DESIGNING OF PRE-AMPLIFIER AND GUI FOR Nd:YAG LASERAProject ReportSubmitted byPRIYANKA & JYOTI YADAVB.TECH. (Electronics and Communication)NATIONAL INSTITUTE OF TECHNOLOGY, KURUKSHETRA

JULY-2014LASER SCIENCE AND TECHNOLOGY CENTER (DRDO) DEFENCE RESEARCH AND DEVELOPMENT ORGANIZATIONMINISTRY OF DEFENCE METCALFE HOUSE DELHI 110054

CERTIFICATE

This is to certify that Ms. Priyanka and Ms. Jyoti Yadav, students of B.TECH (Electronics and Communication) third year, of NATIONAL INSTITUTE OF TECHNOLOGY, KURUKSHETRA has completed their project on the subject DESIGNING OF PRE-AMPLIFIER AND GUI FOR ND:YAG LASER under my guidance at Laser Science and Technology Centre, Defence Research and Development Organization (DRDO), Ministry of Defence, Metcalfe House, Delhi from 13th June 2014 to 24th July 2014.

Mr. Mukesh Kumar Jindal Dr. Anil K. RazdanScientist D Scientist G(Project Guide) (Head, LIDAR & BD division)

CONTENTS

ACKNOWLEDGEMENT ABSTRACT LIST OF FIGURES1. DESCRIPTION OF LIDAR SYSTEM1.1 LIDAR system details 1.2 Laser source and its properties1.3 Block diagram of laser system2. DESIGN OF PRE-AMPLIFIER 2.1 Introduction to multisim 2.2 General description of AD829 2.3 Experimental Setup3.INTRODUCTION TO LABVIEW SOFTWARE 3.1 Introduction3.2 Importance & capabilities of Lab VIEW3.3 Lab VIEW for data acquisition and analysis 3.4 Working With RS232 3.5 Interfacing Through LabVIEW

REFERENCES

ACKNOWLEDGEMENT

We are highly grateful to Shri Hari Babu Shrivastav , Director, LASTEC for allowing us to do this project work. It is truly a matter of great pleasure for us to express our sincere thanks and gratitude to Dr. Anil K. Razdan, Sc-G, Head, LIDAR and BD Division, LASTEC for his supervision and encouragement throughout the course of this project. We are highly obliged to Dr. S. Veerabuthiran, Sc-D, LASTEC for his guidance, kind concern and encouragement throughout this work. We are immensely indebted to Mr. Mukesh Kumar Jindal, Sc-D, LASTEC for the invaluable help that he rendered to us at every step of this project. Our special thanks to Mr.Vikas Sagar, Senior Technical Assistant B for his guidance and support throughout the project. We also take this opportunity to thank all scientists, research and administrative staffs of LASTEC for their cooperation during this project. Our thanks are also due to the staff of the Library, LASTEC for their help and cooperation.

ABSTRACT

LIDAR is the acronym for LIght Detection And Ranging. LIDAR is an active remote sensing device, which uses laser as a transmitter. Basic principle of lidar is that when a laser pulse is transmitted in the atmosphere by a laser source (Nd: YAG), a fraction of transmitted pulse is scattered back to the receiver by the molecules and particles (aerosols) in the atmosphere, which act as distributed scatterers. The received radiation is collected by an optical system (telescope) and is focused on to an optical detector. The electrical signal from detector is amplified using a preamplifier with respect to time, digitized, stored, and analysed using a computer. Continuous scanning of the atmosphere using lidar is very much needed for air pollution monitoring and detection of toxic gases accidentally released into the atmosphere. Design of Preamplifier and GUI for Nd: YAG laser is carried out in this project report. The Preamplifier for detection channel:The return signal produces a fast decaying current pulse at the output of the detector. The gain provided by the detector is not sufficient to amplify the Lidar return echo from the lower altitude. It has to be further amplified and converted into a voltage pulse for further processing using the preamplifier. The current pulse is automatically converted into a fast transient voltage pulse by the input impedance of the preamplifier in DC coupled mode.The GUI for Nd: YAG laser was developed using LABVIEW software. In this Start and Stop functions are implemented for Nd:YAG laser.

LIST OF FIGURESChapter 1- Description of Lidar System Fig 1.1- Schematic Diagram of Lidar systemChapter 2- Design of pre-amplifier Fig 2.1- Design of amplifier in multisim Fig 2.2- Input and Output WaveformsChapter 3- Development of GUI using LabVIEW Fig.3.1- LabVIEW Block Diagram Example Fig 3.2- LabVIEW Computing Targets Fig.3.3-GUI for Nd: YAG laser Chapter 1Description of Lidar system

