EASP PROJECT REPORT

ADC and DAC using MATLAB

Introduction:

Analog to Digital Converter:

Real world is always analog. Analog

to Digital Converters(ADC) provides an interface between the real world and the

digital world by converting the analog signals to digital signals.

Digital to Analog Converter:

Digital to Analog Converters(DAC)

takes a digital code as its input and produces an analog voltage or current as

its output. This analog output is proportional to the digital input.

Flow chart:

The structure of

our project is given as below.

Code and Description:

1. Analog to Digital Converter:

The input analog signal is generated

for 1000 samples using the function ‘gensumsin’. Then a random noise is

generated and added to the original analog signal. The plots of analog signal

with and without noise is presented below:

The next step would be to sample the

acquired analog signal. Sampling is the reduction of a continuous-time signal

to a discrete-time signal. A sample is a value or set of values at a point in

time and/or space. Sampling is done to convert the continuous signal into its

discrete form. It is done before quantization so that each sample can be

represented by 8 digits corresponding to 128 levels of quantization. The code

presented below was used to do the same.

The results obtained from sampling

the analog signals (with and without noise) is shown below:

The final step of ADC would be to

quantize the sampled signals obtained from sampling. Quantization is

done to replace each real number with an approximation from a finite set of

discrete values (levels), which is necessary for storage and processing by

numerical methods. The code dedicated to this process is as shown below:

The

output plots (shown below) obtained from this process is the output of the

Analog to Digital Converter.

We then calculated the SNR ratio for

the ADC outputs (with and without noise) to compare and analyze the results. Signal

to Noise Ratio is a calculated value that represents the ratio of rms signal to

rms noise.

The SNR value obtained for the

output with noise was approximately equal to 18dB whereas the SNR value

calculated for the output without noise was approximately equal to 50dB. If a

signal has greater value of SNR, it is said to be good signal. From this, we

can interpret that the output without noise was the better case of the two.

2. Digital

to Analog Converter:

The output of Analog to Digital

converter is then used as the input of the Digital to Analog converter.

We use low pass filtering method to

obtain the original analog signals. The signal is passed through a

properly designed filter that reconstructs the original analog wave form from

its digitally coded counterpart. Here,

we have used the fir filter of type 1 to achieve the results. This filter was chosen because of its simple and easy

implementation, it does not distort its phase when it delays the input signal

and can be easily designed to be ‘linear phase’.

The code implemented for the filtering process is as

presented below:

The input of DAC after passing through

the filter gives us the original analog signal as its output. The output of the

Digital to Analog Converter for with and without noise are as shown below:

The comparison of the original

Analog signal with noise and the obtained output of the DAC with noise is as

shown below:

From the above plots, it is obvious

that the output of the DAC holds most of the data of the original input analog

signal.

Frequency spectrum analysis was then

performed on the output of DAC. The Fourier transform converts the time

function into a sum of sine waves of different frequencies, each of which

represents a frequency component. The spectrum of frequency components is the

frequency domain representation of the signal. The code below was used to

perform the same.

The output plots of the spectrum analysis

is as presented below:

From the above plots, we can

interpret that both the sides of the frequency spectrum (positive and negative

sides) of the output signal with noise shows more distortions than the output

without noise.

Conclusion:

The analog signal obtained as the

output of Digital to Analog Converter was very close to the original analog

signal when performed experimentally. However, practically, retaining all the

data of the original signal is not possible. It usually incurs some loss of

data.

By,

Subiksha Muralidharan,

Sundara Rajan Manoharan.