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Digital - to - Analog & Analog - to - Digital Converters | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE) PDF Download

Digital - to - Analog And Analog - to - Digital converters 

A/D AND D/A CONVERTERS
Digital - to - Analog converters The input to a D/A converter is an N-bit binary signal. The analog output voltage Vo of an N-bit straight binary D/A converter is related to the digital input by the equation.
Digital - to - Analog & Analog - to - Digital Converters | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

where, K = Proportionality factor.
bn = 1 if the nth bit of the digital input is 1. = 0 if the nth of the digital input is 0.
Two Types of Commonly Used D/A Converters.

1. Weighted-resistor D/A converter and
2. R-2 R ladder D/A converter.

 Digital - to - Analog & Analog - to - Digital Converters | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

Resister for MSB = R Resister for LSB = 2N–1.R
Digital - to - Analog & Analog - to - Digital Converters | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

 Example : 4 bit D/A, V (1) = 1V, RF = 8R. Obtain analog output for 0101?

 Digital - to - Analog & Analog - to - Digital Converters | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

D/A Performance Characteristics 1. FSV (full scale voltage): It represents maximum output voltage for the DA converter and is obtained when all bits of digital input are 1.
The output for any bit is e0 = VR/2n
where n = no. of bits.
FSV = VR [1 - (1/2n)]

 2. Resolution

 Digital - to - Analog & Analog - to - Digital Converters | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

3. Ccuracy: It is the error between the actual output of DA converter to the expected or theoretical output and expressed as percentage of FSV.
If the converter has an accuracy of ± 0.1% for FSV of 10 V, the minimum error for any output voltage is [(10/100) × 0.1] = 10 mV Ideally the accuracy should be = ± [1/2]1 LSB.

4. Monotonicity: It means that the output increase for an increase of input or decreases for decrease of input. The output should not decrease for increase of input. 5. Settling Time: It is the time taken by DA converter to settle within + [1/2] LSB of its final value.

Major component of the binary weighted resistance DAC:
a) a weighted resistor network, R to 2n-1 R
b) n switches, one for each bit applied bit input.
c) A reference voltage Vref
d) A summing element Defects:

The chief detect of weighted binary DAC is that the resistor values increases in multiples of 2.

If the value of MSB is 2 KW. then for a 10 bit, the value for LSB is 29. 2K = 1.024 MW.
It is difficult to obtain high precision at very high values. It is also difficult to fabricate high value resistance by integrated circuit methods. This is over come by the ladder type DA converter.

 R-2R ladder Network In this, only two values of resistors are used.

Digital - to - Analog & Analog - to - Digital Converters | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)
Digital - to - Analog & Analog - to - Digital Converters | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

The number of resistor required for an N-bit ladder D/A converter is 2N in the case of R-2R ladder D/A converter whereas it is only N is the case of weighted-resister D/A converter.

Analog-to-digital converters :Types of ADC 

1. Parallel-comparator/flash/simultaneous A/D 

  • Simplest in concept and fastest conversion time. 
  • Disadvantages are rapid increase in the number of comparators with the number of bits, (2N-1) comparators are required for an N-bit converter.

 Digital - to - Analog & Analog - to - Digital Converters | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

2. Successive Approximation A/D converter 

  • For N-bit converter, the number of clock pulses required would be N. 
  • Slow than the parallel-comparator A/D Offset voltage = 1/2 LSB – 0.5

Digital - to - Analog & Analog - to - Digital Converters | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

3. Count ing A /D conver t er The maximum number of clock pulse required conversion is 2N for an N-bit A/D converter. This conveter is slower than the other two converters discussed earlier.

4. Dual-slope A/D converters Major component of a dual-slope A/D converter.
1. An integrator
2. A comparator
3. A binary counter
4. A switch driver.

Conversion time of ADC

1. Counter of Ramp type ADC

 
Digital - to - Analog & Analog - to - Digital Converters | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

2. Successive approximation ADC
Digital - to - Analog & Analog - to - Digital Converters | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

3. Dual slope ADC Slowest conversion time 4. Flash ADC Fastest conversion time tc = (1/f) 

  • Conversion time independent from no. of bit. 
  • The number of Comparator = 2n–1 where f = clock frequency.

Aperture Time Aperture time is called the maximum allowable conversion time tc.

 Digital - to - Analog & Analog - to - Digital Converters | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

where, w = angular frequency of signal applied
n = number of bit for ADC
ta = aperture time.

The document Digital - to - Analog & Analog - to - Digital Converters | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE) is a part of the Electrical Engineering (EE) Course Electrical Engineering SSC JE (Technical).
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FAQs on Digital - to - Analog & Analog - to - Digital Converters - Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

1. What is the purpose of a digital-to-analog converter (DAC)?
Ans. A digital-to-analog converter is used to convert digital signals into analog signals. It takes a digital input signal (usually in binary form) and generates a corresponding continuous analog output signal.
2. How does a digital-to-analog converter work?
Ans. A digital-to-analog converter works by using a reference voltage and a series of resistors to convert the binary input signal into an analog output voltage. The input signal is typically a binary number that represents the amplitude of the analog signal. The converter converts each bit of the binary number into a corresponding voltage level, which is then combined to generate the analog output signal.
3. What is the purpose of an analog-to-digital converter (ADC)?
Ans. An analog-to-digital converter is used to convert analog signals into digital signals. It takes a continuous analog input signal and converts it into a discrete digital representation, typically in binary form. This allows the analog signal to be processed and manipulated digitally by computers and other digital devices.
4. How does an analog-to-digital converter work?
Ans. An analog-to-digital converter works by sampling the analog input signal at regular intervals and quantizing each sample into a digital value. The analog signal is first sampled, meaning that its amplitude is measured at discrete time intervals. Then, the measured amplitude is quantized, which means it is assigned a digital value based on its amplitude relative to a reference voltage. This process is repeated for each sample, generating a stream of digital values that represents the original analog signal.
5. What are the applications of digital-to-analog and analog-to-digital converters?
Ans. Digital-to-analog and analog-to-digital converters are used in a wide range of applications. Some common applications include audio processing (such as in music players and sound systems), telecommunications (such as in modems and digital telephony), data acquisition (such as in sensors and measurement devices), and control systems (such as in robotics and automation). These converters play a crucial role in enabling the interface between digital and analog systems.
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