Digital-to-Analog and Analog-to-Digital Conversion: Interface Part IV, Exams of Computer Science

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Digital-to-AnalogDigital-to-Analog

Analog-to-Digital Analog-to-Digital

Interface Part IV Interface Part IV Microprocessor Microprocessor

Data Handling SystemsData Handling Systems

 (^) Both data about the physical world and controlBoth data about the physical world and control signals sent to interact with the physical world signals sent to interact with the physical world are typically "analog" or continuously varying are typically "analog" or continuously varying quantities. quantities.  (^) In order to use the power of digital electronics,In order to use the power of digital electronics, one must convert from analog to digital form on one must convert from analog to digital form on the experimental measurement end and the experimental measurement end and convert from digital to analog form on the convert from digital to analog form on the control or output end of a laboratory system. control or output end of a laboratory system.

Digital-to-AnalogDigital-to-Analog Conversion Conversion [DAC][DAC]

Digital-to-Analog ConversionDigital-to-Analog Conversion

 (^) When data is in binary form, the 0's andWhen data is in binary form, the 0's and 1's may be of several forms such as the 1's may be of several forms such as the TTL form where the logic zero may be a TTL form where the logic zero may be a value up to 0.8 volts and the 1 may be a value up to 0.8 volts and the 1 may be a voltage from 2 to 5 volts. voltage from 2 to 5 volts.  (^) The data can be converted to cleanThe data can be converted to clean digital form using gates which are digital form using gates which are designed to be on or off depending on designed to be on or off depending on the value of the incoming signal. the value of the incoming signal.

Digital-to-Analog ConversionDigital-to-Analog Conversion

 2 Basic Approaches2 Basic Approaches

 (^) Weighted Summing AmplifierWeighted Summing Amplifier  (^) R-2R Network ApproachR-2R Network Approach

Weighted Sum DACWeighted Sum DAC

 (^) One way to achieve D/A conversion is toOne way to achieve D/A conversion is to use a summing amplifier. use a summing amplifier.  (^) This approach is not satisfactory for aThis approach is not satisfactory for a large number of bits because it requires large number of bits because it requires too much precision in the summing too much precision in the summing resistors. resistors.  (^) This problem is overcome in the R-2RThis problem is overcome in the R-2R network DAC. network DAC.

R-2R Ladder DACR-2R Ladder DAC

R-2R Ladder DACR-2R Ladder DAC

DAC0830/DAC0832DAC0830/DAC

8-Bit μP Compatible DAC 8-Bit μP Compatible DAC

 (^) An advanced CMOS/Si-Cr 8-bit multiplying DACAn advanced CMOS/Si-Cr 8-bit multiplying DAC designed to interface directly with the 8080, 8048, designed to interface directly with the 8080, 8048, 8085, Z80®, and other popular microprocessors. 8085, Z80®, and other popular microprocessors.  (^) A deposited silicon-chromium R-2R resistor ladderA deposited silicon-chromium R-2R resistor ladder network divides the reference current and provides the network divides the reference current and provides the circuit with excellent temperature tracking circuit with excellent temperature tracking characteristics (0.05% of Full Scale Range maximum characteristics (0.05% of Full Scale Range maximum linearity error over temperature). linearity error over temperature).

Typical ApplicationTypical Application

ADC Basic PrincipleADC Basic Principle

 (^) The basic principle of operation is to useThe basic principle of operation is to use the comparator principle to determine the comparator principle to determine whether or not to turn on a particular bit whether or not to turn on a particular bit of the binary number output. of the binary number output.  (^) It is typical for an ADC to use a digital-to-It is typical for an ADC to use a digital-to- analog converter (DAC) to determine one analog converter (DAC) to determine one of the inputs to the comparator. of the inputs to the comparator.

ADC Various ApproachesADC Various Approaches

 (^) 3 Basic Types3 Basic Types  (^) Digital-Ramp ADCDigital-Ramp ADC  (^) Successive Approximation ADCSuccessive Approximation ADC  (^) Flash ADCFlash ADC

Digital-Ramp ADCDigital-Ramp ADC

Digital-Ramp ADCDigital-Ramp ADC

 (^) The output of the DAC is applied to theThe output of the DAC is applied to the other terminal of the comparator. other terminal of the comparator.  (^) Since the output of the DAC is increasingSince the output of the DAC is increasing with the counter, it will trigger the with the counter, it will trigger the comparator at some point when its comparator at some point when its voltage exceeds the analog input. voltage exceeds the analog input.  (^) The transition of the comparator stopsThe transition of the comparator stops the binary counter, which at that point the binary counter, which at that point holds the digital value corresponding to holds the digital value corresponding to the analog voltage. the analog voltage.