LIDAR is the acronym for LIght Detection And Ranging. It is a powerful technique for the study of atmospheric structure and dynamics. The spatial and temporal variability of minor constituents of the atmosphere such as aerosols, dusts, clouds, water vapour, wind speed and temperature structure of the upper atmosphere can be studied using Lidar. In this chapter, basic principle of Lidar, types of laser used for the remote sensing of the atmosphere and mechanism of scattering/absorption processes when the laser interacts with the atmosphere are discussed.1.1 IntroductionThe remote sensing of the atmosphere can be classified broadly into two categories, namely passive remote sensing and active remote sensing. In passive remote sensing methods, the source is beyond the control of the observer, e.g. radiometer, photometer, spectrometer, etc. In active remote sensing methods, the source can be controlled by the observer e.g. Lidar, radar, sonar, etc. Active remote sensing requires an additional source of Electromagnetic radiation, which sends light out from the system into the scene to be collected with or without any ambient light. Electromagnetic radiations use spectrum like radio waves (in RADAR), microwave radiation, visible, as well as ultraviolet light. An aspect of active sensing is the prospect of receiving more information than in passive collection .So LIDAR is an active remote sensing device using laser light as the source of transmission.

1.2 Lasers for Remote Sensing

In the field of remote sensing, lasers play an important role due to their inherent capability of generating well-collimated beams with outstanding characteristics in high coherence, monochromatic, and directivity. Laser remote sensing techniques provide powerful tools for scientific studies of the atmosphere, environmental monitoring, and measurement of air quality parameters, remote sensing of oceans and rivers, remote assessment of vegetation, etc. Developments in laser technology such as second harmonic generation, high power, compact diode pumped solid-state lasers, and tuneable solid state lasers, etc. have opened new possibilities of laser remote sensing to explore the Earths atmosphere. One of the newest Lidar innovations known as Volume Imaging Lidar is a technique that finds use in many strategic areas apart from its applications in studying the in homogeneities in the atmosphere. Laser remote sensing of the atmosphere is generally referred as LIDAR. Similar to radar, in Lidar, a laser pulse is sent into the atmosphere and is used as a spectroscopic probe of its physical state and chemical composition. The emitted laser beam interacts with the atmospheric constituents causing alterations in the intensity, polarization, and wavelength of the backscattered light. From the measurements of these parameters of the received backscattered light, one can deduce the properties of the atmosphere and its constituents. The Lidar allows range resolved measurement to obtain a vertical profile of the atmospheric parameters. The distance of the scattering medium can be deduced with high accuracy from the time delay of the return signal. Lidar systems can be operated in the wavelength range extending from the ultraviolet to the infrared (UV to IR) by using different types of lasers. Using the techniques of scattering, absorption, resonance and fluorescence, Lidar can measure solid particulate matter such as aerosols, species of very low concentrations such as ozone, water vapour and metal atoms such as Na, K, etc. Lidar measurements of the Rayleigh scattering from a neutral atmosphere can be used to determine neutral density, pressure, temperature, and wind speed. Studies in the past decade have demonstrated the reliability of Rayleigh Lidar technique for measuring the temperature and dynamics of the atmosphere in the altitude region of 30-80 km. Visibility measurements can be used for air traffic control in case of foggy or cloudy atmosphere.

1.3 Laser Source and its Properties:The Laser is the most critical part of any Lidar System. Lasers which are capable of emitting pulses of high peak power, narrow band width and short duration with low beam diversions are ideal for probing the environment. Lasers used for these applications should be capable of operating at high repetition rate when the return signal is very weak and for studying the short-term scientific phenomenon. The importance of some of these laser parameters are explained below: 1.3.1 Pulse Energy:The higher the laser pulse energy, the better the signal to noise ratio for a given range, as the backscattered signal (power) will be higher.1.3.2 Pulse Length:This sets a limit to the range resolution. If the pulse length is , the pulse illuminates a finite length c of the atmosphere at any instant, where c is the speed of light. But since the received energy must travel a 2-way path, the atmospheric length from which signals can be received at any time is c/2. For example, a 10 ns pulse length can provide a 1.5 m range resolution (taking c = 3 108 m/s). For atmospheric measurements, a pulse length of a few tens of nanoseconds will be generally required.1.3.3 Beam Quality:The lower the beam divergence, the better it is. A lower beam divergence enables us to keep the field-of-view of the receiving telescope low so that the amount of background noise is reduced. A beam divergence of 1m rad or less is required for the output beam. Beam divergence can be improved by expanding the beam with a telescope and this also makes the beam more eye-safe. Beam expansion is required particularly for higher altitude (above 70 km) studies in order to improve the signal-to-noise ratio as well as to increase the spatial resolution in the horizontal plane.1.3.4 Pulse Repetition Frequency (PRF):A high repetition rate speeds the acquisition of the required number of pulses for averaging. Some of the atmospheric measurements need high repetition rate to study fast varying phenomena or parameter with periodicity of few seconds to few minutes. Typical repetition rates used in atmospheric Lidars vary from few Hz to few tens of Hz.

1.4 Advantages of Laser over Other Techniques: It provides better imaging. It has very less diffraction so it provides better collimation, better spatial resolution and better imaging. Better angular range and Doppler resolution. Narrow Spectrum and high Coherence. Wavelength tenability. Efficient control of Polarization. Backscattering available from aerosol particles.

