Raws li koj paub, lub xov tooj cua zaus teeb liab muaj cov cab kuj, uas yog raws li xov tooj cua emission nyob rau hauv daim ntawv ntawm ib tug yooj yim harmonic oscillation u (t)=U cos (ωt + φ). Nws ua raws los ntawm qhov no uas muaj peb qhov kev ywj pheej tsis muaj nyob rau hauv cov khoom siv zaus teeb liab, los ntawm kev ua rau nws muaj peev xwm ntes cov kev hloov pauv hauv cov teeb liab tswj.
Qhov no txhais tau tias muaj peb hom: amplitude (AM), zaus (FM) thiab theem kev hloov pauv (PM).
Phase modulation yog ib txoj hauv kev xa cov ntaub ntawv analog lossis cov ntaub ntawv digital los ntawm kev hloov lub kaum sab xis pib (theem) φ 0ntawm cov neeg nqa khoom zaus ntawm cov teeb liab kis.
Nrog nws, theem φ(t) nyob ntawm lub amplitude ntawm kev tswj (modulating) teeb liab, i.e. φ(t)=ω0 + Δφ∙sinΩt + φ0==φ0 + ke (t), qhov twg k yog qhov proportionality.
Ib theem-modulated teeb liab feem ntau piav qhia los ntawm kev qhia u (t)=Un sin [ωt + φ (t)].
Thaum modulating nrog ib lub suab [e (t)=E sin Ωt] peb muaj: φ(t)=φ0 + kE sin Ωt=φ 0 +Δφmaxsin Ωt.
Tom qab hloov tus nqi ntawm φ(t) rau hauv qhov sib npaug ntawm theem-modulated teeb liab, peb tau txais u (t)=Un sin (ω n t + φ0 + Δφmax sin Ωt), qhov twg Δφmax yog theem siab tshaj plaws hloov pauv hloov pauv mus rau amplitude ntawm kev tswj hluav taws xob. Δφmaxyog lwm yam hu ua angular modulation index thiab denoted los ntawm m.
Raws li koj pom, ntawm FM m=Δφmax =kE. Tus nqi tam sim ntawm lub sij hawm sib txawv ntawm lub kaum sab xis Θ (t) yog Θ (t)=ωn t + φ0 + msin Ωt, so ω=d Θ (t)/dt=ωn + mΩ cosΩt, where mΩ=ΔφmaxΩ=Δ ω n =kEΩ - qhov siab tshaj qhov sib txawv ntawm ωnntawm PM, ncaj qha proportional rau lub amplitude thiab zaus ntawm modulating oscillation.
Yog li, nrog PM, qhov ntsuas ntsuas ntsuas, uas qhia txog qhov hloov pauv siab tshaj plaws, yog proportional rau lub amplitude ntawm lub teeb liab tswj thiab tsis nyob ntawm qhov kev hloov pauv zaus. Qhov kev hloov pauv ntawm qhov sib txawv ntawm qhov nruab nrab tus nqi (kev sib txawv) hloov pauv ncaj qha mus rau qhov amplitude thiab zaus ntawm modulating voltage.
Nyob ntawm cov kev siv ntawm kev siv, theem kev hloov kho muaj ntau ntau yam. Ib qho ntawm lawv, tshwj xeeb, yog txheeb ze hloov pauv hloov pauv.
Nyob rau hauv daim ntawv no, nyob ntawm lub modulating teeb liab, tsuas yog theem ntawm lub teeb liab hloov, thiab zaus thiabamplitude tseem tsis hloov. Nrog OFM, cov ntaub ntawv tus nqi tsis yog qhov hloov pauv kiag li hauv theem, tab sis nws qhov kev hloov pauv txheeb ze rau tus nqi dhau los.
Lub voj voog hluav taws xob uas ua rau lub kaum sab xis ntawm lub voj voog hloov pauv (kwv yees rau cov cab kuj tsis hloov pauv) hloov pauv raws li cov teeb liab modulating hu ua theem modulator.
Ntau hom duab tau tsim. Ib qho yooj yim modulator Circuit Court muaj ib tug varicap - ib tug diode muaj peev xwm hloov lub hlws ris capacitance nyob rau hauv qhov kev txiav txim ntawm ib tug tswj voltage. Nyob rau hauv no Circuit Court, lub modulating voltage hloov lub capacitance ntawm lub varicap. Cov theem hloov nyob ntawm qhov txheeb ze tus nqi ntawm lub peev xwm ntawm lub diode no thiab cov load kuj R.
Yog li, qhov kev hloov pauv no nyob ntawm qhov ntsuas qhov ntsuas hluav taws xob. Qhov no yog dab tsi ua rau theem modulation ntawm lub xov tooj cua teeb liab. Txawm li cas los xij, xws li kev hloov pauv tsis yog-linearly cuam tshuam nrog kev hloov pauv hluav taws xob, lub peev xwm ntawm varicap tsis yog-linearly cuam tshuam nrog cov modulating voltage, uas tsim teeb meem ntxiv hauv kev tsim cov theem modulators.
Nyob hauv nws daim ntawv dawb huv, theem kev hloov pauv tsis tau siv dav vim nws qhov tsis zoo hauv qhov tsis zoo - tsis muaj suab nrov tiv thaiv.
