# Digital to Analog Converters (D/A)

john August 10, 2017 15 Comments

A D/A Converter is used when the binary output from a digital system is to be converted into its equivalent analog voltage or current.

The binary output will be a sequence of 1’s and 0’s. Thus they ma be difficult to follow. But, a D/A converter help the user to interpret easily.

Basically, a D/A converter have an op-amp. It can be classified into 2 types. They are

## 1. Digital to Analog Converter using Binary-Weighted Resistors

Digital-to-Analog Converter Circuit – Binary-Weighted Resistors Method

We know that, a 4-bit converter will have 24韦德体育投注网是什么,韦德体育app = 16 combinations of output. Thus, a corresponding 16 outputs of analog will also be present for the binary inputs.

#### Working

The circuit is basically working as a current to voltage converter.

• b0 is closed

It will be connected directly  to the +5V.

Thus, voltage across R = 5V

Current through R = 5V/10kohm = 0.5mA

Current through feedback resistor, Rf = 0.5mA (Since, Input bias current, IB韦德体育投注网是什么,韦德体育app is negligible)

Thus, output voltage = -(1kohm)*(0.5mA) = -0.5V

• b1 is closed, b0 is open

R/2 will be connected to the positive supply of the +5V.

Current through R will become twice the value of current (1mA) to flow through Rf.

Thus, output voltage also doubles.

• b0 and b1 are closed

Thus, according to the position (ON/OFF) of the switches (bo-b3), the corresponding “binary-weighted” currents will be obtained in the input resistor. The current through Rf will be the sum of these currents. This overall current is then converted to its proportional output voltage. Naturally, the output will be maximum if the switches (b0-b3) are closed

The graph with the analog outputs versus possible combinations of inputs is shown below.

## 2. Digital to Analog Converter with R and 2R Resistors

A D/A converter with R and 2R resistors is shown in the figure below. As in the binary-weighted resistors method, the binary inputs are simulated by the switches (b0-b3), and the output is proportional to the binary inputs. Binary inputs can be either in the HIGH (+5V) or LOW (0V) state. Let b3 be the most significant bit and thus is connected to the +5V and all the other switchs are connected to the ground.

Digital to Analog Converter with R and 2R Resistors

Thus, according to Thevenin’s equivalent resistance, RTH,

RTH = [{[(2RII2R + R)} II2R] + R}II2R] + R = 2R = 20kOhms.

The resultant circuit is shown below.

Digital to Analog Converter with R and 2R Resistors – Resultant Circuit

Graph is given below.

Digital to Analog Converter with R and 2R Resistors – Graph

In the figure shown above, the negative input is at virtual ground, therefore the current through RTH=0.

Current through 2R connected to +5V = 5V/20kohm = 0.25 mA

The current will be the same as that in Rf.

Vo = 韦德体育投注网是什么,韦德体育app-(20kohm)*(0.25mA) = -5V

V0 韦德体育投注网是什么,韦德体育app = -Rf (b3/2R+b2/4R+b1/8R+b0/16R)

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• klemens
November 7, 2016

any one to help out with full details on the components within the DAC circuit diagram and a view of layout

• April 10, 2015

韦德体育投注网是什么,韦德体育appexcellent thanks

• POOJA
April 15, 2014

can we use 741 in place of 351??

• Seetharaman
April 16, 2014

You can use TL071, which is an FET input opamp of equivalent characteristic to LF351.

• Ambika
April 19, 2015

韦德体育投注网是什么,韦德体育appyes, of course….741 is also acceptable..

• POOJA
April 12, 2014

韦德体育投注网是什么,韦德体育appHi… Your post helped me to understand the concept of DAC.

• November 16, 2013

韦德体育投注网是什么,韦德体育appit require the types of of electronic switch used in dac

• June 15, 2013

Hello there! Good post! Please inform us when I will see a follow up!

• k.vijaykumar
October 23, 2012