PSK/QPSK MODULATOR+HIGH PASS FILTER B.E. PROJECT REPORT ADC(12811) Prepared by Salman Khaliq Bajwa (3746) Ali Arsalan (4377) Mohammad Ghazanfar (4965) Advisor Asstt. Professor, Muhammad Abbas Lab Engineer Mr. Zia ul Haq College of Engineering PAF-Karachi Institute of Economics & Technology Karachi
DEDICATION This report is dedicated to My Parents, Teachers & Friends, Whose love, affection and support helped me in bringing my work to this level ofaccomplishments; I am also thankful to them for their unconditional support and encouragement to pursue my interests, even when the interest went beyond the boundaries of field and scope. Without their support and kindness this work would not have been possible.
ACKNOWLEDEMENT Praise to Allah the most beneficent and the most mercifulWe are grateful to our project advisor Mr. Abbas, for enlightening us with his preciousknowledge and vast experience to benefit us in the future. We also like to thank to our teachersand lab assistants, lab engineer especially Mr. Zia ul Haq for their assistance and support.We would also thank with all gratitude and depth of our hearts to our parents who helped usnot only financially but with integrity too and support us in all our hardships. Finally our sincerethanks to our institute PAF-KIET, College of Engineering, for providing us the opportunity togave us the strength to undertake this research.Special thanks to all our fellows and friends who lend us a hand throughout this project.We pray this effort may prove to be the beginning of new era, a era in which Science andTechnology may make great progress in Pakistan and Pakistan may become a part of thedeveloped nations.Thank you.
Objective:The main objective of this project is to design and construct a PSK/QPSK modulator.Description:Before going to the PSK modulation, we first need to understand what is modulation and whydo we need it?Modulation:It is the process of putting information on to a high frequency carrier for transmission.Baseband signal Modulator Modulated SignalWhy Modulation?In simple terms, modulation is required to transmit signals from variuos sources simultaneously over acommon channel by means of multiplexing.For ex., the bandwidth of speech signals is 3.3KHz.,andtransmitting N no.of speech signals simultaneously each of BW 3.3KHz causes interference.Hence,toovercome this problem, each speech signal is modulated onto one of N carriers of frequencies60KHz,64KHz,68KHz etc...There are 3 major reasons :1) To use much more smaller antennas.2) Channel allocation for todays thousands of todays users.3) For better noise immunity.What is Phase-shift keying (PSK) modulation?Phase-shift keying (PSK) is a digital modulation scheme that conveys data by changing, ormodulating, the phase of a reference signal (the carrier wave).
All convey data by changing some aspect of a base signal, the carrier wa (usually a sinusoid), inresponse to a data signal. In the case of PSK, the phase is changed to represent the data signal.There are two fundamental ways of utilizing the phase of a signal in this way: By viewing the phase itself as conveying the information, in which case the demodulator must have a reference signal to compare the received signals phase against; or By viewing the change in the phase as conveying information — differential schemes, some of which do not need a reference carrier (to a certain extent).A convenient way to represent PSK schemes is on a constellation diagram. This shows thepoints in the complex plane where, in this context, the real and imaginary axes are termed thein-phase and quadrature axes respectively due to their 90° separation. Such a representationon perpendicular axes lends itself to straightforward implementation. The amplitude of eachpoint along the in-phase axis is used to modulate a cosine (or sine) wave and the amplitudealong the quadrature axis to modulate a sine (or cosine) wave.
In PSK, the constellation points chosen are usually positioned with uniform angular spacingaround a circle. This gives maximum phase-separation between adjacent points and thus thebest immunity to corruption. They are positioned on a circle so that they can all be transmittedwith the same energy. In this way, the moduli of the complex numbers they represent will bethe same and thus so will the amplitudes needed for the cosine and sine waves. Two commonexamples are "binary phase-shift keying" (BPSK) which uses two phases, and "quadraturephase-shift keying" (QPSK) which uses four phases, although any number of phases may beused. Since the data to be conveyed are usually binary, the PSK scheme is usually designed withthe number of constellation points being a power of 2.What is Quadrature phase-shift keying (QPSK)?Sometimes this is known as quaternary PSK, quadriphase PSK, 4-PSK, or 4-QAM. (Although theroot concepts of QPSK and 4-QAM are different, the resulting modulated radio waves areexactly the same.) QPSK uses four points on the constellation diagram, equispaced around acircle. With four phases, QPSK can encode two bits per symbol, shown in the diagram with graycoding to minimize the bit error rate (BER) — sometimes misperceived as twice the BER ofBPSK.The mathematical analysis shows that QPSK can be used either to double the data ratecompared with a BPSK system while maintaining the same bandwidth of the signal, or tomaintain the data-rate of BPSK but halving the bandwidth needed. In this latter case, the BER ofQPSK is exactly the same as the BER of BPSK - and deciding differently is a common confusionwhen considering or describing QPSK.
Given that radio communication channels are allocated by agencies such as the FederalCommunication Commission giving a prescribed (maximum) bandwidth, the advantage of QPSKover BPSK becomes evident: QPSK transmits twice the data rate in a given bandwidth comparedto BPSK - at the same BER. The engineering penalty that is paid is that QPSK transmitters andreceivers are more complicated than the ones for BPSK. However, with modern electronicstechnology, the penalty in cost is very moderate.Process:
Circuit:We had used KL-94006 modulator circuit in order to construct a PSK/QPSK modulator circuit.The circuit diagram of the KL94006 modulator is given below;
Schematic:Components: ICL 8038 WAVEFORM GENERATOR 4052 DIFFERENTIAL 4-CHANNEL ANALOG MULTIPLEXERS/DEMULTIPLEXERS 4070 EXCLUSIVE OR 4094 8-STAGE SHIFT-AND-STORE BUS REGISTER 4520 DUAL BINARY COUNTER LF356 SINGLE J-FET OPERATIONAL AMPLIFIERS TL084 GENERAL PURPOSEJ-FET QUAD OPERATIONAL AMPLIFIERS CD4096 Micropower Voltage Reference Diode Resistors Capacitors
Project 2: High Pass FilterObjective:The main objective of this project is to design and understand the basics and working of filtersespecially high pass filters.Description:High pass filters remove signals below the selected frequency, and pass the signals above theselected frequency unaffected (hence the term high pass). High pass filters have a slopemeasured in the amount of signal reduction (in dB) per frequency octave. Typically these valuesare in multiples of 6 dB/Oct. At the exact selected frequency of the high pass filter the signalreduction is usually -3 dB, however this can change based on filter design. A high pass filter isuseful for removing low frequency rumble, unwanted vocal plosives, and dc offsets. This isSimple high pass Filter perform filter especial tall frequency can change only. By use IC 741, bethe integrated circuit op-amp very the circuit helps to are high frequency Filter model to besimple. By from the circuit will let 750 HZ frequencies s go up change more well, 60HZfrequencies are or lower. By friends can change the value RC for filter the frequency that canwant which can see the detail has followed circuit picture yes.Circuit: