DAC | Digital to Analog Converter Using R-2R Ladder Network and 741 Op Amp With Simulated Output Waveform

What is DAC? A Digital to analog converter (DAC) is used to get analog voltage corresponding to input digital data. Data in Binary digital form can be converted to an analog form by using an R-2R ladder (binary weighted resistor) network and a summing amplifier. It is more common and practical.

Actually different types of digital to analog converter ICs are available commercially based on this same principle. Note that, the R-2R ladder network is built by a set of resistors of two values.

Learn how to build a Digital to Analog converter using the simple technique explained in detail. Here is the circuit and output simulated waveform of Digital to Analog Converter Using R-2R Ladder Network. It uses an op-amp (741) as a summing amplifier.

Circuit Diagram of Digital to Analog Converter Using R-2R DAC and 741 Op Amp

Components Required log Digital to Analog Converter Using Op Amp

1. Resistors (1KΩx4, 2KΩx5)
2. 741 Op Amp
3. 7493 Counter IC

Working Principle of R-2R ladder network DAC

• R-2R weighted resistor ladder network uses only 2 set of resistors: R and 2R. If you want to build a very precise DAC circuit, be precise while choosing the values of the resistors. They should exactly match the R/2R ratio.
• This is a 4 bit DAC network. Consider the digital data D₃D₂D₁D₀= 0001 is applied to the DAC.
• Then the Thevenin equivalent circuit reduction is shown below.

• V_ref is nothing but is the input binary value reference voltage. That is for binary 1, V_ref=5V. And for binary 0, V_ref=0V.
• For 0001 only D₀=V_ref. All other inputs are at 0V i.e. they can be treated as ground.
• So finally V_ref/16 volt is appearing as the input to op amp. This value gets multiplied by the gain of op amp circuit “–(R_f/R_i)”.
• If we proceed in this manner (Thevenin equivalent reduction), we will get

• Note that you can build a DAC with any number of bits you want. For that, simply rnlarge the resistor network by adding more R-2R resistor branches.
• In this circuit the 7493 IC is simply provides digital inputs to the DAC. It is a counter IC and not an integral part of the DAC circuit. You can apply any combinations of binary inputs to D₃D₂D₁D₀

Output waveform of DAC circuit

Components pin out

i-St@r Lab

Conclusion

Practical signals, whether audio, video, or photo, are all analog in nature. But digital circuits and devices we use are yet to grasp and analyze them directly in analog. They convert the signals to digital for processing. Thus in the output terminals, our required signals are to be retrieved. As a result, Digital to Analog Converter Using R-2R and ap-amp has this much significance.