1.5 Basic Principle of LIDAR

A fraction of the light in the transmitted pulse is scattered back to the receiver by the molecules and particles (aerosols) in the atmosphere, which act as distributed scatterers. The received radiation is collected by an optical system (telescope) and is focused on to the cathode of a optical detector preferably a photo multiplier tube (PMT). The electrical signal from PMT is amplified, digitized, stored, and analyzed using a computer. Since the transmitted pulse has a finite duration , it illuminates a finite geometrical length c (c is the velocity of light) of the atmosphere at any instant. However, since the received energy must travel a two-way path, the atmospheric length (or range increment) from which signals received at any time is c/2. This method allows a range resolved measurement. All the backscattered photons arriving in the time range /2 are stored in one range bin. A typical range resolution of 75 m requires a 500 ns range bin. A single profile is recorded for each laser shot. The single shot profiles are added together at each altitude to build up a sufficient signal at the corresponding altitude. For example if a laser fires 1000 shots at the rate of 10 pulses per second, then time required to build up a single statistically significant profile is 100 s.

1.6 Lasers Used In Lidar Systems

LaserWavelength (m)Energy(J)PRF(Hz)Range(km)Parameter studied

Ruby

Nd: YAG

CO2

CO

Dye Lasers0.694

1.064

9 11

5-6.5

0.35-1.062-3

1

1-10

Not used for pulsed applications0.1-200.5

10

1-50

Not used for pulsed applications10-100Up to 40

Up to 80

Up to 50

Up to 15

Up to 90Aerosols, volcanic ashAerosols, dust, cloudsH2O, CO2, NH4 etcCO, Hg, CO2 etc

Temperature, pressure.

Table 1.1 Lasers Used In Lidar Systems

Here for the purpose of experiment ND: YAG (1064nm) is used.Nd:YAG(neodymium-doped yttrium aluminium garnet;Nd:Y3Al5O12) is acrystalthat is used as alasing mediumforsolid-state lasers. Thedopant, triply ionizedneodymium, Nd(III), typically replaces a small fraction (1%) of theyttriumions in the host crystal structure of the yttrium aluminium garnet(YAG), since the two ions are of similar size. It is the neodymium ion which provides the lasing activity in the crystal, in the same fashion as red chromium ion in ruby lasers.

Nd:YAGlasers areoptically pumpedusing aflashtubeorlaser diodes. These are one of the most common types of laser, and are used for many different applications. Nd:YAG lasers typically emit light with awavelengthof 1064nm, in the infrared.However, there are also transitions near 940, 1120, 1320, and 1440nm. Nd:YAG lasers operate in both pulsed and continuous mode. Pulsed Nd:YAG lasers are typically operated in the so-calledQ-switchingmode: An optical switch is inserted in the laser cavity waiting for a maximumpopulation inversionin the neodymium ions before it opens. Then the light wave can run through the cavity, depopulating the excited laser medium at maximum population inversion. In this Q-switched mode, output powers of 250 megawatts and pulse durations of 10 to 25 nanoseconds have been achieved.The high-intensity pulses may be efficientlyfrequency doubledto generate laser light at 532nm, or higher harmonics at 355 and 266nm.The amount of the neodymiumdopantin the material varies according to its use. Forcontinuous waveoutput, the doping is significantly lower than for pulsed lasers. The lightly doped CW rods can be optically distinguished by being less colored, almost white, while higher-doped rods are pink-purplish. Other common host materials for neodymium are: YLF (yttrium lithium fluoride, 1047 and 1053nm), YVO4(yttrium orthovanadate, 1064nm), andglass. A particular host material is chosen in order to obtain a desired combination of optical, mechanical, and thermal properties.

