Analog televizor - Analog television

Ushbu maqolada bir nechta muammolar mavjud. Iltimos yordam bering uni yaxshilang yoki ushbu masalalarni muhokama qiling munozara sahifasi. (Ushbu shablon xabarlarini qanday va qachon olib tashlashni bilib oling) Bu maqola uchun qo'shimcha iqtiboslar kerak tekshirish. Iltimos yordam bering ushbu maqolani yaxshilang tomonidan ishonchli manbalarga iqtiboslarni qo'shish. Ma'lumot manbasi bo'lmagan materialga qarshi chiqish va olib tashlash mumkin. Manbalarni toping: "Analog televizor"  – Yangiliklar  · gazetalar  · kitoblar  · olim  · JSTOR (2014 yil sentyabr) (Ushbu shablon xabarini qanday va qachon olib tashlashni bilib oling) Bu maqola aksariyat o'quvchilar tushunishi uchun juda texnik bo'lishi mumkin. Iltimos uni yaxshilashga yordam bering ga buni mutaxassis bo'lmaganlarga tushunarli qilish, texnik ma'lumotlarni olib tashlamasdan. (2014 yil sentyabr) (Ushbu shablon xabarini qanday va qachon olib tashlashni bilib oling) (Ushbu shablon xabarini qanday va qachon olib tashlashni bilib oling)

Ovozni boshqarish va kanalni tanlash uchun katta raqamli terishlarga ega bo'lgan erta monoxromli analog qabul qilgich, aniqroq sozlash, yorqinlik, kontrast va gorizontal va vertikal ushlab turish uchun kichikroq

Analog televizor asl nusxasi televizor foydalanadigan texnologiya analog signallar video va audio uzatish uchun.^[1] Analog televizion eshittirishda yorqinlik, ranglar va tovush quyidagicha ifodalanadi amplituda, faza va chastota analog signal.

Analog signallar mumkin bo'lgan qiymatlarning uzluksiz diapazonida o'zgarib turadi, bu degani elektron shovqin va shovqin kiritilishi mumkin. Shunday qilib analog bilan o'rtacha zaif signal bo'ladi qorli va aralashuvga bog'liq. Aksincha, rasm sifati a raqamli televidenie (DTV) signal qabul qilishning iloji bo'lmagan yoki vaqti-vaqti bilan bo'ladigan darajadan pastroq darajaga tushguncha yaxshi qoladi.

Analog televizor simsiz bo'lishi mumkin (er usti televidenie va sun'iy yo'ldosh televideniesi ) yoki kabeli tarmoq orqali tarqatilishi mumkin kabel televideniesi.

Hammasi efirga uzatiladigan televizion tizimlar DTV kelishidan oldin analog signallardan foydalangan. Pastki tarmoqli o'tkazuvchanligi talablari asosida siqilgan raqamli signallar, 2000 yillardan beri a raqamli televizion o'tish analogli eshittirishlarni to'xtatishning turli muddatlari bilan dunyoning aksariyat mamlakatlarida davom etmoqda.

Rivojlanish

Analog televizorning dastlabki tizimlari bo'lgan mexanik televizor tasvirni skanerlash uchun diskka teshilgan teshiklari bo'lgan yigiruv disklaridan foydalangan tizimlar. Shunga o'xshash disk qabul qilgichdagi tasvirni qayta tikladi. Qabul qiluvchilarni disklarini aylanishini sinxronlashtirish tasvir ma'lumotlari bilan efirga uzatiladigan sinxron impulslar orqali amalga oshirildi. Kamera tizimlarida shu kabi yigiruv disklari ishlatilgan va yorug'lik detektori ishlashi uchun predmetning kuchli yoritilishini talab qilgan. Ushbu mexanik tizimlardan olingan tasvirlar xira, juda past piksellar soniga ega edi va qattiq miltilladi.

Analog televideniye rivojlanmaguncha sanoat sifatida boshlangan emas katod-nurli naycha (CRT), a bo'ylab chiziqlarni kuzatishda yo'naltirilgan elektron nurlarini ishlatadi fosfor qoplamali sirt. Elektron nur har qanday mexanik disk tizimiga qaraganda ekran bo'ylab ancha tezroq siljishi mumkin edi, bu esa skanerlash chiziqlari va tasvir o'lchamlarini ancha yuqori bo'lishiga imkon berdi. Bundan tashqari, mexanik yigiruv disklari tizimiga nisbatan barcha elektron tizimlarga nisbatan kamroq texnik xizmat ko'rsatish talab qilingan. Keyinchalik barcha elektron tizimlar uy xo'jaliklari orasida mashhur bo'ldi Ikkinchi jahon urushi.

Standartlar

Analog televizion eshittirishlar turli xil tizimlardan foydalangan holda o'zlarining signallarini kodlashadi. Rasmiy uzatish tizimlari quyidagicha nomlangan: A, B, C, D, E, F, G, H, I, K, K1, L, M va N.^{[iqtibos kerak ]} Ushbu tizimlar skanerlash satrlari sonini, kvadrat tezligini, kanal kengligini, video o'tkazuvchanligini, video-audio ajratilishini va boshqalarni aniqlaydi.

Ushbu tizimlardagi ranglar uchta rang kodlash sxemasidan biri bilan kodlangan: NTSC, PAL, yoki SECAM,^[2] va keyin foydalaning RF modulyatsiyasi ushbu signalni a ga modulyatsiya qilish juda yuqori chastota (VHF) yoki ultra yuqori chastotali (UHF) tashuvchi to'lqin. Televizion tasvirning har bir kadri tarkib topgan skanerlash chiziqlari ekranda chizilgan. Chiziqlar har xil yorqinlikda; butun chiziqlar to'plami tezda chizilganki, inson ko'zi uni bitta tasvir sifatida qabul qiladi. Jarayon takrorlanadi va keyingi ketma-ket kadr ko'rsatiladi, bu harakatni tasvirlashga imkon beradi. Analog televizion signal qabul qiluvchining ikki o'lchovli harakatlanuvchi tasvirni bir o'lchovli vaqt o'zgaruvchan signalidan tiklashi uchun vaqt va sinxronizatsiya ma'lumotlarini o'z ichiga oladi.

Birinchi tijorat televideniesi tizimlar edi qora va oq; ning boshlanishi rangli televizor 1950-yillarda edi.^[3]

Amaliy televizion tizimni qabul qilish kerak nashrida, xrominans (rang tizimida), sinxronizatsiya (gorizontal va vertikal) va audio signallari va ularni radio uzatish orqali tarqatish. Transmissiya tizimida vositasi bo'lishi kerak televizion kanal tanlov.

Analog efirga uzatiladigan televizion tizimlar turli xil kvadrat stavkalari va o'lchamlari mavjud. Boshqa farqlar audio tashuvchining chastotasi va modulyatsiyasida mavjud. 1950 yillarda mavjud bo'lgan monoxrom kombinatsiyalar Xalqaro elektraloqa ittifoqi (ITU) A dan N gacha katta harflar bilan rangli televizor paydo bo'lganda, rang va to'yinganlik to'g'risidagi ma'lumotlar bir rangli signallarga qora va oq televizorlar e'tiborsiz qoldiradigan tarzda qo'shilgan. Shu tarzda orqaga qarab muvofiqlikka erishildi. Ushbu kontseptsiya barcha analog televizion standartlar uchun amal qiladi.

Qo'shimcha rangli ma'lumotlarni kodlash va uzatishning uchta standarti mavjud edi. Birinchisi, Amerikaning NTSC (Milliy Televizion Tizimlar Qo'mitasi) rangli televizion tizim edi. Keyinchalik Evropa / Avstraliyaning PAL (Faza Alternation Line stavkasi) va Frantsiya-sobiq Sovet Ittifoqi SECAM (Séquentiel Couleur Avec Mémoire) standarti keyinchalik ishlab chiqilgan va NTSC tizimining ayrim nuqsonlarini davolashga harakat qilingan. PAL-ning rang kodlashi NTSC tizimlariga o'xshaydi. SECAM, PAL yoki NTSC dan farqli o'laroq, boshqa modulyatsiya usulini qo'llaydi.

Aslida, uchta rang kodlash tizimining har qanday skanerlash liniyasi / kvadrat tezligi kombinatsiyasi bilan birlashtirilishi mumkin. Shuning uchun, berilgan signalni to'liq tavsiflash uchun rang tizimidan va eshittirish standartidan bosh harf sifatida iqtibos keltirish kerak. Masalan, Amerika Qo'shma Shtatlari, Kanada, Meksika va Janubiy Koreyada NTSC-M (ularning aksariyati raqamli tizimga o'tilgan), Yaponiyada NTSC-J (Yaponiya raqamli (ISDB) ga o'tganda 2012 yilda ishlab chiqarilishi to'xtatilgan)), Buyuk Britaniya PAL-I dan foydalanadi (2012 yilda Buyuk Britaniya raqamli (DVB-T) ga o'tganda to'xtatilgan), Frantsiya SECAM-L dan foydalanadi (2011 yilda to'xtatilgan, Frantsiya raqamli (DVB-T) ga o'tganda), G'arbiy Evropa va Avstraliyaning katta qismi PAL-B / G (ularning aksariyati raqamli televidenie standartlari sifatida DVB-T ga o'tdi yoki o'tdi), Sharqiy Evropaning aksariyat qismida SECAM-D / K yoki PAL-D / K va boshqalar qo'llaniladi.

Biroq, bu mumkin bo'lgan kombinatsiyalarning barchasi ham mavjud emas. NTSC hozirda faqat M tizimi bilan ishlaydi, garchi Buyuk Britaniyada NTSC-A (405 liniyasi) va Janubiy Amerikaning bir qismida NTSC-N (625 liniyasi) bilan tajribalar bo'lgan. PAL turli xil 625 qatorli standartlarda (B, G, D, K, I, N), shuningdek Shimoliy Amerikada 525 qatorli standartlarda qo'llaniladi KAFT. Xuddi shu tarzda, SECAM turli xil 625 qatorli standartlarda qo'llaniladi.

Shu sababli ko'pchilik raqamli signallarga murojaat qilganda ham 625/25 turdagi har qanday signalni "PAL" deb, 525/30 har qanday signalni "NTSC" deb atashadi; masalan, ustida DVD-video, bu analog rang kodlashni o'z ichiga olmaydi va shuning uchun PAL yoki NTSC signallari umuman yo'q. Ushbu foydalanish odatiy bo'lsa ham, u noto'g'ri, chunki bu PAL / SECAM / NTSC atamalarining asl ma'nosi emas.

Dunyo bo'ylab bir nechta turli xil televizion tizimlar ishlatilgan bo'lsa-da, xuddi shu ishlash tamoyillari amal qiladi.^[4]

Ko'pgina mamlakatlarda havo orqali efirga uzatuvchi televizion dastur ning analog audio va analog video televizion eshittirishdan qayta foydalanishga ruxsat berish uchun signallar to'xtatildi radio spektri kabi boshqa xizmatlar uchun ma'lumotlar to'plami va subkanallar.

Rasmni ko'rsatish

A katod-nurli naycha (CRT) televizion tasvirni nurni skanerlash orqali namoyish etadi elektronlar a sifatida tanilgan gorizontal chiziqlar naqshida ekran bo'ylab raster. Har bir satr oxirida nur keyingi satr boshiga qaytadi; oxirgi satrning oxiri - ekranning yuqori qismiga qaytadigan havola. Har bir nuqtadan o'tayotganda nurning intensivligi o'zgaradi va o'zgaradi nashrida shu nuqtadan. A rangli televizor tizim bir xil, faqat qo'shimcha signal sifatida tanilgan xrominans dog'ning rangini boshqaradi.

Rastrli skanerlash quyida biroz soddalashtirilgan shaklda ko'rsatilgan.

Analog televizion ishlab chiqilganda, har qanday video signallarni saqlash uchun arzon texnologiya mavjud emas edi; yorug'lik signalini CRT-da ko'rsatadigan bir vaqtning o'zida yaratish va uzatish kerak. Shuning uchun kamerada (yoki signalni ishlab chiqaruvchi boshqa moslamada) raster skanerlashni aniq bajarish kerak sinxronizatsiya televizorda skanerlash bilan.

CRT fizikasi nuqta keyingi satr boshiga qaytishi uchun cheklangan vaqt oralig'iga ruxsat berilishini talab qiladi (gorizontal qaytish) yoki ekranning boshlanishi (vertikal retrasiya). Yorug'lik signalining vaqti bunga imkon berishi kerak.

Analog rangli ekran tasvirini yoping

Inson ko'zining o'ziga xos xususiyati bor Phi hodisasi. Birin-ketin skanerlash tasvirlarini tezda namoyish qilish ko'rinishga imkon beradi xayol silliq harakat. Rasmning miltillashini CRT ustidagi uzoq davom etadigan fosforli qoplama yordamida qisman hal qilish mumkin, shuning uchun ketma-ket tasvirlar sekin o'chib ketadi. Shu bilan birga, sekin fosfor salbiy tezkor ta'sirga ega bo'lib, ekranda katta miqdordagi tezkor harakatlar sodir bo'lganda, rasmning bulanishi va xiralashishiga olib keladi.

Maksimal kvadrat tezligi ga bog'liq tarmoqli kengligi elektronika va uzatish tizimining tasviri va rasmdagi gorizontal ko'rish satrlari soni. 25 yoki 30 kvadrat tezligi gerts jarayoni qoniqarli kelishuvdir interlacing ikkitasi video maydonlari rasmning per ramka tasvirni yaratish uchun ishlatiladi. Ushbu jarayon soniyada aniq sonli videokameralar sonini ikki baravarga oshiradi va miltillovchi va uzatishda boshqa nuqsonlarni kamaytiradi.

Displey ekranlarining boshqa turlari

Plazma ekranlari va LCD ekranlar analog sifatida ishlatilgan televizorlar. Ushbu turdagi ekranlar eski CRT displeylarga qaraganda past kuchlanishlardan foydalanadi. Ko'p ikkita tizim televizion qabul qiluvchilar, ikkalasini ham qabul qilish uchun jihozlangan analog uzatish va raqamli uzatmalar analogga ega sozlovchi qabul qilish qobiliyati va foydalanish kerak a televizion antenna.

Signallarni qabul qilish

Har bir mamlakat uchun televizion tizim UHF yoki VHF chastota diapazonidagi bir qator televizion kanallarni belgilaydi. Kanal aslida ikkita signaldan iborat: rasm ma'lumotlari yordamida uzatiladi amplituda modulyatsiya bitta chastotada va ovoz bilan uzatiladi chastota modulyatsiyasi rasm signalidan belgilangan ofsetda (odatda 4,5 dan 6 MGts gacha) chastotada.

Tanlangan kanal chastotalari etarlicha ruxsat berish o'rtasidagi kelishuvni anglatadi tarmoqli kengligi video uchun (va shu sababli qoniqarli rasm o'lchamlari) va mavjud kanallarni mavjud chastota diapazoniga to'ldirishga imkon beradi. Amalda deb nomlangan texnika vestigial yon tasma kanal oralig'ini kamaytirish uchun ishlatiladi, agar sof AM ishlatilsa video o'tkazuvchanlik kengligidan qariyb ikki baravar ko'p bo'ladi.

Signalni qabul qilish har doim a orqali amalga oshiriladi superheterodin qabul qiluvchisi: birinchi bosqich a sozlovchi bu televizion kanalni tanlaydi va chastotani statsionarga o'tkazadi oraliq chastota (IF). Signal kuchaytirgich mikrovolt diapazonidan volt fraksiyalarigacha IF bosqichlariga qadar kuchaytirishni amalga oshiradi.

Ovoz chiqarib olish

Shu nuqtada IF signali videodan iborat tashuvchi signal bitta chastotada va tovush tashuvchisi belgilangan ofsetda. A demodulator video signalni tiklaydi. Xuddi shu demodulatorning chiqishida ofset chastotasida yangi chastotali modulyatsiyalangan ovoz tashuvchisi mavjud. 1948 yilgacha bo'lgan ba'zi to'plamlarda bu filtrlangan va taxminan 22 MGts chastotali IF ovozi asosiy ovoz signalini tiklash uchun FM demodulatoriga yuborilgan. Yangi to'plamlarda ofset chastotasidagi ushbu yangi tashuvchisi sifatida qolishga ruxsat berildi intercarrier ovoziva asosiy ovoz signalini tiklash uchun FM demodulatoriga yuborildi. Interkarer tovushining o'ziga xos bir afzalligi shundaki, old panelning ingichka sozlash tugmasi o'rnatilganda, ovoz chiqadi tashuvchining chastotasi sozlash bilan o'zgarmaydi, lekin yuqorida qayd etilgan ofset chastotasida qoladi. Binobarin, ovozni yo'qotmasdan rasmni sozlash osonroq.

Shunday qilib, FM tovush tashuvchisi keyinchalik demodulatsiya qilinadi, kuchaytiriladi va karnayni boshqarish uchun ishlatiladi. Kelgunga qadar NICAM va MTS tizimlar, televizion ovoz uzatmalari doimo monofonik edi.

Video signalining tuzilishi

Video tashuvchisi a berish uchun demodulatsiya qilingan kompozit video signal; bu yorqinlik, xrominans va sinxronizatsiya signallarini o'z ichiga oladi;^[5] kabi analog video qurilmalar tomonidan ishlatiladigan video signal formatiga o'xshashdir Videomagnitofonlar yoki Videokameralar. Shuni esda tutingki, odatdagi AM bilan taqqoslaganda chastotali signal modulyatsiyasi teskari yo'naltirilgan: minimal video signal darajasi maksimal tashuvchi amplituda bilan mos keladi va aksincha. Transmitterlar va qabul qiluvchilarning arzon narxlardagi ishlab chiqarish xarajatlariga mos keladigan yaxshi chiziqliligini (sodiqligini) ta'minlash uchun video tashuvchi hech qachon umuman o'chirilmaydi. 1948 yilda intercarrier ovozi ixtiro qilinganida, tashuvchini to'liq o'chirmaslik intercarrier ovozini iqtisodiy jihatdan amalga oshirishga imkon beradigan yon ta'sirga ega edi.

Ko'rsatilgan rasmning har bir satri yuqorida ko'rsatilgan signal yordamida uzatiladi. Xuddi shu asosiy format (asosan vaqtni belgilash va rangni kodlash bilan bog'liq kichik farqlar bilan) PAL uchun ishlatiladi, NTSC va SECAM televizion tizimlari. Monoxrom signal rang bilan bir xil, faqat diagrammada rangda ko'rsatilgan elementlar mavjud emas (rang yorilishi va xrominans signali).

PAL video signalining bir qismi. Chapdan o'ngga: videoning oxiri ko'rish chizig'i, gorizontal orqa ayvon sinxronizatsiya pulsi, old peshayvon bilan rang portlashi va keyingi satrning boshi

The oldingi ayvon qisqacha (taxminan 1,5.) mikrosaniyadagi ) har bir uzatilgan rasm chizig'ining oxiri va keyingi satrning old tomoni o'rtasida qo'shilgan davr sinxronizatsiya pulsi. Uning maqsadi ruxsat berish edi Kuchlanish eski televizorlarda stabillashadigan darajalar, rasm chiziqlari orasidagi shovqinlarning oldini olish. The oldingi ayvon ning birinchi komponentidir gorizontal bo'shliq oralig'i gorizontal sinxronlash pulsini va orqa ayvon.^[6][7]

The orqa ayvon gorizontal sinxronlash pulsining oxiri (ko'tarilgan qirrasi) va faol videoning boshlanishi orasidagi har bir skanerlash chizig'ining qismi. Analog videoda qora darajadagi (300 mV) mos yozuvlarni tiklash uchun foydalaniladi. Signalni qayta ishlash shartlarida, bu kompensatsiyani kuz vaqti va joylashish vaqti sinxronizatsiya pulsidan so'ng.^[6][7]

PAL va NTSC kabi rangli televizion tizimlarda ushbu davrga quyidagilar kiradi rang portlashi signal. SECAM tizimida u nol rangli ma'lumotnomani o'rnatish uchun har bir ketma-ket rang farqi signali uchun mos yozuvlar subcarrierini o'z ichiga oladi.

Ba'zi professional tizimlarda, xususan sun'iy yo'ldosh aloqalari ikkinchi kanalni ijaraga olish xarajatlarini tejash uchun joylar o'rtasida audio video signalning orqa qismiga o'rnatilgan.

Monoxrom video signalni chiqarish

Kompozit video signalning yorqinligi komponenti "qora" darajadan 0 V dan 0,7 V gacha o'zgarib turadi. NTSC tizimida a mavjud bo'shatish old va orqa verandalarda ishlatiladigan signal darajasi va a qora undan 75 mV balandlikdagi signal darajasi; PAL va SECAM-da ular bir xil.

Monoxrom qabul qilgichda haydash uchun yorug'lik signallari kuchaytiriladi nazorat panjarasi ichida elektron qurol CRT. Bu elektron nurining intensivligini va shuning uchun skaner qilinayotgan joyning yorqinligini o'zgartiradi. Yorqinlik va kontrastni boshqarish mos ravishda doimiy o'zgarishni va kuchayishni aniqlaydi.

Rangli video signalni chiqarish

Rang paneli generatorining sinov signali

Rangli signal tasvirning qizil, yashil va ko'k qismlarining har biri uchun rasm ma'lumotlarini etkazib beradi (maqolaga qarang rang maydoni qo'shimcha ma'lumot olish uchun). Biroq, bu shunchaki uchta alohida signal sifatida uzatilmaydi, chunki: bunday signal monoxrom qabul qiluvchilarga mos kelmaydi (rangli eshittirish birinchi marta boshlanganda muhim ahamiyatga ega). Shuningdek, u mavjud televizorlarning o'tkazuvchanligini uch baravar ko'p egallaydi va mavjud televizion kanallar sonini kamaytirishni talab qiladi. Bundan tashqari, signal uzatilishidagi odatdagi muammolar (masalan, turli xil ranglarning turli xil qabul qilingan signal darajalari) noxush yon ta'sirga olib keladi.

Buning o'rniga, RGB signallari aylantiriladi YUV shakl, bu erda Y signali tasvirdagi ranglarning engilligini va qorong'iligini (yorqinligini) aks ettiradi. Ranglarni shu tarzda ko'rsatish qora va oq (monoxrom) plyonka va qora va oq (monoxrom) televizion tizimlarning maqsadi bo'lganligi sababli, Y signali yorug'lik signallari sifatida uzatish uchun juda mos keladi. Bu monoxrom qabul qiluvchining to'g'ri rasmni oq va oq rangda namoyish etishini ta'minlaydi, bu erda berilgan rang asl rangning qanchalik ochiq yoki qorong'i ekanligini to'g'ri aks ettiradigan kulrang soyada hosil bo'ladi.

