Introduction to DSP

Engr. Hinesh Kumar Lecturer, I.B.T, LUMHS

Lecture Outline• Signal• Signal Classification• Signal Processing• Concept of Systems• DSP• Elements of DSP• Advantages of DSP• Limitations• Applications

Signal• A word ‘Signal’ comes from latin ‘Signum’

which means ‘Sign’.• “ A signal is a quantity or effect such as

current or voltage that can be varied in such a way as to convey information.” OR     

• “ A signal is defined as a mathematical function that conveys information about the state or behavior of a physical system.”

• Examples: electrical current, voltage, force, speed, speech, music, picture and video signals etc

Classification of Signal

Analog DigitalVS

Time Continuous Discrete

Amplitude Continuous Discrete

Analog Signal• An analog or analogue signal is any

continuous signal for which the time varying feature.

• An analog signal is a signal that exists at every instant of time

• A continuous signal is often referred to as continuous time or analog.

• The independent variable is a continuous variable

• Continuous signal can assume any value over a continuous range of numbers

Digital Signal• It is a special form of discrete time

signal which is discrete in time and amplitude.

• A digital signal is acquired by representing the sampled analog value into a finite set of values (quantization).

• These signals are called digital because the samples are represented by digits.

Signal Processing

Computer, Semiconduct and Information Science 1960’s-1970’s

Representation, transformation and manipulation

of signals and the information they contain.

Signal operation include:

(1) Transform, filter, inspection, spectrum analysis;

(2) Modulation and coding;

(3) Analog Signal Processing;

(4) Digital Signal Processing.

Basic Concept of SystemSystem

Device or technology of signal processing

Analog SystemSystem with analog input and output.

Digital SystemSystem with digital input and output.

Analog Signal

Acousticdomain

Electricdomain

Acousticdomain

Continuous-time System

Continuous-time system: the input and output signals

are continuous time

Programmable Analog System

Acousticdomain

Acousticdomain

Electricdomain

Digital domain

Discrete-time System

Discrete-time system has discrete-time input and output signals

Digital SystemsAcousticdomain

Electricaldomain

Electricaldomain

Acousticdomain

Digital domain

What is DSP?

a bit loudAnalog Computer

Digital Computer

ADC

DSP

DAC OUTPUT

1010 1001

a bit loud

What is DSP?• Converting a continuously changing waveform

(analog) into a series of discrete levels (digital).

• The analog waveform is sliced into equal segments and the waveform amplitude is measured in the middle of each segment

• The collection of measurements make up the digital representation of the waveform

DSP Basics• A basic DSP system is composed of:• An ADC providing digital samples of an analog

input• A Digital Processing system • A DAC converting processed samples to

analog output• Real-time signal processing: All processing

operation must be complete between two consecutive samples

Typical Architecture of DSP System

SensorSensor

ADCADC

Analog SignalConditioning

Analog SignalConditioning

Digital SignalConditioning

Digital SignalConditioning DSPDSP DACDAC

Analog Signal Processing

Digital Signal Processing

Block Diagram of DSP

Elements of DSP

1. An analog input

2. An analog filter,

3. An analog-to-digital conversion (ADC) unit,

4. A digital signal (DS) processor,

5. A digital-to-analog conversion (DAC) unit,

6. and a reconstruction (anti-image) filter.

I. Input Signal

• The analog input signal, which is continuous in

• time and amplitude.• It is the signal generated from some

transducer or some communication system.• Examples of such analog signals include

current, voltage, temperature, pressure.• It may be biomedical signal like ECG or EEG. • Generally it is analog in nature. It is denoted

by x(t).

II. Anti Aliasing Filter

• This is basically a low pass filter.

• It is used for the following purposes. It removes the high frequency noise contained in input signal.

As the name indicates, it avoids aliasing effect. That means it is used to band limit the signal.

III. Analog to Digital Converter (ADC)

• The band-limited signal at the output of

the analog filter is then sampled and

converted into the digital signal, which

is discrete both in time and in amplitude.

• This is required because digital signal

processor accepts the signal which is

digital in nature.

IV. Digital Signal Processor

• It processes input signal digitally. • In a simple language processing of input

signal means modifying the signal as per requirement.

• It consists of lowpass, highpass, and bandpass digital filtering, or other algorithms for different applications.

