GUHA PO TSE R INTRODUCTION After completing this chapter, you should be able to: + Define or explain the following terms: signal, deterministic signal, non-deterministic Understand how to classify a signal based on RHuHUenRas he tineverani tet Know the difference between analog, discrete and digital signal. Compare the difference between analog and digital signal processor. Compare the features of different commercial digital signal processors. Know the overview of the application areas of DSP. 1.1 INTRODUCTION In recent years, there is a tremendous development in the fabrication of microchips for the design of efficient digital system and this has led to a new discipline known as Digital Signal Processing (SP). Digital signal processing is a technique of performing mathematical operations on signals, represented as sequences of samples using coding on a microprocessor oF digital signal processor chip, Digital signal processing is becoming an important modern tool in the fields like speech and audio processing, biomedical, communication, acoustics, radar, geophysics, robotics and control applications. This chapter covers types of signals, types of processing systems and commercial digital signal processors. The chapter concludes with overview of application areas of DSP. 1.2. SIGNAL CLASSIFICATION nformation and plays an important role in our daily life. Examples of signals that we encounter frequently in our daily life are speech and physiological signals Examples of physiological signals are Electrocardiogram (ECG) and Electroencephalogram (EEG) signals. ECG signal provides information about the condition of the heart and BEG signal provides information about the condition of the brain. Speech, ECG and BEG signals are examples of information bearing signals as a function of time. 1 Signal is a means that conveys i2 Monerw Dicirat SIGNAL ProcessinG __ i y that varies with time, spa Signal is defined as any physical quantity that ; PACE OF any ote E such as distance, position, temperature, pressure, etc 9 Signals are classified into two types: + Deterministic signal + Non-deterministic signal Deterministic signals are those that ean be described by mathematical mode) ay deterministic signal are those that eannot be described by mathematical model andar in terms of probabilities or with the help of their statistical properties. Dependit characteristics of the time variable, signals can be classified into following types: + Continuous time signal * Discrete time signal * Digital signal 1.2.1 Continuous Time Signal Almost all the signals generated from various sources in the nature are continuous time sions, In continuous time signals both amplitude and time are continuous variables. Continuous sme signals are also called analog signals. Electrocardio, (@) ECG signals (b) EEG signals (©) Speech signals Figure 11 Examples of continuous time signals. 1.2.2 Discrete Time Signal (1) 7, 1 =0,1,2,3,.. ‘Then analog signal and discrete signal are related by (1) = x(n.) n=0,1,2,3,.. (2) aIwmoouerion _3 . x(n) eS eae aaa oa on Figure 1.2 Sampling of continuous to discrete time signal. ‘This means x() is represented as samples at 0, 7,, 27, 3T,,.. or discrete signal is defined only atn= 0,1, 2,3, 4,... Sampling time 7, is the time difference between any two adjacent samples, which is determined by the highest frequency of the input signal. The sampling frequency is at least twice the highest frequency of the signal. =O fe (1.3) 1.2.3 Digital Signal The signals represented in microprocessor or in digital signal processors are digital signals. ‘These signals are represented by a function x(n). In digital signal, the sampled value of the analog ‘magnitude is converted into a binary number. The digitization process consists of two main stages: sampling the signal and quantization. Quantization converts the sampled amplitude into binary code words. The conversion of analog signal to digital form is performed by analog to digital (A/D) converter and digital signal is converted back to analog by digital to analog (D/A) converter. In the digital signal both time and amplitude are represented by 1 bit (binary), 3 bits (octal), 4 bits (hexadecimal), 8 bits, 16 bits, 32 bits or 64 bits. 1.3 SIGNAL PROCESSING SYSTEMS Till now we were discussing about signals and their classification. In this section we will discuss about signal processing systems. System is defined as a physical device that performs an operation on a signal. System is defined mathematically as an operator that maps an input sequence into an ‘output sequence. The systems can be classified into following types: * Analog signal processing system * Digital signal processing system 1.3.1 Analog Signal Processing System As discussed in Section 1.2, almost all the signals generated from various sources are analog in nature, Originally signal processing was done on analog or continuous time signals. The system used to process analog signal is known as analog signal processing system. The block diagram of an analog processing system is shown in Figure 1.3.Analog signal ae Analog signal i Analog signal |__ en | processor a x [erases | Figure 1.3. Analog signal processing system is to process the input analog sig, she function of analog signal processor is to p ol i ; 18Nal BY funy Ba tion, amplification, filtering, current to voltage conversion, volt; as attenuation, 4.3.2 Digital Signal Processing System Until the late 1950s digital computers were not commercially available. After the de,q microprocessor, analog processing systems were replaced by digital process The concepts are very simple. The analog signals are converted to digital signals by» digital converter (A/D). The signal is sampled in time at a constant rate and analog magring converted into a binary number with an analog to digital converter. Digital Signals are proc. 4 by