AUDIO VIDEO SYSTEMS

Transcription

1 AUDIO VIDEO SYSTEMS PROF. PRATIKGIRI GOSWAMI ASSISTANT PROFESSOR ELECTRONICS & COMMUNICATION DEPARTMENT, L. D. COLLEGE OF ENGINEERING

2 QUANTIZATION & ENCODING

3 QUANTIZATION & ENCODING Assume that sampling its amplitude at 32 levels Period of wave shape is one second sampling at 100 ms intervals 10 samples available during each cycle. Five bit code 32 levels bit sequence as shown in figure for example, 19 is represented with bit A/D converter Clock pulses sampling rate Nyquist criterion 625/50 TV Bandwidth 5 MHz sampling rate must be 10 MHz or faster PAL System sampling rate = 3 x f sc bit rate of 200 Mbits/sec

4 QUANTIZATION & ENCODING 256 level sampling 8 bit code Black level 64 th level with code Peak White level 204 with code

5 QUANTIZATION & ENCODING Audio Quantization: sampling level can range from 64 to 128 depending on the desired sound output quality. CDs 128 sampling levels 7 bits Encoder :

6 DIGITAL SATELLITE TV Because of merits of processing signals in digital form, digital satellite transmission and reception is now common. However, signal distribution to subscribers is mostly through cable networks in analog form. Four Stages : 1. Signal Encoding 2. Processing 3. Modulation 4. Transmission

7 UP-LINK

8 SIGNAL PROCESSING Three Stages : 1. Compression 2. Encryption 3. Packetising Compression : data rate required to transmit digital information is around 200 Mbps and needs channel bandwidth of 50 MHz with provisions for very expensive processing equipments. compression techniques reduce data rate to about 3 to 6 Mbps compression algorithms done in previous chapter motion prediction MPEG etc. Audio Compression eliminating soft sounds that are near louds because their absence at Rx would not matter much on account of limitations of human ear compressed audio data rate can vary from 50 kbps for mono to near 300 kbps for stereo sounds.

9 SIGNAL PROCESSING Encryption : to prevent unauthorized reception of channels for which a special fee is to be paid encrypted before up-linking, by inserting keys keys for decryption are also transmitted with channel data to enable authorized customers to restore normal reproduction of signals. done by inserting a card called SMART CARD in decoder

10 SIGNAL PROCESSING Data Packets : besides audio and video signals, conditional information is also transmitted to the customer which includes access data, PC compatible data and program guide. combined in form of packet which also contains signals to register identity of each packet thus enabling their separation at receiving end. all the packets are time multiplexed into serial data before further processing at transmitting site.

11 RECEPTION AND DECODING

12 DIRECT-TO-HOME SATELLITE TV enables viewers to receive many channels of high quality TV programs via high powered Ku-Band satellites. no distribution cables but the Rx connects through MODEM to the customers telephone line for communication with the subscription service computer for billing purpose. differs in terms of compression from digital satellite TV economics point of view data should be compressed till significant artifacts appear. movies vs basket ball game Ku-band freq are preferred as these are not prone to interference from ground point-to-point communication and also need much smaller diameter dish antenna.

13 DIRECT-TO-HOME SATELLITE TV ku-band 11.7 to GHz high powered 12.2 to 12.7 GHz for efficient operation of DTH Transmission requires dish antennas of diameter between 50 to 90 cm depending on the location of receiving site DTH Rx Front Panel

14 DIRECT-TO-HOME SATELLITE TV TV/DTH or TV/DSB : switches between the satellite signal IN and the terrestrial antenna or cable network IN as desired on turning ON the receiving.

15 DIRECT-TO-HOME SATELLITE TV Out to with modulation on Channel 3 or 4 S video which connects Super Video to the compatible TV set or VCR Wide Band for use in conjunction with future technology such as HDTV and Interactive TV.