1.7 Types of Lidar1.Atmospheric Backscattering LidarThis is the most common type of Lidar. It is employed to measure the particulate matter such as ashes, dust, droplets, ice crystals, aerosols etc. in the atmosphere. High Energy Laser Pulses are sent into the investigated region and the returned signal is detected and analyzed. The term backscattering refers to the case where the scattered radiation is at an angle 180 to the incident radiation, the Lidar configuration being mono-static with the transmitter and receiver allocated.Mie scattering is applicable when the average size of the scatterer is of the same order as that of the wavelength of incident radiations. In this technique, the laser radiations is elastically scattered from the molecules or aerosols with no change in the wavelength.2.Raman LidarThis is used to measure the temperature profiles in the atmosphere, which is based on the rotational Raman Structure, which depend strongly on temperature. It has mainly been applied to major atmospheric gases i.e. N2, O2, H2O or toxic gases (SO2, NO, CO, H2S, CH4) in stacks and other sites where the concentrations are high, the measurements have to be carried out as close range to have enough return signals.Raman scattering: In this technique, the laser radiations is inelastically scattered from the molecules, and the return signal is shifted in frequency. The difference in frequency between the incident and return radiations is equal to the characteristic vibrational frequency of the molecule. 3. Doppler LidarThis type of Lidar is based on the well-known Doppler Effect in which one observes a shift in wavelength of the return signal due to a relative motion between the sensor and the object. This technique provides wind velocity and direction based on the Doppler shifts of the backscattered signal. Since the speeds of molecules and aerosols are very different, it is possible to separate their relative contribution in the returned signal.4. Fluorescence LidarIn this technique, the laser is tuned to the absorption line of an atmospheric compound, which is excited and subsequently decays after 1s-1ns by emitting light at a wavelength equal or longer than the excitation wavelength. Laser-Induced Fluorescence technique has been employed to identify various biological warfare (BW) agents and also to discriminate between biological and non biological threatening clouds through the use of lasers in the visible and UV bands. This type of Lidar has been employed to major mesospheric atoms (Li, Na, K, Ca) arising from meteorites. Another important species that has been measured by Fluorescence Lidar is the OH radical.5. Differential Absorption Lidar (DIAL)This technique has been extensively used to monitor air pollutants and gases in the atmosphere. This technique uses two wavelengths to measure the concentration of the given species. In the scheme, two close by wavelengths are employed: one wavelength, , is centered on a line within the absorption band of molecules of interest (this wavelength is also called the on line wavelength (on); the second wavelength (off) is detuned to the wing of online wavelength .Ratio of the return signals at these wavelength determines the concentration of the molecules of interest due to differential absorption 6. Backscattering LidarThe Backscattering LIDAR system is based on the elastic scattering due to suspended particulate matters in the atmosphere. It has been widely used for characterization of aerosol properties, clouds, visibility measurements etc. Backscattering LIDARs are capable of measuring the aerosol distribution in both space and time, and provide valuable information in identifying boundary layer height, pollution layers, and sources of pollution. Furthermore, its ability to characterize clouds and its technical simplicity and reliability make Backscattering LIDAR a useful tool for atmospheric research. Several scattering/absorption mechanisms are present when the laser energy interacts with the atmosphere. The term backscattering refers to the case where the scattered radiation is at an angle 180 to the incident radiation, the Lidar configuration being mono-static with the transmitter and receiver collocated.

1.8 Components of Lidar System

Lidar is based on the principle of transmitting a laser pulse into the atmosphere, which interacts with air molecules, aerosols (particles whose size varies between 0.01 and 50 m) and clouds. The backscattered radiation is collected by suitable optical telescope and focused onto a detector. The data acquisition is carried out in the analog mode or photon counting mode. Further, the return signal is integrated to generate a signal versus range profile.

Laser TransmitterThe typical Nd: YAG laser is the main transmitting source in the Lidar system. Its fundamental wavelength is 1064 nm in the near infrared. To operate the system in visible and UV, the second, third and fourth harmonics of the fundamental wavelength are used. The operating wavelengths for these harmonics are 532 nm, 355 nm and 266 nm. The pulse width of the laser is 10ns and its pulse repetition frequency (PRF) is 10 Hz with typical energy of 350Mj.

ReceiverIn general the receiver system consists of a 500 or 300 mm Cassegrain telescope depending upon the altitude coverage. Using a post optics system, the received signal is delivered to the optical detector. The detector channel receives the entire signal covering from near ground to far region. The interference filter pass bandwidth of 3 nm centered on the laser line wavelength reduces the system background noise almost to a negligible value.

DetectorThe purpose of the detector is to convert electromagnetic energy into an electric signal that can be analyzed. Detectors are classified into thermal types and quantum types. Thermal detectors use infrared energy as heat and their photosensitivity is independent of the wavelength. Thermal detectors do not require cooling but have disadvantages like slow response time and low detection capability. In contrast, quantum detectors offer higher detection performance and faster response but their photosensitivity depends on wavelength. In general quantum detectors must be cooled for accurate measurement, except for the detectors used in the near infrared region. A number of different semiconductors are also in common use as optical detectors in Lidar. These include Silicon APD's in the visible, near ultraviolet and near infrared, germanium and indium gallium arsenide in near infrared and indium antimonide, indium arsenide in the mid-infrared region.

Preamplifier for detection channelThe return signal produces a fast decaying current pulse at the output of the detector. The gain provided by the detector is not sufficient to amplify the Lidar return echo from the lower altitude. It has to be further amplified and converted into a voltage pulse for further processing using the preamplifier. The current pulse is automatically converted into a fast transient voltage pulse by the input impedance of the preamplifier in DC coupled mode.

Data Acquisition SystemThe preamplifier signal from the detection channel is recorded using the appropriate digitizer boards with suitable sampling rates. The digitized samples are initially stored in the onboard memory of the digitizer and then transferred to the hard disk for further processing. The backscattering signal due to Mie scattering and Rayleigh scattering is collected in various channels using PMT detectors

1.9 Block Diagram of Lidar System:

It is shown in figure 1.1. The receiver is an optical telescope. The laser pulses are sent into the atmosphere. A fraction of the transmitted pulse is scattered back to the receiver by the molecules and particles (Aerosols) in the atmosphere, which act as distributed reflector. This method allows a range resolved measurement. The received radiation is focused on to the photo detector which may be photo multiplier tube, which provided a current or voltage proportional to the light intensity. It comprises of one photocathode and anode and a series of electrodes between these two with increasing potential called dynodes. The photo electrons generated at the cathode hit the first dynode and a number of secondary electrons are generated. These hit the second dynode and so on, generating secondary electrons at each stage. The total number of electrons keeps on multiplying at each stage.The multiplicative factor being between 4 & 10. The secondary electrons from the last dynode are collected at the anode. The electrical signal from the PMT is amplified, digitized and analysed using a computer. The LIDAR controller provides the accurate timing and control pulses for the operation of the different channels while simultaneously providing synchronization.Fig 1.1: Schematic Diagram of Lidar system

