedanceVery low output impedance

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Discussion PointDiscussion Point Determine VDetermine Voutout

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Binary-Weighted Digital-Binary-Weighted Digital-to-Analog Convertersto-Analog Converters

Sum of the currents from the input Sum of the currents from the input resistorsresistors

Binary weighting factorBinary weighting factor

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Binary-Weighted Digital-Binary-Weighted Digital-to-Analog Convertersto-Analog Converters

Accurate resistance over a wide Accurate resistance over a wide range is difficultrange is difficult

Not practical for conversions greater Not practical for conversions greater than 4-bitthan 4-bit

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R/2R Ladder Digital-to-R/2R Ladder Digital-to-Analog ConvertersAnalog Converters

Only two resistor valuesOnly two resistor values 8, 10, 12, 14, and 16 bit 8, 10, 12, 14, and 16 bit

resolutions are commonresolutions are common

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R/2R Ladder Digital-to-R/2R Ladder Digital-to-Analog ConvertersAnalog Converters

Current division and analog output Current division and analog output versus digital inputversus digital input

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R/2R Ladder Digital-to-R/2R Ladder Digital-to-Analog ConvertersAnalog Converters

Current division and analog output Current division and analog output versus digital inputversus digital input

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Integrated-Circuit Digital-Integrated-Circuit Digital-to-Analog Convertersto-Analog Converters

DAC0808 block diagram and pin DAC0808 block diagram and pin configurationconfiguration

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Integrated-Circuit Digital-Integrated-Circuit Digital-to-Analog Convertersto-Analog Converters

DAC0808 ApplicationDAC0808 Application

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Integrated-Circuit Digital-Integrated-Circuit Digital-to-Analog Convertersto-Analog Converters

Testing the 256-step output of a Testing the 256-step output of a DAC with an 8 bit counterDAC with an 8 bit counter

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Integrated-Circuit Digital-Integrated-Circuit Digital-to-Analog Convertersto-Analog Converters

Multisim DAC simulationMultisim DAC simulation

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IC Data Converter IC Data Converter SpecificationsSpecifications

Differential nonlinearityDifferential nonlinearity Gain errorGain error Missing codesMissing codes

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IC Data Converter IC Data Converter SpecificationsSpecifications

Nonmonotonic, offset error, relative Nonmonotonic, offset error, relative accuracy, settling time, and 3-bit ADC accuracy, settling time, and 3-bit ADC transfer characteristictransfer characteristic

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Parallel-Encoded Analog-Parallel-Encoded Analog-to-Digital Convertersto-Digital Converters

Parallel encodingParallel encoding Also called simultaneous, multiple Also called simultaneous, multiple

comparator, or flash convertingcomparator, or flash converting Several comparators with different Several comparators with different

reference voltages drive a priority reference voltages drive a priority encoderencoder

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Parallel-Encoded Analog-Parallel-Encoded Analog-to-Digital Convertersto-Digital Converters

Three-bit Three-bit parallel parallel encoded ADCencoded ADC

priority priority encoderencoder

Analog range Analog range of 0-7 Vof 0-7 V

3 bit (8 level) 3 bit (8 level) resolutionresolution

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Counter-Ramp Analog-Counter-Ramp Analog-to-Digital Convertersto-Digital Converters

Counter used in conjunction with a Counter used in conjunction with a D/A converterD/A converter

To change for continuous To change for continuous conversions end-of-conversion line is conversions end-of-conversion line is tied back to clear inputtied back to clear input

Disadvantage is slow conversion Disadvantage is slow conversion timetime

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Counter-Ramp Analog-Counter-Ramp Analog-to-Digital Converters to-Digital Converters

(Figure 15-12)(Figure 15-12)

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Successive-Successive-Approximation Analog-Approximation Analog-to-Digital Conversionto-Digital Conversion