16 DIGITAL TV Rx

17 DIGITAL TV Rx RF signal from antenna is demodulated and amplified in tuner in the conventional way to obtain IF output. Demodulated signal is digitized and presented to DSP circuits with the aid of micro-computer. clock freq for the digital circuits is derived from the color subcarrrier burst video signal digitized with 256 levels audio digitized at around 32 KHz in 14 bit resolution

18 DIGITAL TV Rx CCU Central Control Unit Heart micro computer based device which controls and coordinates all the circuits and signal processing functions and provides a user interface. Enables a total flexibility to the user who can control receiver functions, display teletext, obtain multiple picture-in-picture displays for simultaneous viewing of different programs and zooming of the picture. Video Codec : converts analog composite video signal by high speed flash A/D converter into 8 bit digital signal

19 DIGITAL TV Rx Video Processor : separates into two channels luminance and chrominance luminance multiplier brightness, contrast in accordance with the user s choice chrominance encodes relative weightage of R, G and B in electron guns consists of a bandpass filter, an automatic color circuit, a comb filter and color decoder. two streams of signals are then sent back to the video codec which also contains D/A converters to obtain outputs in analog form. Then delay line technique is employed for averaging and later demodulation to obtain U and V outputs which are suitably combined to obtain R-Y, B-Y and G-Y

20 DIGITAL TV Rx Deflection Processing Unit : senses the standard TV signal and synchronizes the vertical and horizontal sweep generators by counting the color subcarrier and locking to it. Audio Codec : samples input signal to produce 1 bit data stream and then converts into 16 bit resolution stream at 35 KHz. The digital identification filter takes out the identification signal and tells whether the broadcast is mono, stereo or bilingual.

21 MERITS OF DIGITAL TV Rx Reduced Ghosts : due to better synchronization Reduction of 50 Hz Flicker : faster rescanning of each picture High Resolution Pictures : picture storage capacity is higher in digital possible to scan second set of lines in-between then usual scan lines thus enabling high resolution picture with the same low resolution incoming signal. Picture-in-Picture (PIP) : to see two programs at the same time Slow Motion Action : each frame can be scanned onto screen several times to freeze the frame Easy adoption to additional displays

22 MERITS OF DIGITAL TV Rx Reduced Operational Instability : effect of component aging on alignment etc and consequent instability encountered in analog receivers is eliminated self tuning and easy routine adjustments

23 DIGITAL TERRESTRIAL TV digital technology and fabrication of VLSI chips digital TV transmission by terrestrial means two decades back despite the fact that digital transmission needs more BW which is too large for a ground based broadcast system. transition from analog to digital terrestrial is slow because of replacement cost of existing equipments at the studios and transmitters. at the receiving end millions of analog Rx in use would need to be discarded or at least provided with converter Another reason for DTT not receiving much attention Satellite TV changing from analog to digital high gain dish antenna to receive broadcasts distribution to subscribers via cables degradation of quality solution DTH major limitation on number of channels available to subscriber

24 STEREO SOUND SYSTEMS Besides loudness, to enable perception of both direction and depth of sound necessary to have two completely separate channels at the Tx and independent detection and amplifying paths in the Rx. Stereo Sound Principle : obtained by placing two mic in front of the stage as shown in figure

25 STEREO SOUND SYSTEMS different lengths of sound path lines time delay in both microphones sound pattern picked up by each mic is fed to its own recording and reproduction channel listener sitting in the centre between two loudspeakers then listens the difference between two sound patterns. FM-FM Stereo

26 STEREO SOUND SYSTEMS FM-FM stereo multiplex where only one FM Tx is used to broadcast both the channel audio signals. pilot signal carrier to synchronize detection in the Rx. at Rx separate L+R and L-R components in their original form (L+R)+(L-R) = 2L and (L+R) (L-R) = 2R Stereo sound in Television accommodated in a different way as devised by PHILIPS IF spectrum consists of vision carrier, first sound carrier at 5.5 MHz and a second sound IF at MHz from vision carrier. both sound carriers are separated by 15.5 x f H to minimize interference.