Chapter 2Design of Pre-amplifier

The preamplifier for detection channel was designed using multisim .The return signal produces a fast decaying current pulse at the output of the detector. The gain provided by the detector is not sufficient to amplify the Lidar return echo from the lower altitude. It has to be further amplified and converted into a voltage pulse for further processing using the preamplifier. The current pulse is automatically converted into a fast transient voltage pulse by the input impedance of the preamplifier in DC coupled mode.The amplifier was designed using AD829 that is a high speed , low noise amplifier.

2.1 Introduction to MultiSim

MultiSim is an interactive circuit simulation package that allows the student to view their circuit in schematic form while measuring the different parameters of the circuit. The ability to create a schematic quickly and then analyze the circuit through simulation makes MultiSim a wonderful tool to help students understand the concepts covered in the study of electronics. Multisim is the schematic capture and simulation application of National Instruments Circuit Design Suite, a suite of EDA (Electronics Design Automation) tools that helps you carry out the major steps in the circuit design flow. Multisim is designed for schematic entry, simulation, and exporting to downstage steps, such as PCB layout. Schematic capture is the first stage in developing your design. This is where you choose the components you want to use, place them on the workspace in the desired position and orientation, wire them together, and otherwise prepare your design. You can modify component properties, orient your design on a grid, add text and a title block, add subcircuits and buses, and control the color of the workspace background, components and wires. Depending on your version of Multisim, you can open as many designs as you want at the same time. Each design appears in its own window. The active window is, as in other Windows applications, the window with the highlighted title bar. You can use the Window menu to move from design to design, or just click on the tab at the bottom of the workspace that corresponds to the design you want to see.Multisim includes a number of virtual instruments that you can use to measure the behavior of your designs. These instruments are set, used and read just like their real-world equivalents. In addition to the standard instruments that come with Multisim, you can create your own custom instruments using LabVIEW, a graphical development environment for creating flexible and scalable test, measurement, and control applications. Virtual instruments have two views-the instrument icon you attach to your circuit, and the front panel, where you set the instruments controls. You can show or hide the face by double-clicking on the instrument's icon. The front panels are always displayed on top of the main workspace so that they are not hidden. You can place the front panels wherever you wish on your desktop. When you save your design, the front panel locations and show/hide status are stored. Any data contained in the instruments is saved, up to a preset maximum size. The instruments icon indicates how the instrument is connected to the circuit. Once the instrument is connected, a black dot appears inside the terminal input/output indicators on the front panel.

2.2 Operational Amplifier

The term operational amplifier or "op-amp" refers to a class of high-gain DC coupled amplifiers with two inputs and a single output.In this configuration, an op-amp produces an output potential (relative to circuit ground) that is typically hundreds of thousands of times larger than the potential difference between its input terminals. The op-amp is one type ofdifferential amplifier.The amplifier's differential inputs consist of a non-inverting input (+) with voltageV+and an inverting input () with voltageV; ideally the op-amp amplifies only the difference in voltage between the two, which is called thedifferential input voltage. The output voltage of the op-ampVoutis given by the equation: Vout = Aol (V+ - V-) whereAOLis theopen-loopgain of the amplifier (the term "open-loop" refers to the absence of a feedback loop from the output to the input). If predictable operation is desired, negative feedback is used, by applying a portion of the output voltage to the inverting input. Theclosed loopfeedback greatly reduces the gain of the circuit. When negative feedback is used, the circuit's overall gain and response becomes determined mostly by the feedback network, rather than by the op-amp characteristics. In negative feedback two configurations are there: Inverting and Non-inverting. In our Design, we have used non-inverting configuration.

2.3 Non-inverting amplifier configuration

Fig.2.1 Non-inverting amplifier configuration

In the non-inverting amplifier on the right, the presence of negative feedback via the voltage dividerRf,Rgdetermines theclosed-loop gainACL=Vout/Vin.To analyze this circuit , the following assumptions are made: When an op-amp operates in linear (i.e., not saturated) mode, the difference in voltage between the non-inverting (+) pin and the inverting () pin is negligibly small. The input impedance between (+) and () pins is much larger than other resistances in the circuit.The input signalVinappears at both (+) and () pins, resulting in a currentithroughRgequal toVin/Rg.