U va V signallari "rang farqi" signallari. U signali - bu B signali va Y signali o'rtasidagi farq, shuningdek B minus Y (BY) deb nomlanadi va V signali - R signali va Y signali o'rtasidagi farq, shuningdek R minus Y (RY) . U signali keyinchalik "binafsha-ko'k" yoki uni to'ldiruvchi "sarg'ish-yashil" rangning rangini, V signal esa "binafsha-qizil" yoki uni to'ldiruvchi "yashil-ko'k" rangni bildiradi. Ushbu sxemaning afzalligi shundaki, rasm rang tarkibiga ega bo'lmaganida U va V signallari nolga teng. Inson ko'zi yorqinlikdagi tafsilotlarga rangdan ko'ra ko'proq sezgir bo'lgani uchun U va V signallari nisbatan nisbatan uzatilishi mumkin yo'qotish (xususan: tarmoqli kengligi cheklangan) qabul qilinadigan natijalarga ega usul.

Qabul qilgichda bitta demodulator U plyus V ning qo'shimcha birikmasini chiqarishi mumkin. Masalan, X / Z demodulyatsiya tizimida ishlatiladigan X demodulator. Xuddi shu tizimda, ikkinchi demodulator Z demodulator ham U plyus V ning qo'shimchali birikmasini chiqaradi, ammo boshqa nisbatda. X va Z rang farqlari signallari yana uchta rang farqi signallari (R-Y), (B-Y) va (G-Y) ga matritsalangan. Odatda ikkita, lekin ba'zan uchta demodulatorning kombinatsiyasi quyidagilar edi:

Oxir-oqibat, yuqoridagi rang farqlari signallarini c orqali f orqali matritsalash natijasida uchta rang farqi signallari (R-Y), (B-Y) va (G-Y) paydo bo'ldi.

Displey qurilmasi uchun zarur bo'lgan qabul qilgichdagi R, G, B signallari (CRT, plazma displey yoki LCD displey) elektron tarzda matritsalash yo'li bilan quyidagicha olinadi: R - (RY) ning Y bilan qo'shimchalar birikmasi, G - qo'shimchalar birikmasi ning (GY) ning Y bilan va B ning (BY) ning Y bilan qo'shimchali birikmasi. Bularning barchasi elektron shaklda amalga oshiriladi. Ko'rinib turibdiki, birlashtirish jarayonida Y signallarining past aniqlikdagi qismi bekor qilinadi va R, G va B signallari past aniqlikdagi tasvirni to'liq rangda ko'rsatishga qodir. Biroq, Y signallarining yuqori aniqlikdagi qismlari bekor qilinmaydi va shuning uchun ham R, G va B da mavjud bo'lib, monoxromda yuqori aniqlikdagi (yuqori aniqlikdagi) tasvir detallarini hosil qiladi, garchi u inson ko'ziga to'liq rangli va to'liq o'lchamdagi rasm.

Video signal bilan aralashtirilgan rangli signallar (ketma-ket ikkita gorizontal chiziq)

NTSC va PAL rang tizimlarida U va V yordamida uzatiladi kvadrati amplituda modulyatsiyasi subcarrierning. Ushbu modulyatsiya ikkita mustaqil signalni bitta subcarrier-ga qo'llaydi, chunki ikkala signal ham qabul oxirida mustaqil ravishda tiklanadi. Etkazib berishdan oldin, subcarrier o'zi videoning faol (ko'rinadigan) qismidan olib tashlanadi va portlash shaklida gorizontal bo'shliq qismiga ko'chiriladi, bu ekranda to'g'ridan-to'g'ri ko'rinmaydi. (Quyidagi portlash haqida ko'proq ma'lumot.)

NTSC uchun subcarrier 3,58 MGts sinus to'lqinidir. PAL tizimi uchun bu 4.43 MGts sinus to'lqinidir. Yuqorida aytib o'tilgan to'rtburchak amplituda subcarrier modulyatsiyasidan so'ng, subcarrier yonbosh lentalari ishlab chiqariladi va subcarrier o'zi videoning ko'rinadigan qismidan filtrlanadi, chunki u U va V ma'lumotlarining hammasi va subcarrier yon polosalari va subcarrier o'zi ma'lumot bermaydi.

Natijada paydo bo'lgan subcarrier yonbosh lentalari "xroma" yoki "xrominans" deb ham nomlanadi. Jismoniy jihatdan, bu xrominans signali 3,58 MGts (NTSC) yoki 4,43 MGts (PAL) sinus to'lqinidir, u o'zgaruvchan U va V qiymatlariga javoban fazani pastki tashuvchiga nisbatan o'zgartiradi va amplituda o'zgaradi.

Ma'lum bo'lishicha, xrom amplituda (Y signali bilan birgalikda ko'rib chiqilganda) rangning taxminiy to'yinganligini anglatadi va mos yozuvlar sifatida subcarrier-ga qarshi xrom fazasi rang rangini anglatadi. Sinov rang satrida aniqlangan test ranglari uchun ba'zida aniq amplituda va fazalar faqat sinov va muammolarni tuzatish maqsadida aniqlanadi.

U va V qiymatlarining o'zgarishiga javoban xrom sinus to'lqinlari subcarrierga nisbatan fazani o'zgartiradi, ammo subcarrier shunchaki "faz modulyatsiya qilingan" deb aytish to'g'ri emas. Buning sababi shundaki, QAM bilan bitta sinus to'lqin U sinov signali faqat bitta juft yonboshchani hosil qiladi, shu bilan bir xil sinov sharoitida haqiqiy fazali modulyatsiya ko'proq chastota spektrini egallaydigan bir nechta yonbosh tasmalarini hosil qiladi.

NTSCda xrominans sinus to'lqini subcarrier chastotasi bilan bir xil o'rtacha chastotaga ega. Ammo spektr analizatori vositasi shuni ko'rsatadiki, uzatiladigan xrominans uchun subcarrier chastotasidagi chastota komponenti aslida nol energiyaga teng bo'lib, subcarrier uzatilishidan oldin haqiqatan ham olib tashlanganligini tasdiqlaydi.

Ushbu yon tasma chastotalari yorug'lik signallari diapazoniga kiradi, shuning uchun ularni oddiygina "tashuvchi" yon chiziqlar o'rniga "subcarrier" yonboshlar deb atashadi. Ularning aniq chastotalari shunday tanlangan (NTSC uchun), ular ramkaning takrorlanish tezligining ikkita harmonikasi o'rtasida bo'lib, shu bilan yorug'lik signalining kuchining katta qismi xrominans signalining kuchiga to'g'ri kelmasligini ta'minlaydi.

Britaniyaning PAL (D) tizimida bir xil pastki va yuqori yon bantlar bilan haqiqiy xrominans markazining chastotasi 4.43361875 MGts ni tashkil etadi, bu skanerlash chastotasining to'g'ridan-to'g'ri ko'paytmasi. Ushbu chastota uzatilgan rasmda yuqori rang bilan to'yingan joylarda ko'rinadigan xrominans urish interferentsiyasi modelini minimallashtirish uchun tanlangan.

Ma'lum vaqtlarda xrominans signali faqat U signalini, 70 nanosekundadan (NTSC) keyinroq xrominans signali faqat V signalini ifodalaydi. (Bu xrominans signalini yaratgan kvadrati amplituda modulyatsiya jarayonining tabiati.) Keyinchalik 70 nanosekundada, -U va yana 70 nanosekundda, -V.

Shunday qilib, U ni olish uchun sinxron demodulator ishlatiladi, u har 280 nanosekundada xromni qisqacha eshitish (namuna) uchun subcarrier-dan foydalanadi, shunda chiqish faqat diskret impulslar poezdidir, ularning har biri amplituda asl nusxaga teng Tegishli vaqtda U signali. Aslida, bu impulslar U signalining diskret vaqtli analog namunalari. So'ngra impulslar past chastotali filtrdan o'tkaziladi, shunda asl analog doimiy uzluksiz U signali tiklanadi. V uchun 90 gradusgacha siljigan subcarrier har 280 nanosekundada xrom signalini qisqa vaqt ichida uzatadi va jarayonning qolgan qismi U signali uchun ishlatiladigan bilan bir xil bo'ladi.

