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DA/AD CONVERTER. Digital-Analog Converter. DIGITAL-ANALOG CONVERTER. What is a DAC? Weighted Resistor DAC R-2R DAC Capacitive DAC DAC associated error Delta-Sigma DAC Conclusion. What is a DAC?.
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DIGITAL-ANALOG CONVERTER • What is a DAC? • Weighted Resistor DAC • R-2R DAC • Capacitive DAC • DAC associated error • Delta-Sigma DAC • Conclusion
What is a DAC? Digital-to-Analog Converter: An electronic device, often an integrated circuit, that converts a digital number into a corresponding analog voltage or current.
A/D Converter • In order to change an analog signal to digital, the input analog signal is sampled at a high rate of speed. • The amplitude at each of those sampled moments is converted into a number equivalent – this is called quantization. • These numbers are simply the combinations of the 0s and 1s used in computer language – this called encoding.
Digital to Analog (D/A, DAC, or D-to-A) Conversion • Converting discrete signals into discrete analog values that represent the magnitude of the input signal compared to a standard or reference voltage • The output of the DAC is discrete analog steps. • By increasing the resolution (number of bits), the step size is reduced, and the output approximates a continuous analog signal.
Weighting 23 22 21 20 Binary Digit 1 0 1 0 State +5V 0V +5V 0V DAC In an electronic circuit, a combination of high voltage (+5V) and low voltage (0V) is usually used to represent a binary number. For example, a binary number 1010 is represented by DACs are electronic circuits that convert digital, (usually binary) signals (for example, 1000100) to analog electrical quantities (usually voltage) directly related to the digitally encoded input number.
Block diagram of DAC DACs are used in many other applications, such as voice synthesizers, automatic test system, and process control actuator. In addition, they allow computers to communicate with the real (analog) world.
The two most popular types of resistive summing networks are: • Resistive divider circuit/Weighted binary resistance type • -Utilizies summing amplifier to form the weighted sum of all non-zero bits in the input • b)Ladder resistance (R-2R) type • -Maintains constant current through all branches (No voltage transients)
Resistive divider circuit/Weighted binary resistance Uses a summing amplifier circuit to generate output. Analysis uses KCL and Op-Amp properties to determine Vout.
Resistive divider circuit/Weighted binary resistance Binary Representation Rf = R Vo R 2R 4R 8R Most Significant Bit Least Significant Bit -VREF
Resistive divider circuit/Weighted binary resistance Disadvantages • Large number of resistors required for high bit DACs • High resistor values required for high bit DACs (32,768R for common 16-bit DACs) • Larger resistors cause more error in analog output
Only Input 4 is HIGH Only Input 3 is HIGH R-2R Ladder Used for Digital-to-analog converter!
Digital to Analog Converters-Common Applications-Digital Audio • CD Players • MP3 Players • Digital Telephone/Answering Machines 1 2 3 1. http://electronics.howstuffworks.com/cd.htm 2. http://accessories.us.dell.com/sna/sna.aspx?c=us&cs=19&l=en&s=dhs&~topic=odg_dj 3. http://www.toshiba.com/taistsd/pages/prd_dtc_digphones.html
Digital to Analog Converters-Common Applications-Function Generators • Digital Oscilloscopes • Digital Input • Analog Ouput 1 2 1. http://www.electrorent.com/products/search/General_Purpose_Oscilloscopes.html • Signal Generators • Sine wave generation • Square wave generation • Triangle wave generation • Random noise generation 2. http://www.bkprecision.com/power_supplies_supply_generators.htm
Digital to Analog Converters-Common Applications-Motor Controllers • Cruise Control • Valve Control • Motor Control 1 2 3 1. http://auto.howstuffworks.com/cruise-control.htm 2. http://www.emersonprocess.com/fisher/products/fieldvue/dvc/ 3. http://www.thermionics.com/smc.htm
Parameter of DAC For the selection of an IC DAC, there are several parameters that can determine the suitability of a particular device. Resolution The number of bits making up the input data word that will ultimately determine the output step voltage as a percentage of full-scale output voltage. Example: Calculate the resolution of an 8-bit DAC. Solution: Resolution = 8 bits Percentage resolution =
ANALOG-DIGITAL CONVERTER What is ADC(Analog to Digital Converter) Why ADC is needed Application of ADC A/D conversion process
ANALOG-DIGITAL CONVERTER What is ADC An electronic integrated circuit which transforms a signal from analog (continuous) to digital (discrete) form. Analog signals are directly measurable quantities. Digital signals only have two states. For digital computer, we refer to binary states, 0 and 1.
ANALOG-DIGITAL CONVERTER • A simple hypothetical A/D converter circuit with one analog input signal and three digital output lines with eight possible binary combinations: 000 to 111 • Shows the graph of digital output for FS V analog input • The following points can be summarized in the above process: • Maximum value this quantization process reaches is 7/8 V for a 1 V analog signal; includes 1/8 V an inherent error • 1/8 V (an inherent error) is also equal to the value of the Least Significant Bit (LSB) = 001. • Resolution of a converter is defined in terms of the number of discrete values it can produce; also expressed in the number of bits used for conversion or as 1/2n where n =number of bits • The value of the most significant bit (MSB) -100- is equal to ½ the voltage of the full-scale value of 1 V. • The value of the largest digital number 111 is equal to full-scale value minus the value of the LSB. • The quantization error can be reduced or the resolution can be improved by increasing the number of bits used for the conversion
ANALOG-DIGITAL CONVERTER Why ADC is needed Microprocessors can only perform complex processing on digitized signals. When signals are in digital form they are less susceptible to the deleterious effects of additive noise. ADC Provides a link between the analog world of transducers and the digital world of signal processing and data handling.
ANALOG-DIGITAL CONVERTER Application of ADC ADC are used virtually everywhere where an analog signal has to be processed, stored, or transported in digital form. Some examples of ADC usage are digital volt meters, cell phone, thermocouples, and digital oscilloscope. Microcontrollers commonly use 8, 10, 12, or 16 bit ADCs, our micro controller uses an 8 or 10 bit ADC.
ANALOG-DIGITAL CONVERTER Numerous methods are used for converting analog signals to digital form. Five most commonly used methods are listed below: • Staircase ramp • Successive approximation • Dual slope • Voltage to frequency • Parallel (or flash)
Staircase ramp/Counter/Digital Ramp Conversion from analog to digital form inherently involves comparator action where the value of the analog voltage at some point in time is compared with some standard. A common way to do that is to apply the analog voltage to one terminal of a comparator and trigger a binary counter which drives a DAC.
Staircase ramp/Counter/Digital Ramp • The clear pulse resets the counter to the zero. The counter then records in the binary form the number of pulses from clock line. The clock is a source of pulses equally spaced in time. Since the number of pulses counted increases as the input linearly with time, the binary word representing this count is used as the input of a DAC (Digital to Analog Converter) whose output is the stair case waveform • As long as the analog input VA is greater than VD, the comparator has an output which is high and the AND gate is open for transmission of the clock pulse to the counter. When VD exceeds VA the comparator output changes to low value and the AND gate is disabled. This stops the counting at the time when VA ≈ VD and the counter can be read out as the digital word representing the analog input voltage.
Staircase ramp/Counter/Digital Ramp • Advantages of Counter ADC • Very simple design • Cheap due to its simple design • Disadvantage of Counter ADC • Variable conversion time. • Slow operation
Successive approximation Illustration of 4-bit SAC with 1 volt step size
Successive approximation • Much faster than the digital ramp ADC because it uses digital logic to converge on the value closest to the input voltage. • A comparator and a DAC are used in the process.