27 STEREO SOUND SYSTEMS The first sound IF is freq modulated with (L+R) so that mono TV Rx can still reproduce mono sound second IF is FM modulated with 2R information To identify whether transmitted signal is mono or stereo, second IF carrier also carries an identification signal which is KHz pilot carrier amplitude modulated with Hz for stereo or Hz for dual transmission. Stereo information 2(L+R)-2R=2L

28 STEREO SOUND SYSTEMS

29 PROJECTION SYSTEMS CRT Projection on large screen brightness and clarity problems to overcome, new technology called Micro Electro-Mechanical (MEMS) was developed in which, chips like Digital Micromirror Devices (DMD) are used to develop the picture FRONT and REAR display type are now used in Home Entertainemnt Theatres with installation of Dolby Sound System. Direct View Projection System : conventional TV picture tube uses three electron beams and separate phosphors for for R, G, B one looks directly at the surface that TV uses to create the composite picture Rear Projection System : three different CRTs on splitting the video signal produce R, G, B their combined effect can produce the entire visual spectrum for this, CRTs project onto a mirror which bounces the full color image on a fairly large screen located in the upper half of TV box.

30 PROJECTION SYSTEMS Front Projection System : projection and screen are two separate units where the projector projects images onto the front of screen just like theatres Both REAR and FRONT projection configurations use tiny devices like small CRT tube or LCD panels for creating pictures. These devices are called REFLECTIVE meaning that the source incident light picks up to picture by reflecting i.e. bouncing off the device. Some other devices TRANSMITTIVE meaning that the incident light picks up picture by travelling through device which is then magnified by lenses before projections onto the screen.

31 TRANSMITTIVE TYPE CRT Transmittive Projectors : smaller around 9 CRTs are used which emit very bright light lens is put in front of CRT which magnifies image and projects Three configurations One color CRT : color image formed on its screen is magnified with one lens and projected on screen One B&W CRT with color filters : fast rotating color filter wheel with R,G, B segments placed between CRT and projection lens results in rapidly changing three color images forms single colored image due to high speed of wheel and ability of our eyes to integrate them. Three CRTs : one for each primary color three lenses Aligned such that a single colored image appears on the screen

32 TRANSMITTIVE TYPE LCD Transmittive Projectors : to make projectors light and to increase the resolution uses bright light to illuminate the LCD panel image formed is projected by lens system on the screen Transmittive Projectors gradually replaced by reflective type

33 REFLECTIVE TYPE image is formed on a small reflective chip when light shines on the chip, image is reflected off it and through a projection lens gets focused on the screen. MEMS : Two main MEMS systems : DMD and GLV (Grating Light Value) These have a moveable or deformable reflective surface on top of semiconductor chip. Chip generates voltages in response to digital information. These voltage changes the reflective surface rapidly in a controlled way to produce the image that was encoded by the digital information. Projected light bounces off the reflective surface and gets collected by the projector lens.

34 DMD also called digital light processing (DLP), developed by Texas Instruments, USA is small chip that has anywhere up to multi-million tiny mirrors on it depending on the size of the array. Each mirror consists of three physical layers and two air gap layers. The air gap layers separate three physical layers and allow the mirror to tilt +10 or -10 degree. When a voltage is applied to either of the address electrodes, the mirrors tilt representing ON or OFF in a digital signal. Projector light shines on DMD. Light hitting ON mirror will reflect through the projection lens to the screen. ON mirrors will produce bright area on the screen and OFF mirrors dark area. Each mirror is individually controlled. Combination of all mirrors produces monochrome picture on screen. To add colors, 3 color wheel is used.

35 GLV licensed by Sony consists of tiny reflective ribbons mounted over a silicon chip. Ribbons are suspended over a chip with small air gap in between. When voltage is applied below ribbon, ribbon moves towards the chip by a fraction of wavelength of illuminating light. the deformed ribbons form a diffraction grating and various orders of such a light can be combined to form the pixels of an image. The shape of ribbons and therefore image formation can be changed in as little as 20 billions of a second.

36 PROJECTION TELEVISION obtaining large picture from a relatively small picture tube for many applications such as lecture class and medical demonstrations. It is not possible to produce a picture tube with screen area exceeding 40 diagonal due tohigh cost and technological difficulties. simplest projection TV is one in which picture obtained on the screen of a picture tube is enlarged by lens system and projection on a large screen. brightness is low and necessary to darken the room improved version produces much brighter R, G and B with special tubes two piece system positions are fixed for optimum image reproduction Matsushita Electric Co. of Japan produced a complete and compact projection TV system

37 PROJECTION TELEVISION light from the projector is reflected by a mirror on the screen which is assembled along in the same unit. screen size is nearly 150 cm square grown over the years

38 FLAT PANEL DISPLAY conventional picture tube is replaced by flat panel display led to development of LCD and active matrix displays LCDs : simple dot matrix approach Active Matrix Displays : Matsushita produced initially a colour displays with 10 diagonal technology known as matrix drive and deflection in fact an array of 3000 very small electron tubes with an effective resolution of 270 scanning lines display panel measures 370 x 355 x 99 mm made up of lattice electrodes approximately 0.1 mm thick layered between insulating boards.