Yuqorida aytib o'tilgan vaqtlardan boshqa har qanday vaqtda eshik ochish U, V, -U yoki -V har qanday ikkitasining qo'shimchali aralashmasini hosil qiladi. Ushbu "eksa tashqarisidagi" (ya'ni U va V o'qining) eshiklarini kiritish usullaridan biri I / Q demodulatsiyasi deb ataladi. Yana bir mashhur "o'qdan tashqari" sxemasi X / Z demodulyatsiya tizimi edi. Keyinchalik matritsalash asl U va V signallarini tikladi. Ushbu sxema aslida 60-yillar davomida eng mashhur demodulator sxemasi bo'lgan.

Yuqoridagi jarayonda subcarrier ishlatiladi. Ammo ilgari aytib o'tilganidek, u uzatilishdan oldin o'chirilgan va faqat xrom uzatiladi. Shuning uchun, qabul qilgich subcarrierni qayta tiklashi kerak. Shu maqsadda, har bir skanerlash chizig'ining orqa qismida (bo'shliqning qayta tiklanishi davrida) rang portlashi deb ataladigan subcarrierning qisqa portlashi uzatiladi. Qabul qilgichdagi subkariyer osilatori ushbu signalga qulflanadi (qarang fazali qulflangan pastadir ) o'zgarishlar moslamasiga erishish uchun, natijada osilator qayta tiklangan pastki tashuvchini ishlab chiqaradi.

(Qabul qiluvchilarning qimmatroq yoki yangi modellarida portlashning ikkinchi ishlatilishi - qabul qilishda xrom etishmovchiligini qoplash uchun AGC tizimiga havola.)

Sinov kartasi ko'rsatmoqda "Gannover barlari "(ranglarni tasma bosqichi effekti) Pal S (oddiy) signal uzatish rejimida.

NTSC ushbu jarayonni o'zgartirilmagan holda ishlatadi. Afsuski, bu tez-tez qabul qilingan signaldagi o'zgarishlar xatolari tufayli ranglarning yomon ko'payishiga olib keladi, ba'zida ko'p yo'lli, lekin asosan studiya oxirida yomon amalga oshiriladi. Havodagi analog signalga aylantirish uchun qattiq holatdagi qabul qiluvchilar, kabel televideniesi va raqamli studiya uskunalari paydo bo'lishi bilan ushbu NTSC muammolari asosan tuzatildi va operatorning xatoligi studiya oxirida qoldirilib, ranglarning namoyish etilishining zaifligi NTSC tizimi. Qanday bo'lmasin, PAL D (kechikish) tizimi asosan har bir ketma-ket chiziqdagi signal fazasini teskari yo'naltirish va natijalarni juft chiziqlar bo'yicha o'rtacha hisoblash yo'li bilan ushbu turdagi xatolarni tuzatadi. Ushbu jarayon 1H (bu erda H = gorizontal ko'rish chastotasi) davomiyligini kechiktirish chizig'idan foydalanish orqali erishiladi. (Ushbu qurilma bilan ishlatiladigan odatdagi sxema past chastotali rangli signalni o'zgartiradi ultratovush va yana qaytib). Shuning uchun ketma-ket chiziqlar orasidagi o'zgarishlar siljishidagi xatolar bekor qilinadi va kerakli faza amplitudasi ikki fazali (tasodif ) signallari qayta birlashtiriladi.

NTSC PALga qaraganda ancha samarali spektrga ega bo'lib, ma'lum bir tarmoqli kengligi uchun ko'proq rasm tafsilotlarini beradi. Buning sababi shundaki, qabul qilgichlardagi murakkab taroqli filtrlar NTSC-ning 4 ta maydon rangli faza kadansi bilan PAL-ning 8 ta dalaga nisbatan samaraliroq. Biroq, oxir-oqibat Evropadagi PAL tizimlarining katta kanal kengligi PAL tizimlariga ko'proq rasm tafsilotlarini uzatishda yordam beradi.

In SECAM televizor tizimi, U va V uzatiladi muqobil chiziqlardan foydalanib, oddiy chastota modulyatsiyasi ikki xil rang subcarrier.

1956 yildan boshlab ba'zi bir analog rangli CRT displeylarida nashrida signalini boshqarish (nashrida ) ga beriladi katod elektron qurollarning ulanishlari va rang farqi signallari (xrominans signallari) boshqaruv tarmoqlari ulanishlariga beriladi. Ushbu oddiy CRT matritsasini aralashtirish texnikasi keyinchalik o'zgartirildi qattiq holat 1954 va 1955 yillarda rangli televizion qabul qiluvchilarda ishlatilgan asl matritsalash usuli bilan signallarni qayta ishlash konstruktsiyalari.

Sinxronizatsiya

Har birining oxirida video signalga qo'shilgan sinxronizatsiya impulslari ko'rish chizig'i va video kadr qabul qilgichdagi supurish osilatorlarining uzatilgan signal bilan bir qadamda qulflanib turishini ta'minlaydi, shunda tasvir qabul qilgich ekranida qayta tiklanishi mumkin.^[6][7][8]

A sinxronizator elektron sinxronlash kuchlanish darajasini aniqlaydi va impulslarni gorizontal va vertikal sinxronlashtirishga ajratadi.

Landshaft sinxronizatsiya

Gorizontal sinxronizatsiya impulsi (gorizontal sinxronizatsiya, yoki HSync), ajratib turadi skanerlash chiziqlari. Gorizontal sinxronizatsiya signali - bu har bir chiziqning boshlanishini ko'rsatadigan bitta qisqa puls. Qolgan skanerlash liniyasi quyidagicha, signal 0,3 V (qora) dan 1 V (oq) gacha, keyingi gorizontalgacha yoki vertikal sinxronizatsiya pulsi.

Gorizontal sinxronlash pulsining formati turlicha. 525 qatorda NTSC tizim bu 4.85ms - uzoq puls 0 daV. 625 qatorda PAL tizim pulsi 4,7 mk sinxronizatsiya pulsi 0 ga tengV . Bu har qanday video signal amplitudasidan past (qora rangdan qora) shuning uchun uni qabul qiluvchining darajasiga sezgir bo'lgan "sinxronlashtiruvchi" sxemasi orqali aniqlash mumkin.

Vertikal sinxronizatsiya

Vertikal sinxronizatsiya (vertikal sinxronlash yoki VSync deb ham yuritiladi) video maydonlarni ajratib turadi. PAL va NTSC da vertikal sinxronlash impulsi ichida bo'ladi vertikal bo'shliq oralig'i. Vertikal sinxronizatsiya impulslari HSYNC impulslarining uzunligini skanerlash chizig'ining deyarli butun uzunligi bo'ylab uzaytirish orqali amalga oshiriladi.

The vertikal sinxronizatsiya signal - bu yangi maydonning boshlanishini ko'rsatadigan ancha uzunroq zarbalar seriyasidir. Sinxronizatsiya impulslari skanerlashning boshida va oxirida bir qator qatorlarning butun oralig'ini egallaydi; vertikal orqaga qaytish paytida rasm haqida ma'lumot uzatilmaydi. Impuls ketma-ketligi vertikal orqaga qaytish paytida gorizontal sinxronlashni davom ettirish uchun mo'ljallangan; shuningdek, har bir maydon interlaced tizimlarda juft yoki toq chiziqlarni anglatadimi (gorizontal chiziq boshlanishidan yoki o'rtada boshlanishiga qarab).