Since Kirchhoff's current law states that the same current must leave a node as enter it, and since the impedance into the () pin is near infinity, we can assume practically all of the same currentiflows throughRf, creating an output voltage

By combining terms, we determine the closed-loop gainACL:

2.4 Compensation

Compensation is a process of applying a judicious patch in the form of an RC network to make up for a less than perfect op amp or circuit. There are many different problems that can introduce instability, thus there are many different compensation schemes. Internal CompensationInternal compensation provides a worst-case trade-off between stability and performance. Op amps are internally compensated to save external components and to enable their use by less knowledgeable people. External Compensation,Nobody compensates an op amp just because it is there; they have a reason to compensate the op amp, and that reason is usually stability. They want the op amp to perform a function in a circuit where it is potentially unstable. Internally and non-internally compensated op amps are compensated externally because certain circuit configurations do cause oscillations.AD829 uses external compensation.

2.5 AD829

Fig.2.2 Pin diagram of AD829 Opamp

The AD829 is a low noise , high speed op amp with custom compensation that provides the user with gains of 1 to 20 while maintaining a bandwidth >50 MHz. Its 0.04 differential phase and 0.02% differential gain performance at 3.58 MHz and 4.43 MHz, driving reverse-terminated 50 or 75 cables, makes it ideally suited for professional video applications. The AD829 achieves its 230 V/s uncompensated slew rate and 750 MHz gain bandwidth while requiring only 5 mA of current from power supplies. The external compensation pin of the AD829 gives it exceptional versatility.

Externally compensating the AD829The AD829 is stable with no external compensation for noise gains greater than 20. For lower gain, shunt feedback compensation can be used to achieve closed-loop stability. Figure 2.2 and Figure 2.3 show that shunt compensation has an external compensation capacitor, CCOMP, connected between the compensation pin and ground. This external capacitor is tied in parallel with approximately 3 pF of internal capacitance at the compensation node. In addition, a small capacitance, CLEAD, in parallel with resistor R2, compensates for the capacitance at the inverting input of the amplifier.

Fig.2.3 Inverting amplifier connection using External shunt compensation

Fig.2.4 Non-inverting amplifier connection using External shunt compensation

2.6 Experimental Setup

AIM: To design a preamplifier having variable gain using AD829 and a minimum bandwidth of 10 MHz. It was also required to filter out noise from the received signal.

Fig 2.5 Design of amplifier in Multisim

Components used:AD829Capacitors: Ccomp : 15 pF CLead : 0.001pF Two capacitors of 0.1 uF One Capacitor of 0.005uFResistors : One resistor of 50 ohm One resistor of 500 kohmPotentiometer One potentiometer of 2 Mohm

Input Data Points :-3.7404e-006 0.00322757-3.74e-006 0.00645514-3.7396e-006 0.0233378-3.7392e-006 0.0093103-3.7388e-006 0.00285516-3.7384e-006 0.0131586-3.738e-006 0.00782066-3.7376e-006 0.00744824-3.7372e-006 0.0193654-3.7368e-006 0.00384826-3.7364e-006 0.0083172-3.736e-006 0.0170068-3.7356e-006 0.0093103-3.7352e-006 0.00434481-3.7348e-006 0.0237102-3.7344e-006 0.0122896-3.734e-006 0.00571032-3.7336e-006 0.0155172-3.7332e-006 0.00695169-3.7328e-006 0.00918617-3.7324e-006 0.0186206-3.732e-006 0.00558618-3.7316e-006 0.00955858-3.7312e-006 0.0184965-3.7308e-006 0.00881375-3.7304e-006 0.00558618-3.73e-006 0.0212275-3.7296e-006 0.0115448-3.7292e-006 0.00707583-3.7288e-006 0.0120413-3.7284e-006 0.00546204-3.728e-006 0.00819307-3.7276e-006 0.019862-3.7272e-006 0.00571032-3.7268e-006 0.00670342-3.7264e-006 0.0173792-3.726e-006 0.00794479-3.7256e-006 0.00186206-3.7252e-006 0.019862-3.7248e-006 0.00943444-3.7244e-006 0.00782066-3.724e-006 0.0178758-3.7236e-006 0.0114206-3.7232e-006 0.00844134-3.7228e-006 0.0240827-3.7224e-006 0.00608273-3.722e-006 0.00968272-3.7216e-006 0.0223447-3.7212e-006 0.00943444-3.7208e-006 0.00819307-3.7204e-006 0.0191172-3.72e-006 0.0132827-2.396e-006 0.00571032-2.3956e-006 0.0125379-2.3952e-006 0.00806893-2.3948e-006 0.00173792-2.3944e-006 0.00633101-2.394e-006 0.000993099-2.3936e-006 0.00372412-2.3932e-006 0.0150206-2.3928e-006 -0.00682756-2.3924e-006 -0.00422067-2.392e-006 0.012662-2.3916e-006 0.000744824-2.3912e-006 -0.00310343-2.3908e-006 0.0124137-2.3904e-006 0.00645514-2.39e-006 0.00359998-2.3896e-006 0.0112965-2.3892e-006 0.00546204-2.3888e-006 0.00211034-2.3884e-006 0.0130344-2.388e-006 0.0029793-2.3876e-006 0.00546204-2.3872e-006 0.0100551-2.3868e-006 0.00148965-2.3864e-006 0.000372412-2.386e-006 0.0160137-2.3856e-006 0.00571032-2.3852e-006 0.00508963-2.3848e-006 0.00707583-2.3844e-006 0.00161379-2.384e-006 0.00657928-2.3836e-006 0.015393-2.3832e-006 -0.000248275-2.3828e-006 0.00260689-2.3824e-006 0.0121655-2.382e-006 0.00136551-2.3816e-006 0.000868962-2.3812e-006 0.0157654-2.3808e-006 0.00657928-2.3804e-006 -0.00049655-2.38e-006 0.0116689-2.3796e-006 0.000620687-2.3792e-006 0.00459308-2.3788e-006 0.0212275-2.3784e-006 -0.00273102-2.378e-006 0.00372412-2.3776e-006 0.0146482-2.3772e-006 0.000248275-2.3768e-006 0.000248275-2.3764e-006 0.0119172-2.376e-006 0.00546204-2.3756e-006 0.00571032-2.3752e-006 0.00868962-2.3748e-006 -0.00248275-2.3744e-006 0.0049655-2.374e-006 0.0166344

