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**Digital-to-Analog Converters: **

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D/A conversion is the process of converting a value represented in digital code such as binary or BCD into a voltage or current which is proportional to the digital value. Fig represents the symbol of a typical 4 bit D/a converter. Each of the digital inputs A,B,C and D can assume a value 0 or 1, therefore there are 2^{4} = 16 possible combination of inputs. For each input number, D/A converter outputs a unique value of voltage. The analog output voltage Vout is proportional to the input binary number. So, Analog output = ( K *digital input) where K is proportionality factor and is constant for a given DAC.

**(Or)**

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Figure above represents a DAC using op-amp. The summing amplifier has four input resistances corresponding to four binary inputs D0,D1,D2 and D3.Switches are provided with each input. If a switch is open ,it indicates ‘0’And for closed switch it indicates ‘1’.

The output of the 4 bit DAC is : I_{in} = (V_{ref}/R)(D_{3}+2^{-1}D_{2}+2^{-2}D_{1}+2^{-3}D_{0}.

So the total voltage available at the output of the op-amp is the total of input voltage levels which represents the equivalent analog signals of the 4-bit digital input.