525 qatorli bunday signal formati NTSC bu:

• oldindan tenglashtiruvchi impulslar (6 ta toq chiziqlarni skanerlashni boshlash uchun, 5 ta juft chiziqlarni skanerlashni boshlash uchun)
• uzoq muddatli sinxronizatsiya (5 ta impuls)
• tenglashtirishdan keyingi impulslar (5 ta toq chiziqlarni skanerlashni boshlash uchun, 4 ta juft chiziqlarni skanerlashni boshlash uchun)

Tenglashdan oldingi yoki keyin har bir zarba yarimdan iborat ko'rish chizig'i qora signal: 0 Vda 2 mk, undan keyin 0,3 Vda 30 mk.

Har bir uzoq sinxronlash pulsi vaqtlari teskari bo'lgan tenglashtiruvchi impulsdan iborat: 0 V da 30 mk, undan keyin 0,3 Vda 2 mk.

Video ishlab chiqarishda va kompyuter grafikalarida tasvirdagi uzilishlar tez-tez ko'rinadigan uzilishlardan saqlanish uchun vertikal sinxronizatsiya impulsi bilan bir qatorda saqlanadi. Beri ramka buferi a kompyuter grafikasi displey katod-ray displeyining dinamikasini taqlid qiladi, agar u tasvir displeyga uzatilayotganda yangi rasm bilan yangilansa, displeyda ikkala freymning mishmash-si paydo bo'lib, sahifani yirtib tashlash artefakt tasvirning bir qismini pastga tushiring.

Vertikal sinxronizatsiya bu bilan vaqt oralig'idagi tampon to'ldirish vaqtini belgilaydi vertikal bo'shliq oralig'i Shunday qilib, ekranda faqat butun kadrlar ko'rinishini ta'minlaydi. Video o'yinlar va kabi dasturiy ta'minot kompyuter yordamida loyihalash (SAPR) paketlar ko'pincha vertikal sinxronizatsiyani variant sifatida beradi, chunki u rasmni yangilashni vertikal bo'shliq oralig'igacha kechiktiradi. Bu kechikish vaqtida kichik jazoni keltirib chiqaradi, chunki dastur videoni boshqaruvchisi tasvirni displeyga uzatishni tugatguncha kutishdan oldin davom etishi kerak. Uch marta buferlash bu kechikishni sezilarli darajada kamaytiradi.

Ikkala vaqt oralig'i aniqlangan - the oldingi ayvon ko'rsatilgan videoning oxiri va sinxronizatsiya pulsining boshlanishi o'rtasida va orqa ayvon sinxronlash pulsidan keyin va ko'rsatilgan videodan oldin. Bular va sinxronlash impulsining o'zi "deb nomlanadi gorizontal bo'shliq (yoki takrorlash) oraliq va CRT-dagi elektron nuri keyingi displey chizig'ining boshlanishiga qaytish vaqtini aks ettiradi.

Gorizontal va vertikal ushlash

Analog televizion qabul qiluvchilar va kompozit monitorlar ko'pincha gorizontal va vertikal vaqtni sozlash uchun qo'lda boshqarishni ta'minlaydi.

O'tkazgich (yoki burilish) osilatorlari televizion stantsiyadan (yoki VCR, kompyuter yoki boshqa kompozit video manbadan) signalsiz ishlashga mo'ljallangan edi. Bu bugungi monitorlardagi "CHECK SIGNAL CABLE" xabarlariga o'xshash bo'sh tuvalni taqdim etadi: televizor qabul qiluvchisiga to'plamning eng asosiy zanjirlarining asosiy ishlashini tasdiqlash uchun rasterni ko'rsatish va antennani joylashtirish paytida tasvirni taqdim etishga imkon berish. . Signalning etarlicha kuchliligi bilan qabul qiluvchining sinxronlashtiruvchi ajratuvchi davri kelib tushgan videodan vaqt bazasi impulslarini ajratib, ularni gorizontal va vertikal osilatorlarni stantsiyadan kelgan signal bilan sinxronlashtirish uchun mos vaqtda tiklashda ishlatadi.

Gorizontal zanjirning erkin ishlaydigan tebranishi juda muhimdir, chunki gorizontal burilish davrlari odatda flyback transformatorini (CRT uchun tezlashuv potentsialini ta'minlaydi), shuningdek, yuqori voltli rektifikator trubkasi uchun iplarni va ba'zan filaman (lar) ni quvvatlantiradi. CRTning o'zi. Gorizontal osilator va chiqish bosqichlari ishlamasdan, 1940-yillardan beri deyarli har qanday analog televizion qabul qiluvchilar uchun CRT yuzining yoritilishi mutlaqo bo'lmaydi.

Dastlabki televizion qabul qilgichlarda vaqtni aniq belgilash komponentlarining etishmasligi vaqt bazasi zanjirlari vaqti-vaqti bilan qo'lda sozlashni talab qilar edi, agar ularning erkin ishlaydigan chastotalari haqiqiy chiziq va maydon stavkalaridan juda uzoq bo'lsa, zanjirlar kiruvchi sinxronizatsiya signallarini kuzatib bo'lmaydi. Gorizontal sinxronizatsiyani yo'qotish odatda tomosha qilinmaydigan rasmga olib keldi; vertikal sinxronizatsiyani yo'qotish tasvirni ekranda yuqoriga yoki pastga aylantiradi.

Sozlash shaklini oldi gorizontal ushlash va vertikal ushlash boshqaruv elementlari, odatda old panelda boshqa umumiy boshqaruv elementlari bilan birga. Ular mos keladigan vaqt bazasi osilatorlarining erkin ishlaydigan chastotalarini moslashtirdilar.

To'g'ri ishlash, gorizontal yoki vertikal ushlashni sozlash suratning ekranda deyarli o'z joyiga tushishiga olib kelishi kerak; bu deyiladi sinxronlash qulfi. A slowly rolling vertical picture demonstrates that the vertical oscillator is nearly synchronized with the television station but is not locking to it, often due to a weak signal or a failure in the sync separator stage not resetting the oscillator. Sometimes, the black interval bar will almost stop at the right place, again indicating a fault in sync separation is not properly resetting the vertical oscillator.

Horizontal sync errors cause the image to be torn diagonally and repeated across the screen as if it were wrapped around a screw or a barber's pole; the greater the error, the more "copies" of the image will be seen at once wrapped around the barber pole. Given the importance of the horizontal sync circuit as a power supply to many subcircuits in the receiver, they may begin to malfunction as well; and horizontal output components that were designed to work together in a resonant circuit may become damaged.

In the earliest electronic television receivers (1930s-1950s), the time base for the sweep oscillators was generally derived from RC circuits based on carbon resistors and paper capacitors. After turning on the receiver, the vacuum tubes in the set would warm up and the oscillators would begin to run, allowing a watchable picture. Resistors were generally simple pieces of carbon inside a Bakelite enclosure, and the capacitors were usually alternating layers of paper and aluminum foil inside cardboard tubes sealed with bee's wax. Moisture ingress (from ambient air humidity) as well as thermal instability of these components affected their electrical values. As the heat from the tubes and the electrical currents passing through the RC circuits warmed them up, the electrical properties of the RC timebase would shift, causing the oscillators to drift in frequency to a point that they could no longer be synchronized with the received pulses coming from the TV station via the sync separator circuit, causing tearing (horizontal) or rolling (vertical).

Hermetically-sealed passive components and cooler-running semiconductors as active components gradually improved reliability to the point where the horizontal hold was moved to the rear of the set first, and the vertical hold control (due to the longer period in the RC constant) persisted as a front panel control well into the 1970s as the consistency of larger-value capacitors increased.