• DS processor is a special type of digital computer consists of , a microprocessor, or an advanced microcontroller; and can be implemented using software in general.

V. Digital to Analog Signal (DAC)

• The DAC unit, converts the output of the

digital signal processor into an analog

output signal.

• The signal is continuous in time and

discrete in amplitude.

VI. Reconstruction Filter

• Output signal of DAC is an analog, that

means it is a continuous signal.

• It may contain high frequency components

which are unwanted.

• To remove these components,

reconstruction filter is used.

Advantages of DSP1. Versatility

Digital systems can be reprogrammed for multiple applications ( where programmable DSP chips are used). Moreover, digital systems can be ported to different hardware

2. Repeatability Digital systems can be easily

duplicated. These systems do not depend upon component tolerances and temperature.

Advantages of DSP3. Simplicity:

It is easy to built any digital system as compared to an analog one.4. Accuracy:

To design an analog system, analog components like resistors, capacitors and inductors are used. The tolerance of these components reduce accuracy of the system. While in case of DSP; much better accuracy is obtained.

Advantages of DSP5. Remote Processing

Analog signals are difficult to store because of problems like noise and distortion. While digital signal can be easily stored on storage media like magnetic tapes, disks etc. Thus as compared to analog signals digital signals can be easily transposed. So remote processing of digital signal can be done easily.

Advantages of DSP6. Implementation of algorithms: The mathematical processing algorithms can be easily implemented in case of digital signal processing.But such algorithms are difficult to implement in case of analog signals.7. Easy Up gradations:

Because of the use of software, digital signal processing systems can be easily upgraded as compared to analog systems.

Advantages of DSP8. Compatibility:

In case of digital systems, generally all applications needs standard hardware. Thus operation of DSP system is mainly dependent on software. Hence universal compatibility is possible as compared to analog systems.9. Cheaper:

In many applications, the digital systems are comparatively cheaper than analog systems.

Limitations of DSP1. System Complexity:

DSP system needs use of converters

like ADC and DAC.

This increases the system complexity

compared to analog systems. Similarly in

many applications, the time required for this

conversion is more.

Limitations of DSP• Bandwidth Limitation:

In case of DSP system, if input signal is having wide bandwidth then it demands for high speed ADC. This is because to avoid aliasing effect, the sampling rate should be at least twice the bandwidth. Thus such signals require fast digital signal processors. But always there is practical limitation in the speed of processors and ADC.

Limitations of DSP3. Power Consumption:

A typical digital signal processing chip contains more than four lakh transistors.Thus power dissipation is more in DSP systems as compared to analog systems

4. For small applications digital signal processing systems are expensive as compared to analog systems

ApplicationsIMAGE PROCESSING

Pattern recognition

Robotic vision

Image enhancement

Satellite weather map

animation

IMAGE PROCESSING

Pattern recognition

Robotic vision

Image enhancement

Satellite weather map

animation

INSTRUMENTATION & CONTROL

Spectrum analysis

Position and rate control

Noise reduction

Data compression

INSTRUMENTATION & CONTROL

Spectrum analysis

Position and rate control

Noise reduction

Data compressionSPEECH & AUDIO

Speech recognition

Speech synthesis

Text to speech

digital audio

SPEECH & AUDIO

Speech recognition

Speech synthesis

Text to speech

digital audio

MILITARY

Secure communication

Radar processing

Sonar processing

Missile guidance

MILITARY

Secure communication

Radar processing

Sonar processing

Missile guidance

TELECOMMUNICATION

Echo cancellation

Adaptive equalization

Video conferencing

data communication

TELECOMMUNICATION

Echo cancellation

Adaptive equalization

Video conferencing

data communicationBiomedical

Patient monitoring

Scanners

ECG (Electrocardiograph)

X-ray storage/enhancement

Biomedical

Patient monitoring

Scanners

ECG (Electrocardiograph)

X-ray storage/enhancement

Consumer applications

digital, cellar mobile phones

universal mobile telecommunication system

digital television

digital camera

internet music, phones and video

digital answer machines, fax and modems

voice mail system

interactive entertainment systems

Consumer applications

digital, cellar mobile phones

universal mobile telecommunication system

digital television

digital camera

internet music, phones and video

digital answer machines, fax and modems

voice mail system

interactive entertainment systems