Digital to Analog Converter using 8 bit Weighted Resistors

Abstract -Giving 8 bit data as input to the summing amplifier and expecting output voltage to be analog . The circuit is found to be working satisfactorily .

I. INTRODUCTION

A digital to analog converter is a device which converts digital data to analog signal. Here the input is given in terms of 8 bit digital data to DAC and output is to be an analog voltage. Signals can be easily stored and transmitted in digital format but in order to be recognized by human or non-digital systems it should be converted to analog.

II. DESIGN AND WORKING

The WEIGHTED RESISTORS DAC circuit shown in fig.-1.If we give any analog signal in digital form of bits then number of bits is equal to the number of input weighted resistors used.As we are giving 8 bit data we will be having 8 weighted resistors in the circuit. All the 8 resistors are connected to the inverting terminal of opamp IC741 .

A switch is provided in between the input data and weighted resistors.Voltage reference is given to the 8 weighted resistors.A feedback resistor is connected between the inverting terminal and output terminal of the opamp.Vcc and ground are connected to pins of IC741 in accordamce to the datasheet.According to the value of feedback resistor used the value of weighted resistors is determined.

III. MATH

In general for an inverting opamp the output voltage is given as

V0 = Vref (-Rf/R1)

As we are using 8 bit data each bit is multiplied with corresponding voltage and finally summation of all these voltages gives the final analog output.

V0 = Vref*D0(-Rf/R0)+Vref*D1(-Rf/R1)+Vref*D2(-Rf/R2)+ Vref*D3(-Rf/R3)+Vref*D4(-Rf/R4)+Vref*D5(-Rf/R5)+ Vref*D6(-Rf/R6)+ Vref*D7(-Rf/R7).

By substituting the values of Rf and Ri where i = 0 to 7 we get the output voltage as

V0 = [(D0/2)+(D1/4)+(D2/8)+(D3/16)+(D4/32)+(D5/64)+

(D6/128)+ (D7/256)]*Vref.

Where Vref is taken as -5v.

IV. CIRCUIT DIAGRAM

A. Block diagram