Most used in modern ADC ICsMost used in modern ADC ICs Converter circuit is similar to counter-Converter circuit is similar to counter-

rampramp Uses successive approximation register Uses successive approximation register

to quickly narrow in on the analog valueto quickly narrow in on the analog value Result is a much faster conversion when Result is a much faster conversion when

compared to the counter-ramp methodcompared to the counter-ramp method

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Successive-Successive-Approximation Analog-Approximation Analog-to-Digital Conversionto-Digital Conversion

Simplified SAR A/D converterSimplified SAR A/D converter

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Integrated-Circuit Analog-Integrated-Circuit Analog-to-Digital Convertersto-Digital Converters

NE5034 – similar to the SAR ADC NE5034 – similar to the SAR ADC just presented but uses a three-state just presented but uses a three-state output buffer instead of a D flip-flopoutput buffer instead of a D flip-flop

Conversion speeds up to 17 Conversion speeds up to 17 ss Compatible with bus oriented Compatible with bus oriented

microprocessorsmicroprocessors

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Integrated-Circuit Analog-Integrated-Circuit Analog-to-Digital Convertersto-Digital Converters

NE5034 block diagram and pin NE5034 block diagram and pin configurationconfiguration

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Integrated-Circuit Integrated-Circuit Analog-to-Digital Analog-to-Digital

ConvertersConverters ADC 0804ADC 0804

Successive-approximationSuccessive-approximation Two analog inputs for differential Two analog inputs for differential

measurementsmeasurements Internal clock (determined by external Internal clock (determined by external

R and C)R and C) Operation similar to NE5034Operation similar to NE5034 Analog and digital ground are both Analog and digital ground are both

providedprovided

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Integrated-Circuit Integrated-Circuit Analog-to-Digital Analog-to-Digital

ConvertersConverters ADC 0804 block diagram and pin ADC 0804 block diagram and pin

configurationconfiguration

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Data Acquisition System Data Acquisition System ApplicationApplication

Data busData bus Control busControl bus Analog Multiplexer Switch (AM3705)Analog Multiplexer Switch (AM3705) Sample-and-Hold Circuit (LF198)Sample-and-Hold Circuit (LF198) Programmable-Gain Instrumentation Programmable-Gain Instrumentation

Amplifier (LH0084)Amplifier (LH0084) Analog-to-Digital Converter Analog-to-Digital Converter

(ADC0804)(ADC0804)

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Data Acquisition System Data Acquisition System ApplicationApplication

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Transducers and Signal Transducers and Signal ConditioningConditioning

Physical quantities to electrical Physical quantities to electrical quantitiesquantities

Must be conditioned due to different Must be conditioned due to different output ranges and signalsoutput ranges and signals

Manufacturers specifications must be Manufacturers specifications must be studiedstudied

Analog output of transducer is Analog output of transducer is converted to binary by ADCconverted to binary by ADC

Data can then be manipulated by Data can then be manipulated by softwaresoftware

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Transducers and Signal Transducers and Signal ConditioningConditioning

Thermistor resistance is dependent on Thermistor resistance is dependent on temperature and response is nonlineartemperature and response is nonlinear

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Transducers and Signal Transducers and Signal ConditioningConditioning

Thermistors – Example conversion Thermistors – Example conversion circuitcircuit

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Transducers and Signal Transducers and Signal ConditioningConditioning

Linear IC Linear IC Temperature Temperature SensorsSensors Simplify Simplify

process of process of converting a converting a nonlinear nonlinear responseresponse

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Transducers and Signal Transducers and Signal ConditioningConditioning

The Strain GageThe Strain Gage Resistance changes when stretchedResistance changes when stretched Example of signal conditioning for a Example of signal conditioning for a

strain gagestrain gage

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SummarySummary

Any analog quantity can be Any analog quantity can be represented by a binary number. represented by a binary number. Longer binary numbers provide Longer binary numbers provide higher resolution, which gives a more higher resolution, which gives a more accurate representation of the analog accurate representation of the analog quantity.quantity.

The binary-weighted D/A converter is The binary-weighted D/A converter is the simplest to construct, but it has the simplest to construct, but it has practical limitations in resolution practical limitations in resolution (number of input bits).(number of input bits).