Tools used:NI Multisim 13.0

Observation:The pre-amplifier removes the ringing effect in received signal which was observed due to noise along with providing amplification.

Fig 2.6 Input and Output Waveforms

Chapter 3Development of gui using labview

3.1 Introduction

LabVIEW is short for Laboratory Virtual Instrument Engineering Workshop. It is a powerful and flexible instrumentation and analysis software development application created by the folks at National Instruments a company that creates hardware and software products, which help engineers and scientists to take measurements, control processes and store data. LabVIEW is an open development platform to develop sophisticated measurement, test, and control systems using intuitive graphical icons and wires that resemble a flowchart. Lab VIEW offers unrivaled integration with thousands of hardware devices and provides hundreds of built-in libraries for advanced analysis and data visualization. Lab VIEW ties the creation of user interfaces (called front panels) into the development cycle. Lab VIEW programs/subroutines are called virtual instruments (VIs). Each VI has three components: a block diagram, a front panel, and a connector panel. The last is used to represent the VI in the block diagrams of other, calling VIs. Controls and indicators on the front panel allow an operator to input data into or extract data from a running virtual instrument. LabVIEW provides an extensive library of virtual instruments and functions to help us in our programming.3.2 Importance & Capabilities of LabVIEWThe four critical elements of the LabVIEW development platform, which makes it superior to other platforms, are listed below: Intuitive graphical programming language High-level application-specific tools Integrated measurement and control-specific capabilities. Fig.3.1- LabVIEW Block Diagram Example

3.3 Intuitive Graphical Programming Language3.3.1 Dataflow LabVIEW is a development environment based on a graphical programming language. This approach to developing applications significantly reduces the learning curve because graphical representations are a more natural design notation for engineers and scientists than text-based code. One can access the tools and functions through interactive palettes, dialogs, and menus hundreds of function blocks, known as VIs.Data is passed from one VI to the next, eventually defining the execution order and functionality of the entire application. 3.3.2 ModularityLabVIEW naturally encourages modularity and reuse of code. Users create VIs, or code modules, with a graphical front panel that displays the inputs and outputs of the functional code as graphical controls and indicators. . Users can easily plug these VIs into other VIs, allowing for modular, hierarchical code that enables users to gradually build up complex systems.

3.3.3 Interactive execution & Debugging

The LabVIEW language is interactive as well, which means users can easily experiment with different functions in the libraries during development, which is particularly important when programming I/O resources. For example, when configuring a data acquisition (DAQ) operation, users can simply select an acquisition function from the built-in DAQ library and run it independently. This operation will actually retrieve data from the DAQ board in the computer, so the user can inspect the data to see if the operation is appropriate for the program. Debugging in LabVIEW is also interactive, featuring all of the common capabilities of traditional programming tools, such as breakpoints, step over/into/out of, and so on. A unique debugging capability of LabVIEW is the ability to visualize data anywhere within the algorithms you develop without degrading the performance of the algorithm or requiring complex programming. For example, if you are developing a complex signal-processing algorithm in LabVIEW, you can easily drop graph controls on the front panel and wire them to the data path to view the data at that point in the algorithm.

Fig 3.2- LabVIEW Computing Targets

With this wide array of computing targets, LabVIEW users can choose the right run-time environment for their application, as well as scale up or down as their requirement.

3.4 Working With RS2323.4.1 Hyper TerminalHyper terminal is an application which you can use in order to connect your computer to other remote systems.These system includes other computer, bulletin board.It is a communication and terminal emulation programme that comes with window operating system beginning with window 98.Terminal is any device that terminate one end (sender or receiver) of a communicating signal.

3.4.2Through Network Connection Turn both computers off. Connect one end of the cable into the one computer's network card, making certain that pins and holes match. Connect the other end of the cable into the other computer network card port. Turn both computers on. Decide which computer will play host when using Windows XP. Normally the computer with the needed information is the host. Go to Control Panel on the host computer; click on Network Connections. Look in Network Tasks to find "Create new connection." Click "Next." Click "Set up advanced connection" and "Next." Click "Connect directly to another computer" and "Next." Click on "Host." Choose the "serial port" as the connection device to use for the connection. Click "Next." Decide who will have access and check the corresponding boxes. Click "Next," and then "Finish." Move to computer number two, which will be your Guest Computer. The Guest Computer needs information from the Host computer. Type a name for the connection and click "Next." Repeat Step 5 on the guest computer. The setup process is complete.

