Digital to Analog Converters

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Digital to Analog Converters

Digital to Analog Converter (DAC) converts a digital enter sign into an analog output sign. The digital sign is represented with a binary code, which is a mixture of bits Zero and 1. This chapter offers with Digital to Analog Converters intimately.

The block diagram of DAC is proven within the following determine −

Digital to Analog Converter

A Digital to Analog Converter (DAC) consists of quite a few binary inputs and a single output. Normally, the variety of binary inputs of a DAC will probably be an influence of two.

Sorts of DACs

There are two sorts of DACs

  • Weighted Resistor DAC
  • R-2R Ladder DAC

This part discusses about these two varieties of DACs intimately −

Weighted Resistor DAC

A weighted resistor DAC produces an analog output, which is sort of equal to the digital (binary) enter through the use of binary weighted resistors within the inverting adder circuit. Briefly, a binary weighted resistor DAC known as as weighted resistor DAC.

The circuit diagram of a 3-bit binary weighted resistor DAC is proven within the following determine −

Binary Weighted Resistors

Recall that the bits of a binary quantity can have solely one of many two values. i.e., both Zero or 1. Let the 3-bit binary enter is b2b1b0b2b1b0. Right here, the bits b2b2 and b0b0 denote the Most Vital Bit (MSB) and Least Vital Bit (LSB) respectively.

The digital switches proven within the above determine will probably be linked to floor, when the corresponding enter bits are equal to ‘0’. Equally, the digital switches proven within the above determine will probably be linked to the damaging reference voltage, VR−VR when the corresponding enter bits are equal to ‘1’.

Within the above circuit, the non-inverting enter terminal of an op-amp is linked to floor. Meaning zero volts is utilized on the non-inverting enter terminal of op-amp.

Based on the digital brief idea, the voltage on the inverting enter terminal of opamp is identical as that of the voltage current at its non-inverting enter terminal. So, the voltage on the inverting enter terminal’s node will probably be zero volts.

The nodal equation on the inverting enter terminal’s node is:

0+VRb220R+0+VRb121R+0+VRb022R+0V0Rf=00+VRb220R+0+VRb121R+0+VRb022R+0−V0Rf=0
=>V0Rf=VRb220R+VRb121R+VRb022R=>V0Rf=VRb220R+VRb121R+VRb022R
=>V0=VRRfR{b220+b121+b022}=>V0=VRRfR{b220+b121+b022}

Substituting, R=2RfR=2Rf in above equation.

=>V0=VRRf2Rf{b220+b121+b022}=>V0=VRRf2Rf{b220+b121+b022}
=>V0=VR2{b220+b121+b022}=>V0=VR2{b220+b121+b022}

The above equation represents the output voltage equation of a 3-bit binary weighted resistor DAC. Because the variety of bits are three within the binary (digital) enter, we’ll get seven attainable values of output voltage by various the binary enter from 000 to 111 for a hard and fast reference voltage, VRVR.

We are able to write the generalized output voltage equation of an N-bit binary weighted resistor DAC as proven beneath primarily based on the output voltage equation of a 3-bit binary weighted resistor DAC.

=>V0=VR2{bN120+bN221+....+b02N1}=>V0=VR2{bN−120+bN−221+….+b02N−1}

The disadvantages of a binary weighted resistor DAC are as follows −

  • The distinction between the resistance values similar to LSB & MSB will improve because the variety of bits current within the digital enter will increase.
  • It’s troublesome to design extra correct resistors because the variety of bits current within the digital enter will increase.

R-2R Ladder DAC

The R-2R Ladder DAC overcomes the disadvantages of a binary weighted resistor DAC. Because the identify suggests, R-2R Ladder DAC produces an analog output, which is sort of equal to the digital (binary) enter through the use of a R-2R ladder community within the inverting adder circuit.

Thecircuit diagramof a 3-bit R-2R Ladder DAC is proven within the following determine −

Ladder DAC

Recall that the bits of a binary quantity can have solely one of many two values. i.e., both Zero or 1. Let the 3-bit binary enter is b2b1b0b2b1b0. Right here, the bits b2b2 and b0b0 denote the Most Vital Bit (MSB) and Least Vital Bit (LSB) respectively.

The digital switches proven within the above determine will probably be linked to floor, when the corresponding enter bits are equal to ‘0’. Equally, the digital switches proven in above determine will probably be linked to the damaging reference voltage, VR−VR when the corresponding enter bits are equal to ‘1’.

It’s troublesome to get the generalized output voltage equation of a R-2R Ladder DAC. However, we will discover the analog output voltage values of R-2R Ladder DAC for particular person binary enter combos simply.

The benefits of a R-2R Ladder DAC are as follows −

  • R-2R Ladder DAC comprises solely two values of resistor: R and 2R. So, it’s straightforward to pick out and design extra correct resistors.
  • If extra variety of bits are current within the digital enter, then we’ve to incorporate required variety of R-2R sections moreover.

Because of the above benefits, R-2R Ladder DAC is preferable over binary weighted resistor DAC.