using microprocessors or digital signal processors. After processing, digital oun processor are converted into an equivalent analog signal by a digital to analog Converter (Dy) Figure 1.4 represents the block diagram of a typical digital signal processing system ‘Opmen Analog Digital Digital + ts ; f " ; signal signal | Analog to signal | Microprocessor | Signal Digital to | signal yp | Sisital converter [— >] or Sp *| analog converter | ——> x@ x(n) x(n) x) Figure 1.4. Digital signal processing system. Digital signal processing enjoys several advantages over analog signal process significant of these are the following: i. The mos * Digital systems can be made accurate, by selecting word length according to the required accuracy. * Easy storage facility and less expensive, + In digital systems Output does not vary due to environmental factors. * They are reprogrammable, functions can be changed by changing the program. * Implementation of mathematical operations, which i difficult or even impossible using a2 signal processor. * Security can be provided through hardware or by coding techniques. The processor may be a gene The microprocessor architecture is i ae ‘on a Real tine digital signal processing is performing operations op transformations of sist! processor in synchronization with events occurring sin the physical system and with fimé ESSE A Rios sia iialurrooueTin In real time digital signal processing applications require, mathematical operations to be performed quickly. Both software and hardware must be extremely efficient to accomplish this. The digital signal processor is optimized to accomplish these tasks fast enough to maintain real time operations. The DSP’s differ from general-purpose microprocessors and microcontrollers in that they are specially designed to perform single cycle arithmetic operations and accumulations They support mathematical functions specifically intended for processing digital signals. The current trends in technology seem to indicate the possibility through that distinction between a DSP and the microprocessor will be gone. The Microprocessors are now becoming more and more sophisticated that some of them are now equipped with true DSP capabilities. 1.4 COMMERCIAL DIGITAL SIGNAL PROCESSORS A. Oppenheim and R. Schafer first published the textbook Digital Signal Processing. In 1979, Intel announced the first digital signal processor chip Intel 2920. In 1990, Intel released 1960, which is used in DSP applications and in multimedia. In 1982, DSP chips were designed by NEC MPD 7720 and by Texas instruments TMS 32010. These chips were capable of 16 bits integer arithmetic operations, with the speed of 33.3 and 5 Million Instructions Per Second (MIPS) and had limited Random Access Memory (RAM), Read Only Memory (ROM) and Input/Output (UO) devices. The salient features of some of the DSP processors are summarized in Table 1.1 ‘Table 1.1 Commercial DSP Processors ‘Vendor Processor Famil Arithmetic Type Data Width _ Speed(MIPS) AT and T DSP16xx Fixed 16 70.0 DSP32xx Floating. 32 20.0 Motorola DSPS600x Fixed 24 40.0 DSP561xx Fixed 16 30.0 DSPS63xx Fixed 24 80.0 DSP96002 Floating. 32 20.0 Analog Devices ADSP-21xx Fixed 16 33.3 ADSP-210xx Floating 32 40.0 ‘Texas Instruments TMS320CIx Fixed 16 88 TMS320C2x Fixed 16 12.5 TMS320C2xx Fixed 16 40.0 TMS320C3x Floating 32 25.0 TMS320C4x Floating 32 30.0 TMS320C5x Fixed 16 50.0 TMS320C54xx, Fixed 16 50.0 TMS320C6713 Floating 32 1800.0 1.5 OVERVIEW OF APPLICATION AREAS OF DSP A wide variety of commercial DSP systems are the core of many new and emerging digital products. DSP systems are becoming more powerful because of their speed and lower cost. In this section we will discuss few application areas.y 6 __Mooenw DiciTaL SIGNAL PROCESSING Spectrum anal, + Biomedical ysis peal hearing aid Motor control Patient monitoring Noise reduction Ultrasound equipment Process control + Image processing X-ray Magabtie Resonance Imaging (MRI). Image enhancement ECG and EEG analysis Image analysis + Audio and speech processing Image compression Audio mixing Image recognition Speech recognition Animation Speech enhancement * Military Speech synthesis Secure communication Text to speech Radar processing Speaker verification Navigation + Telecommunication Sonar processing Data communication Missile guidance Echo cancellation + Consumer applications FAX Digital television Cellular telephone Digital camera Video-conferencing Mobile phones Speakerphones Voicemail systems + Instrumentation and control Sound recording Robot control Toys 1.6 SUMMARY In this chapter, the meaning of DSP has been explained. Classification of signals and types of final processing systems are discussed. Commercial DSP processors and areas of applications have been discussed. Multiple Choice Questions 1. Deterministic signal is (a) Random signal (b) Completely specified function of time (c) Partly specified function of time (@) Specified by statistical properties 2. Non-deterministic signal can be modelled by (a) Integral equation (b) Difference equation (c) Differential equation (d) Statistical parametersiz InrropucTion 3. The features in which DSP is superior to microprocessor (a) Low cost (b) Low power consumption (©) Real time 1/0 capability (d) None of the above 4, Analog signal and discrete signal are related by (a) x =x(nT,) (b) x) = x(n) (©) x@) =x@T,.) (d) x(4) = x(n) 5. Advantages of analog signal processing systems are (a) Easy storage facility (b) Less expensive (©) Accurate (d) None of the above Review Questions « Distinguish between deterministic and non-deterministic signals. Explain the differences between analog, discrete and digital signals. . Distinguish analog signal processing system and digital signal processing system with diagrams. 4. What is a real time digital signal processing system? . List few application areas of DSP. ye a