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SummarySummary

Operational amplifiers are important Operational amplifiers are important building blocks in analog-to-digital (A/D) and building blocks in analog-to-digital (A/D) and digital-to-analog (D/A) converters. They digital-to-analog (D/A) converters. They provide a means for summing currents at provide a means for summing currents at the input and converting a current to a the input and converting a current to a voltage at the output of converter circuits.voltage at the output of converter circuits.

The R/2R ladder D/A converter uses only The R/2R ladder D/A converter uses only two different resistor values, no matter how two different resistor values, no matter how many binary input bits are included. This many binary input bits are included. This allows for very high resolution and ease of allows for very high resolution and ease of fabrication in integrated-circuit form.fabrication in integrated-circuit form.

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SummarySummary

The DAC0808 (or MC1408) IC is an The DAC0808 (or MC1408) IC is an 8-bit D/A converter that uses the 8-bit D/A converter that uses the R/2R ladder method of conversion. R/2R ladder method of conversion. It accepts 8 binary input bits and It accepts 8 binary input bits and outputs an equivalent analog outputs an equivalent analog current. Having 8 input bits means current. Having 8 input bits means that it can resolve up to 256 unique that it can resolve up to 256 unique binary values into equivalent analog binary values into equivalent analog values.values.

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SummarySummary

Applying an 8-bit counter to the Applying an 8-bit counter to the input of an 8-bit D/A converter will input of an 8-bit D/A converter will produce a 256-step sawtooth produce a 256-step sawtooth waveform at its output.waveform at its output.

The simplest way to build an analog-The simplest way to build an analog-to-digital (A/D) converter is to use to-digital (A/D) converter is to use the parallel encoding method. The the parallel encoding method. The disadvantage is that it is practical disadvantage is that it is practical only for low-resolution applications.only for low-resolution applications.

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SummarySummary

The counter-ramp A/D converter The counter-ramp A/D converter employs a counter, a D/A converter, employs a counter, a D/A converter, and a comparator to make its and a comparator to make its conversion. The counter counts conversion. The counter counts from zero up to a value that causes from zero up to a value that causes the D/A output to exceed the analog the D/A output to exceed the analog input value slightly. That binary input value slightly. That binary count is then output as the count is then output as the equivalent to the analog input.equivalent to the analog input.

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SummarySummary

The method of A/D conversion used The method of A/D conversion used most often is called successive most often is called successive approximation. In this method, approximation. In this method, successive bits are tested to see if they successive bits are tested to see if they contribute an equivalent analog value contribute an equivalent analog value that is greater than the analog input to that is greater than the analog input to be converted. If they do, they are be converted. If they do, they are returned to zero. After all bits are returned to zero. After all bits are tested, the ones that are left ON are tested, the ones that are left ON are used as the final digital equivalent to used as the final digital equivalent to the analog input.the analog input.

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SummarySummary

The NE5034 and the ADC0802 are The NE5034 and the ADC0802 are examples of A/D converter ICs. To examples of A/D converter ICs. To make a conversion, the start-make a conversion, the start-conversion pin is made LOW. When conversion pin is made LOW. When the conversion is completed the end-the conversion is completed the end-of-conversion pin goes LOW. Then of-conversion pin goes LOW. Then to read the digital output, the output to read the digital output, the output enable pin is made LOW.enable pin is made LOW.

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SummarySummary Data acquisition systems are used to Data acquisition systems are used to

read several different analog inputs, read several different analog inputs, respond to the values read, store the respond to the values read, store the results, and generate reports on the results, and generate reports on the information gathered.information gathered.

Transducers are devices that convert Transducers are devices that convert physical quantities such as heat, light, or physical quantities such as heat, light, or force into electrical quantities. Those force into electrical quantities. Those electrical quantities must then be electrical quantities must then be conditioned (or modified) before they conditioned (or modified) before they can be interpreted by a digital computer.can be interpreted by a digital computer.

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