39 FLAT PANEL DISPLAY

40 FLAT PANEL DISPLAY has 15 very fine wire cathodes and 200 electron beam control electrodes set 200 across and 150 high, deflected in six stages. with the interlaced included, total deflection stage is 32 with output of 1,92,000 pixels in a 400 x 480 matrix. LCD : screen consists of a liquid crystal solution put-in between two glass plates on application of current acts like a shutter to allow more or less light to pass through depending on the intensity of applied charge that is proportional to the applied signal PLASMA : special solution is coated on the inner side of two glass plates has millions of phosphor coated gas bubbles containing plasma application of current triggers phosphors to emit light which in turn combine to create pictures on screen

41 PLASMA PANELS For years, the most common display technology has been the cathode ray tube or CRT. In the last few years, around 115 million new CRT computer monitors and 130 million new television sets based on CRT technology have been sold annually throughout the world. CRTs have been produced in large volumes for over 50 years and consequently, manufacturers have developed very efficient processes and enjoy great economies of scale. This means that CRT technology delivers a good performance at relatively low cost.

42 PLASMA PANELS But now there are newer, slimmer, lighter and more versatile products that are true alternatives to the traditional CRT device. Currently, the most popular technologies are: Plasma display panel, PDP. Liquid crystal display, LCD. Digital light processing, DLP. There are other technologies that are being developed such as organic light-emitting diodes (OLED), field emissive displays and surface conduction electron-emitter displays (SED). The CRT is a well tried and tested technology and remains the standard for standard definition picture quality. Nonetheless, flat panel displays (FPDs) have a number of advantages that makes them more desirable than the CRT.

43 PLASMA PANELS These advantages are: Fully flat display. Large screen formats. Thin (40 mm) suitable for wall hanging. Small in size occupying less desk space. Fully digital internal operation. Light weight 1/6th of CRT. Unaffected by magnetic fields. Fully flicker-free operation. Larger viewing area a 15 flat panel gives the same viewable screen as a 17 CRT. High resolution.

44 PLASMA PANELS On the other hand, flat panels have disadvantages, but these are different depending on the type of FPD under consideration. In general, however, FPDs are more complex, more expensive, have restricted viewing angle and use more power than the comparable conventional CRT display.

45 VIEWING ANGLE Traditional CRT displays may be viewed at virtually any angle without degradation in color or brightness. The same cannot be said of flat panel displays FPDs. FPDs are specified with a viewing angle defined as the angle (horizontal and vertical) from which the display can be correctly seen without discoloring or brightness degradation. Most FDPs have a viewing angle of 160 V and H. That means that a picture may be viewed at 80 (160 /2) from a line drawn vertically from the centre of the screen. Given that at 90 the viewer is facing the edge of panel, such a viewing angle is a very tall order. Some manufacturers claim a viewing angle as high as 170. That being said, a viewer may find that images at the extreme ends of the specified viewing angle do not provide comfortable viewing or good picture quality.

46 MATRIX FORMAT All flat panels consist of a number of picture elements, known as pixels arranged in a matrix format of rows and columns. For colour production, each pixel is sub-divided into three sub-pixels or cells.

47 RESOLUTION The resolution of an FPD is defined as the number of pixels that make up the panel. It is specified as X x Y where X and Y are the number of pixels in the horizontal and vertical directions respectively. Although a flat panel may be manufactured with any resolution, the following is the accepted standard resolutions:

48 PIXEL SPECIFICATIONS

49 PIXEL SPECIFICATIONS Typical values for a PDP are 1080 micrometer (H) and 810 micrometer (V) for a 42 in. VGA panel. For high resolution PDPs, a typical pixel pitch could be as low as 800 micrometer (H) and 500 micrometer (V). The size of a cell is normally defined by its horizontal pitch or width which is the distance between the middle point of adjacent cells. A cell also has a vertical pitch dimension which is the same as the pixel pitch (vertical). The cell pitch depends on screen size as well as resolution. A typical cell width for a PDP is between 360 and 300 micrometer. The final specification of a pixel is the rib width and height (or vertical) dimensions, typically 80 and 150 micrometer respectively for a plasma panel. For deep cell construction, the rib height is doubled.