By the early 1980s the efficacy of the synchronization circuits, plus the inherent stability of the sets' oscillators, had been improved to the point where these controls were no longer necessary. Integrated Circuits which eliminated the horizontal hold control were starting to appear as early as 1969.^[9]

The final generations of analog television receivers (most TV sets with internal on-screen displays to adjust brightness, color, tint, contrast) used "TV-set-on-a-chip" designs where the receiver's timebases were divided down from crystal oscillators, usually based on the 3.58 MHz NTSC colorburst reference. PAL and SECAM receivers were similar though operating at different frequencies. With these sets, adjustment of the free-running frequency of either sweep oscillator was either physically impossible (being derived inside the integrated circuit) or possibly through a hidden service mode typically offering only NTSC/PAL frequency switching, accessible through the On-Screen Display's menu system.

Horizontal and Vertical Hold controls were rarely used in CRT-based computer monitors, as the quality and consistency of components were quite high by the advent of the computer age, but might be found on some composite monitors used with the 1970s-1980s home or personal computers.

There is no equivalent in modern television systems.

Other technical information

Components of a television system

A typical analog monochrome televizion qabul qilgich is based around the block diagram shown below:

The tuner is the object which "plucks" the television signals out of the air, with the aid of an antenna. There are two types of tuners in analog television, VHF va UHF tuners. The VHF tuner selects the VHF television frequency. This consists of a 4 MHz video bandwidth and a 2 MHz audio bandwidth. It then amplifies the signal and converts it to a 45.75 MHz O'rta chastota (IF) amplitude-modulated picture and a 41.25 MHz IF frequency-modulated audio carrier.

The IF amplifiers are centered at 44 MHz for optimal frequency transference of the audio and frequency carriers. What centers this frequency is the IF transformer. They are designed for a certain amount of bandwidth to encompass the audio and video. It depends on the number of stages (the amplifier between the transformers). Most of the early television sets (1939–45) used 4 stages with specially designed video amplifier tubes (the type 1852/6AC7). In 1946 the RCA presented a new innovation in television; the RCA 630TS. Instead of using the 1852 octal tube, it uses the 6AG5 7-pin miniature tube. It still had 4 stages, but it was 1/2 the size. Soon all of the manufactures followed RCA and designed better IF stages. They developed higher amplification tubes, and lower stage counts with more amplification. When the tube era came to an end in the mid-70s, they had shrunk the IF stages down to 1-2 (depending on the set) and with the same amplification as the 4 stage, 1852 tube sets. Like radio, television has Avtomatik daromadni boshqarish (AGC). This controls the gain of the IF amplifier stages and the tuner. More of this will be discussed below.

The video amp and output amplifier consist of a low linear pentod or a high powered transistor. The video amp and output stage separate the 45.75 MHz from the 41.25 MHz. It simply uses a diode to detect the video signal. But the frequency-modulated audio is still in the video. Since the diode only detects AM signals, the FM audio signal is still in the video in the form of a 4.5 MHz signal. There are two ways to attach this problem, and both of them work. We can detect the signal before it enters into the video amplifier, or do it after the audio amplifier. Many television sets (1946 to late 1960s) used the after video amplification method, but of course, there is the occasional exception. Many of the later set late (1960s-now) use the before-the-video amplifier way. In some of the early television sets (1939–45) used its own separate tuner, so there was no need for a detection stage next to the amplifier. After the video detector, the video is amplified and sent to the sync separator and then to the picture tube.

At this point, we will now look at the audio section. The means of detection of the audio signal is by a 4.5 MHz traps coil/transformer. After that, it then goes to a 4.5 MHz amplifier. This amplifier prepares the signal for the 4.5Mhz detector. It then goes through a 4.5 MHz IF transformer to the detector. In television, there are 2 ways of detecting FM signals. One way is by the nisbat detektori. This is simple but very hard to align. The next is a relatively simple detector. Bu to'rtburchak detektori. It was invented in 1954. The first tube designed for this purpose was the 6BN6 type. It is easy to align and simple in circuitry. It was such a good design that it is still being used today in the Integrated circuit form. After the detector, it goes to the audio amplifier.

The next part is the sync separator/clipper. This also does more than what is in its name. It also forms the AGC voltage, as previously stated. This sync separator turns the video into a signal that the Horizontal and Vertical oscillators can use to keep in sync with the video.

The horizontal and vertical oscillators form the raster on the CRT. They are kept in sync by the sync separator. There are many ways to create these oscillators. The first one is the earliest of its kind is the tiratron osilator. Although it is known to drift, it makes a perfect sawtooth wave. This sawtooth wave is so good that no linearity control is needed. This oscillator was for the electrostatic deflection CRTs. It found some purpose for the electromagnetically deflected CRTs. The next oscillator is the blocking oscillator. It uses a transformer to create a sawtooth wave. This was only used for a brief time period and never was very popular after the beginning. The next oscillator is the multivibrator. This oscillator was probably the most successful. It needed more adjustment than the other oscillators, but it is very simple and effective. This oscillator was so popular that it was used from the early 1950s till today.

The oscillator amplifier is sorted into two categories. The vertical amplifier directly drives the yoke. There is not much to this. It is similar to an audio amplifier. The horizontal oscillator is a different situation. The oscillator must supply the high voltage and the yoke power. This requires a high power flyback transformer, and a high powered tube or transistor. This is a problematic section for CRT televisions because it has to handle high power.

Sync separator

Portion of a PAL videosignal. From left to right: end of a video line, front porch, horizontal sync pulse, back porch with rang portlashi, and beginning of next line

Beginning of the frame, showing several scan lines; the terminal part of the vertical sync pulse is at the left

PAL video signal frames. Left to right: frame with scan lines (overlapping together, horizontal sync pulses show as the doubled straight horizontal lines), vertical blanking interval with vertical sync (shows as brightness increase of the bottom part of the signal in almost the leftmost part of the vertical blanking interval), entire frame, another VBI with VSYNC, beginning of the third frame

Image synchronization is achieved by transmitting negative-going pulses; in a composite video signal of 1-volt amplitude, these are approximately 0.3 V below the "qora daraja " horizontal sync signal is a single short pulse which indicates the start of every line. Two-timing intervals are defined – the front porch between the end of the displayed video and the start of the sync pulse, and the back porch after the sync pulse and before the displayed video. These and the sync pulse itself are called the horizontal blanking (yoki retrace) oraliq and represent the time that the electron beam in the CRT is returning to the start of the next display line.

The vertical sync signal is a series of much longer pulses, indicating the start of a new field. The sync pulses occupy the whole of line interval of a number of lines at the beginning and end of a scan; no picture information is transmitted during vertical retrace. The pulse sequence is designed to allow horizontal sync to continue during vertical retrace; it also indicates whether each field represents even or odd lines in interlaced systems (depending on whether it begins at the start of a horizontal line, or midway through).

In the television receiver, a sync separator circuit detects the sync voltage levels and sorts the pulses into horizontal and vertical sync.

Loss of horizontal synchronization usually resulted in an unwatchable picture; loss of vertical synchronization would produce an image rolling up or down the screen.

Counting sync pulses, a video line selector picks a selected line from a TV signal, used for telematn, ekrandagi displeylar, stantsiyani identifikatsiyalash logos as well as in the industry when cameras were used as a sensor.

Timebase circuits

In an analog receiver with a CRT display sync pulses are fed to horizontal and vertical timebase circuits (commonly called "sweep circuits" in the United States), each consisting of an oscillator and an amplifier. These generate modified arra tishlari va parabola current waveforms to scan the electron beam in a chiziqli yo'l. The waveform shapes are necessary to make up for the distance variations from the electron beam source and the screen surface. The oscillators are designed to free-run at frequencies very close to the field and line rates, but the sync pulses cause them to reset at the beginning of each scan line or field, resulting in the necessary synchronization of the beam sweep with the originating signal. The output waveforms from the timebase amplifiers are fed to the horizontal and vertical deflection coils wrapped around the CRT tube. These coils produce magnit maydonlari proportional to the changing current, and these deflect the electron beam across the screen.

