Pseudo- time base error correction circuit _1483

px477801

Pseudo-time base error correction circuit

Device (2) t mixer (1), another input is phase-locked oscillator locked by a continuous color burst signal, the frequency (k ± Af), it has the same frequency and color signal components ± △ f. Mixer (1) output signal of the frequency of continuous :'[(+ 1) r ± △ doors and [(H a 1J / thousand △] · Received a l2-24 1997 3 Li Wenxian other pseudo-time base columns with the error band-pass filter circuit device transition frequency component to obtain access and frequency of [(n-F1) fsc ± △ f] of the continuous signal. mixers (2) is the standard input of another sub-carrier, the output The frequency of continuous signals (+1) / and (a 1) c regulatory loop playback direct recording frequency f Principle and out with the band-pass filter frequency component to obtain a frequency of (n +1) of the continuous signal. will The continuous signal given away mixers (3 and sub-carrier frequency (f. + △ r) of the chroma signal mixer, mixer (3) output of the chroma signal carrier frequency :[() f ± △ /] and [, / _l (thousands of △,] out with a band pass filter and frequency components, the output subcarrier frequency of [(n ten 2) k ± △ f] of the chroma signal, the color mixer signal given away degrees (d) and the frequency of [(n +1) ± △ f] of the continuous signal mixer, mixer (4) output of the chroma signal carrier frequency is: [(2,2 +3) / ± 2 △ door and, with the difference frequency band-pass filters remove the component, so that can be caused by the jitter component color signal △ f frequency offset, and thus the output frequency stability of the chroma signal, the final and the luminance signal and then mixed to obtain a stable color video signal. 2. chroma down-conversion law principle recorded chrominance signal down-conversion method using pseudo-record time base correction circuit shown in Figure 2. in order to reduce record signal bandwidth, the quality of the video recorder in the middle down-conversion method is widely used in recording color signal, the playback method can not only use the pseudo-frequency time base error correction, but also complete up-to standard subcarrier frequency task. with a frequency change of chrominance signal components of lower frequency, the frequency of [k ± Af], put it into the mixer (1) and frequency of [k + f ± △ f] of the tape and then mixing with a reference signal Remove the difference frequency components pass filter, so that you can change the color signal components △ f the frequency offset, gain and phase stability in frequency and carrier frequency. 【.43 MHz chroma signal. Baoji University (Natural Science Edition) 1998 frequency [k + f ± △ f] tape reference signal output by the VCO frequency is [soil At3 signal and the machine from an external crystal oscillator or 4.43MHz (fsc) signal mixing, with the band pass filter and frequency components generated by removing the tape to the carrier frequency reference signal and the low frequency chrominance signals have the same change in composition △ f, VCO has two control loops, one said automatic phase control, an automatic frequency control circuit, said the former is closed, which is open loop. automatic phase control loop control voltage from the output color burst gating signal through the circuit, sending an excellent standard of sync with the 4.43MHz subcarrier phase to obtain, it makes the output chrominance signal carrier frequency stabilized at 4.43MHz, but when the low frequency carrier chrominance signal components of change is too large, will inevitably lead to excessive output chroma signal phase changes, and even can not lock . Automatic frequency control circuit is to increase the scope of automatic phase synchronization loop, reducing the output chroma signal phase changes in settings. Automatic frequency control circuit of the control voltage from the discriminator. We know that re-release and low frequency synchronization signal The existence of the same color signal frequency changes in the law of composition, re-release of the sync signal frequency discrimination can be reflected in changes in the frequency down-chroma components stern error voltage, this error voltage control circuit for automatic frequency control voltage,[link widoczny dla zalogowanych], superimposed on the automatic phase loop control voltage, automatic frequency control circuit is equivalent to the VCO control voltage to follow the reduced frequency of static frequency signal containing the amount of color change basking, to coarse role. The automatic phase control loop requires only small voltage control oscillator, the frequency of changes to make it component Li is consistent with low carrier frequency, therefore, of the scope of the phase locked greatly reduced.