50 3D TV Two dimensional lack of depth 3D TV : picture appears to have all the qualities of a live scene as viewed with natural vision. picture seems to extend beyond the screen at its back and also in front. our eyes see a slightly different image of the same scene while viewing and brain interprets these as a single composite image in 3D. cameras are located suitably like the eyes in practice, many such pairs accompanied with stereo sound L and R channels are independently freq modulated with 5.5 MHz sound carrier

51 3D TV Left and Right channel signals thus formed together with sync pulses are amplitude modulated with the station channel carrier in separate modulators.

52 EDTV referred to improved performance of TV systems that require different transmission standards but retain the present line number and field rates. mainly intended for new delivery media such as direct broadcasting satellite (DBS) conventional system creates problems of interference beats called cross luminance and cross colour effects associated with areas of high colour saturation new encoding system called Multiplexed Analog Components (MAC) was proposed lumi and chromi signals are time multiplexed sent in time sequence in different components in the time of a normal horizontal line

53 EDTV Compression of Signal : lumi and chromi signals are individually time compressed so as to accommodate them in 64 usec line scanning period lumi compressed by factor 3:2 and this reduces the time occupied by it from 52.5 usec to 35 usec color diff signal by factor 3:1 reducing time to 17. usec compressed lumi signal is transmissted on each line with compressed chromi components (R - Y) OR (B - Y), the complementary is trnamissted in next line. compression rates are slightly adjusted to leave about 10 usec for digital sync and sound/data signals.

54 EDTV

55 HDTV It aims at : (1) improvement in both vertical and horizontal resolution of reproduced picture by approx 2:1 over existing standards. (2) much improved colour reproduction (3) higher aspect ratio of at least 5:3 (4) stereophonic sound NHK, the Japan Broadcasting Corporation Tokyo worldwide pioneer in HDTV adopted 1125 scanning lines per frame, 60 fields per second, 2:1 interlace scan, aspect ratio 16:9 Europe its own standard EUREKA compatible with CCIR but with 1249 lines and aspect ratio 16:9 NHK Rx expensive and complex, too much RF BW required (approx 10 MHz compared to 6 MHz in NTSC) final decision on adapting a compatible system has now been taken with enough progress to fully developing it.

56 HDTV NHK MUSE System : MUSE stands for Multiple Sub-Nyquist Sampling Encoding It is an HDTV bandwidth compression scheme developed by NHK uses fundamental concepts of performance exchange of the spatiotemporal (transitory transformation) domain along with motion compression to reduce the transmission BW down to near 10 MHz. Lumi and Chromi signals are transmitted using Time Multiplexed Components (TMC). Colour information is sent sequentially with a time compression of four. TMC signal is BW reduced by means of 3-dimensional offset subsampling pattern over a four-field sequence. The stationery areas of the picture are reconstructed by temporal interpolation of samples from four fields.

57 HDTV Moving picture area final picture is reconstructed by spatial interpolation using samples from a single field moving portions of the picture are reproduced with one-quarter the spatial resolution of the stationary areas. Spatial freq response for both stationary and moving areas of the picture is shown in figure.

58 HDTV A vector representing the motion of the scene is calculated for each field at the encoder. This signal is multiplexed in the vertical blanking interval and transmitted to the receiver. In the decoder, the read-out address of pixels from previous fields are shifted according to the information provided by the motion vector so that the data can be processed in the still-picture mode. These two modes of interpolation, inter-frame processing for stationary pictures and intra-field averaging for moving portions of the picture, are switched by detecting the moving areas at the decoder. Audio transmission is done by DPSK (Digital PSK), which is multiplexed with the processed video signal in the vertical blanking interval after frequency modulation of the transmission carrier by the video signal.

59 THANK YOU PROF. PRATIKGIRI GOSWAMI