In the 1950s, the power for these circuits was derived directly from the mains supply.A simple circuit consisted of a seriyali voltage dropper qarshilik va a rektifikator vana (naycha ) yoki yarim o'tkazgich diyot. This avoided the cost of a large high voltage mains supply (50 or 60 Hz) transformator. This type of circuit was used for the thermionic valve (vakuum trubkasi ) texnologiya. It was inefficient and produced a lot of heat which led to premature failures in the circuitry. Although failure was common, it was easily repairable.

1960-yillarda, yarim o'tkazgich technology was introduced into timebase circuits. During the late 1960s in the UK, sinxron (with the scan line rate) power generation was introduced into qattiq holat qabul qilgich dizayni.^[10] These had very complex circuits in which faults were difficult to trace, but had very efficient use of power.

1970-yillarning boshlarida AC mains (50 or 60 Hz), and line timebase (15,625 Hz), tiristor based switching circuits were introduced. In the UK use of the simple (50 Hz) types of power, circuits were discontinued. The reason for design changes arose from the electricity supply contamination problems arising from EMI,^[11] and supply loading issues due to energy being taken from only the positive half cycle of the mains supply waveform.^[12]

CRT flyback power supply

Most of the receiver's circuitry (at least in tranzistor - yoki TUSHUNARLI -based designs) operates from a comparatively low-voltage DC quvvatlantirish manbai. Biroq, anod connection for a katod-nurli naycha requires a very high voltage (typically 10–30 kV) for correct operation.

This voltage is not directly produced by the main quvvatlantirish manbai circuitry; instead, the receiver makes use of the circuitry used for horizontal scanning. To'g'ridan to'g'ri oqim (DC), is switched through the line output transformer, and o'zgaruvchan tok (AC) is induced into the scan coils. At the end of each horizontal scan line the magnit maydon, which has built up in both transformer and scan coils by the current, is a source of latent electromagnetic energy. This stored collapsing magnetic field energy can be captured. The reverse flow, short duration, (about 10% of the line scan time) current from both the line output transformer and the horizontal scan coil is discharged again into the birlamchi o'rash ning flyback transformatori by the use of a rectifier which blocks this negative reverse emf. A small value kondansatör is connected across the scan switching device. This tunes the circuit indüktanslar ga resonate at a much higher chastota. This slows down (lengthens) the flyback time from the extremely rapid decay rate that would result if they were electrically isolated during this short period. One of the secondary windings on the flyback transformer then feeds this brief high voltage pulse to a Cockcroft-Walton generatori dizayn kuchlanish multiplikatori. This produces the required EHT ta'minot. A flyback converter is a power supply circuit operating on similar principles.

A typical modern design incorporates the flyback transformer and rectifier circuitry into a single unit with a captive output lead, (known as a diode split line output transformer or an Integrated High Voltage Transformer (IHVT)),^[13] so that all high-voltage parts are enclosed. Earlier designs used a separate line output transformer and a well-insulated high voltage multiplier unit. The high frequency (15 kHz or so) of the horizontal scanning allows reasonably small components to be used.

Transition to digital

The first country to make a wholesale almashtirish to digital over-the-air (terrestrial television) broadcasting was Luxembourg in 2006, followed later in 2006 by the Netherlands; in 2007 by Finland, Andorra, Sweden and Switzerland; in 2008 by Belgium (Flanders) and Germany; in 2009 by the United States (high power stations), southern Canada, the Isle of Man, Norway, and Denmark. In 2010, Belgium (Wallonia), Spain, Wales, Latvia, Estonia, the Channel Islands, San Marino, Croatia, and Slovenia; in 2011 Israel, Austria, Monaco, Cyprus, Japan (excluding Miyagi, Ivate va Fukusima prefectures), Malta and France; in 2012 the Czech Republic, Arab World, Taiwan, Portugal, Japan (including Miyagi, Iwate, and Fukushima prefectures), Serbia, Italy, Canada, Mauritius, the United Kingdom, the Republic of Ireland, Lithuania, Slovakia, Gibraltar, and South Korea; in 2013, the Republic of Macedonia, Poland, Bulgaria, Hungary, Australia, and New Zealand, completed the transition. The United Kingdom made the transition to digital television between 2008 and 2012, with the exception of Furness-Barrow, which made the switch over in 2007. The first digital TV-only area in the United Kingdom was Ferryside in Karmartenshir.

The Qo'shma Shtatlarda raqamli televizion o'tish for high-powered transmission was completed on 12 June 2009, the date that the Federal aloqa komissiyasi (FCC) set. Almost two million households could no longer watch television because they had not prepared for the transition. The switchover had been delayed by the DTV-ni kechiktirish to'g'risidagi qonun.^[14] While the majority of the viewers of over-the-air broadcast television in the U.S. watch full-power stations (which number about 1800), there are three other categories of television stations in the U.S.: kam quvvatli eshittirish stantsiyalar, class A stations va television translator stations. They were given later deadlines. In broadcasting, whatever happens in the United States also influences southern Canada and northern Mexico because those areas are covered by television stations in the U.S.

In Japan, the switch to digital began in northeastern Ishikava prefekturasi on 24 July 2010 and ended in 43 of the country's 47 prefectures (including the rest of Ishikawa) on 24 July 2011, but in Fukusima, Ivate va Miyagi prefectures, the conversion was delayed to 31 March 2012, due to complications from the 2011 Txoku zilzilasi va tsunami va unga bog'liq bo'lgan yadroviy avariyalar.

In Canada, most of the larger cities turned off analog broadcasts on 31 August 2011.^[15]

China is scheduled to end analog broadcasting between 2015 and 2018.^{[iqtibos kerak ]}

Brazil switched to digital television on 2 December 2007 in its major cities. It is now estimated that Brazil will end analog broadcasting in 2023.^[16]

In Malaysia, the Malaysian Communications & Multimedia Commission (MCMC) advertised for tender bids to be submitted in the third quarter of 2009 for the 470 through 742 MHz UHF allocation, to enable Malaysia's broadcast system to move into DTV. Yangi translyatsiya guruhi allocation would result in Malaysia's having to build an infrastructure for all broadcasters, using a single digital terrestrial transmission /television broadcast (DTTB) channel.^{[iqtibos kerak ]} Large portions of Malaysia are covered by television broadcasts from Singapore, Thailand, Brunei, and Indonesia (from Borneo and Batam). Starting from 1 November 2019, all regions in Malaysia were no longer using the analog system after the states of Sabah and Sarawak finally turned it off on 31 October 2019.^[17]

In Singapore, digital television under DVB-T2 began on 16 December 2013. The switchover was delayed many times until analog TV was switched off at midnight on 2 January 2019.^{[iqtibos kerak ]}

Filippinda Milliy telekommunikatsiya komissiyasi required all broadcasting companies to end analog broadcasting on 31 December 2015 at 11:59 p.m. Due to delay of the release of the implementing rules and regulations for digital television broadcast, the target date was moved to 2020. Full digital broadcast is expected in 2021 and all of the analog TV services should be shut down by the end of 2023.^{[iqtibos kerak ]}

In the Russian Federation, the Rossiya televizion va radioeshittirish tarmog'i (RTRS) disabled analog broadcasting of federal channels in five stages, shutting down broadcasting in multiple federal sub'ektlar har bir bosqichda. The first region to have analog broadcasting disabled was Tver viloyati on 3 December 2018, and the switchover was completed on 14 October 2019.^[18] During the transition, DVB-T2 receivers and monetary compensations for purchasing of terrestrial or satellite digital TV reception equipment were provided to disabled people, World War II veterans, certain categories of retirees and households with income per member below living wage.^[19]

Shuningdek qarang

Adabiyotlar

Tashqi havolalar

• Video signal measurement and generation
• Television synchronisation
• Video broadcast standard frequencies and country listings
• EDN magazine describing design of a 1958 transistorised television receiver
• Designing the color television signal in the early 1950s as described by two engineers working directly with the NTSC