The signals are two types i.e. Analog & Digital signal. The information that is in real world exists in analog form, while the digital devices can only understand the digital signal in digital domain. The digital to analog converter (DAC) and analog to digital converter (ADC) are two type of converter. These two type of converter use in day to day life to convert the signal into each other. A digital to analog converter converts a digital input to analog output. Digital signal is a combination of group of binary bits 0 and 1. In this tutorial we are going to discuss the digital to analog converter.
What is Digital to Analog Converter (DAC)?
The digital to analog converter is an electronics device that convert digital input signal to analog output signal such as voltage or current. The digital signal is the combinations of the binary bits 0‘s and 1’s (or High & low voltage levels). These binary bit converts into analog signal such as voltage or current.
Need of Digital to Analog Converter (DAC)
In our real world all information exists in the analog form. So, why we convert them into digital form in the first place if we want to convert them back? Because the processing speed of digital signal is high and digital computer process a data in few second with accuracy. It save time and solve any complex data. But in real word we cannot understand the digital data. In order to understand the digital data we need a digital to analog converter.
Working of Digital to Analog Converter (DAC)
The digital signal is a group of the binary bits 0’s and 1’s. Each bit has its own weight corresponding to its position. The position weight is 2n where the n is the position of the bit & it start from 0, 1, 2…..
Convert binary number 10011 in to analog form;
(10011)2 = (1 x 24) + (0 x 23) + (0 x 22) + (1 x 21) + (1 x 20)
(10011)2 = 16 + 0 + 0 + 2 + 1
(10011)2 = 19
This shows how the binary digits convert in to analog form.
Types of Digital to Analog Converter (DAC)
There are two types of DAC
- Weighted Resistor DAC
- R-2R Ladder DAC
Weighted Resistor DAC
A weighted resistor DAC produces an analog output from the digital input. The analog signal is almost equal to digital signal, a binary weighted resistor DAC is also known as weighted resistor DAC. Below the figure shows the circuit diagram of a 3-bit binary weighted resistor DAC.
Binary Weighted Resistor D/A Converter Circuit
Let the 3-bit binary input bit is b2 b1 b0. Here b2 and b0 are denotes the Most Significant Bit (MSB) and Least Significant Bit (LSB) respectively. The digital switches above the figure shows connection of b2 b1 b0 to ground when ground input is equal to zero. Similarly, the digital switches are connected to – VR when the corresponding binary input bits are ‘1’. The non-inverting terminal of the op-amp is connected to the ground terminal and the inverting terminal of the op-amp is connected to the digital switches.
According to the virtual short concept the voltage of inverting input terminal is same to the non-inverting input terminal. So, the voltage of inverting terminal of Op-amp will be zero volts.
The equation of inverting input terminal is given below:
The above equation shows the output voltage equation of a 3-bit binary weighted resistor DAC.
The disadvantages of a binary weighted resistor DAC are given below
- Large resistance value required when increase inputs line.
- The value of large resistance is not accurate.
- It is difficult to design.
R-2R Ladder DAC
The R-2R Ladder DAC resolves the disadvantage of weighted resistance DAC. It is another type of digital to analog converter. When we giver digital input and obtained analog output. The circuit diagram of R-2R Ladder DAC is shown below.
Binary Ladder or R–2R Ladder D/A Converter Circuit
This type of conversion is more precise, easy to design and accurate. This circuit use combination R & 2R resistor in cascaded form which is shown in above figure. In this circuit we use only two type of resistor R & 2R. When we need zero to connected to GND switch, for 1’s the switch shifted to Vref . These switches are shifted by according to binary inputs.
Advantages of R-2R Ladder DAC;
- It uses only two types of resistors R & 2R.
- Easily scalable to any number of bits
- Output impedance is always R
Applications of Digital to Analog Converter
Digital to analog converter are use in all type of digital system because digital system are required less time and more accurate. Here some application of digital to analog converter is given below:
DAC are use in audio amplifier for produce DC voltage gain with microcontroller commands.
The video encoder system will process a video signal in digital system after processing it sends to DAC to convert it into analog format.
It is use in graphic controller to generate analog output such as Red, Green, Blue (RGB) signals to drive a display.