SpeedSerial ports use two-level (binary) signaling, so the data rate in bits per second is equal to the symbol rate inbauds. A standard series of rates is based on multiples of the rates for electromechanicalteleprinters; some serial ports allow many arbitrary rates to be selected. The port speed and device speed must match. The capability to set a bit rate does not imply that a working connection will result. Not all bit rates are possible with all serial ports. Some special-purpose protocols such asMIDIfor musical instrument control, use serial data rates other than the teleprinter series. Some serial port systems can automatically detect the bit rate.The speed includes bits for framing (stop bits, parity, etc.) and so the effective data rate is lower than the bit transmission rate. For example with8-N-1character framing only 80% of the bits are available for data (for every eight bits of data, two more framing bits are sent).Common bit rates include 1200, 2400, 4800, 9600, 14400, 19200, 38400, 57600 and 115200 bit/s.

Data bitsThe number of data bits in each character can be 5 (forBaudot code), 6 (rarely used), 7 (for trueASCII), 8 (for any kind of data, as this matches the size of abyte), or 9 (rarely used). 8 data bits are almost universally used in newer applications. 5 or 7 bits generally only make sense with older equipment such as teleprinters.

ParityParityis a method of detecting errors in transmission. When parity is used with a serial port, an extra data bit is sent with each data character, arranged so that the number of 1 bits in each character, including the parity bit, is always odd or always even. If a byte is received with the wrong number of 1s, then it must have been corrupted. However, an even number of errors can pass the parity check.The parity bit in each character can be set to none (N), odd (O), even (E), mark (M), or space (S). None means that no parity bit is sent at all. Mark parity means that the parity bit is always set to the mark signal condition (logical 1) and likewise space parity always sends the parity bit in the space signal condition. Aside from uncommon applications that use the 9th (parity) bit for some form of addressing or special signaling, mark or space parity is uncommon, as it adds no error detection information. Odd parity is more common than even, since it ensures that at least one state transition occurs in each character, which makes it more reliable. The most common parity setting, however, is "none", with error detection handled by a communication protocol.

Stop bitsStop bits sent at the end of every character allow the receiving signal hardware to detect the end of a character and to resynchronize with the character stream. Electronic devices usually use one stop bit. If slow electromechanicalteleprintersare used, one-and-one half or two stop bits are required.The D/P/S (Data/Parity/Stop) conventional notation specifies the framing of a serial connection. The most common usage on microcomputers is 8/N/1 (8N1). This specifies 8 data bits, no parity, 1 stop bit. In this notation, the parity bit is not included in the data bits. 7/E/1 (7E1) means that an even parity bit is added to the seven data bits for a total of eight bits between the start and stop bits. If a receiver of a 7/E/1 stream is expecting an 8/N/1 stream, half the possible bytes will be interpreted as having the high bit set.

Flow controlA serial port may use signals in the interface to pause and resume the transmission of data. For example, a slow printer might need to handshakewith the serial port to indicate that data should be paused while the mechanism advances a line. Common hardware handshake signals use the RS-232 RTS/CTS, DTR/DSR signal circuits. Generally, the RTS and CTS are turned off and on from alternate ends to control data flow, for instance when a buffer is almost full. DTR and DSR are usually on all the time and are used to signal from each end that the other equipment is actually present and powered-up.

3.5 Interfacing Through LabVIEW1. Open LabVIEW.2. Open a blank VI.3. Open the block diagram of VI. Select window>> show block diag(bd diagram)4. Place the VISA Configure Serial Port to initializes the serial port specified by VISA resource name to the specified settings. The VISA class wired to the VISA resource name input determines the polymorphic instance to use.

5. Open LabVIEW.6. Open a blank VI.7. Open the block diagram of VI. Select window>> show block diag (bd diagram)8. Place the VISA Configure Serial Port to initializes the serial port specified by VISA resource name to the specified settings. The VISA class wired to the VISA resource name input determines the polymorphic instance to use.

If function palette is not already open select view >> control palette from the LabVIEW menu. Select Instrument I/O>>VISA>>VISA Advanced>>Bus/Interface Specific>>Serial>>Configure port. Place the configure port on the block diagram.

FIG.3.3-GUI for Nd:YAG laserREFERENCES

1. MULTISIM HELP2. LABVIEW BASICS , II COURSE MANUAL3. LABVIEW HELP4. ROBERT H.BISHOP LEARNING WITH LABVIEW 7 EXPRESS.5. Dr. Jai pal Dudeja, Dr. S Veerabuthiran, LASTEC, Metcalfe House, Delhi-54, LIDAR TECHNOLOGY AND APPLICATIONS , October 20066. AD829 DATA SHEET7. ULTRA USER MANUAL