JPS6042524Y2 - Frequency divider - Google Patents

Description

[Detailed Description of the Invention] The present invention utilizes the color subcarrier frequency (3,579545 MH2) of the NTSC standard color television signal and the color subcarrier frequency (4,4 MH2) of the PALi semi-color television signal.
33628MHz) are divided into 6
The present invention relates to a frequency dividing device that selectively extracts frequency-divided outputs closer to 0 Hz and 50 Hz.

The NTSC standard color television signal was developed as a compatible system for black-and-white and color receivers, and the 3.58 MH2 component is superimposed on the colored portions of color broadcasts on black-and-white receivers. , considerable interference is expected on the screen (hereinafter referred to as dot interference), but in order to reduce such interference, the NTSC
Color subcarrier frequency f of a standard television signal.

is selected to be a special value, always synchronized with the horizontal scanning frequency fH, and so that the frequency relationship is as follows.

fc = “X 455”” (1) On the other hand,
A low-frequency conversion VTR that converts the color signal of the above NTSC standard television signal to a lower frequency and records it on a magnetic tape.
, the color signal is stabilized at the frequency of the local carrier wave oscillator when the low band is converted back to the original band during playback, but the horizontal scanning frequency fH is determined by the magnetic tape transport speed deviation during playback or the servo system. Errors occur due to reference signal frequency deviation during playback, and the relationship in equation (1) above is no longer satisfied, resulting in dot interference on the screen of the television receiver, which causes a reduction in the image quality of the playback image. Ta.

The same can be said of the FAI system.

To explain this dot interference in detail, Figures 1 and 2 illustrate the relationship between the horizontal scanning frequency and continuous color subcarrier frequencies, and Figure 1 shows the frequency of the NTSC standard color television signal during recording. where A is the horizontal scanning signal, C is the continuous color subcarrier in the first scan, and C is the continuous color subcarrier in the second scan. The carrier waves are out of phase with each other by 180°, so if the scanning lines of the first and second scans are very close, the brightness and darkness caused by the peaks and valleys will cancel each other out on the screen of the television receiver. , dot interference caused by color signals is extremely reduced.

However, when the horizontal scanning frequency of the reproduced signal from the VTR changes, as shown in Figure 2, the color subcarriers on the screen of the television receiver are not canceled because their peaks and troughs are in phase as shown in (b) and (b).

Therefore, dot interference occurs on the screen of the television receiver, and in the case of the phase relationship shown in FIG. 2, it appears as a striped pattern of diagonal stripes.

The color subcarrier frequency f, with respect to the horizontal scanning frequency fH is l/
When interleaving with a two-offset relationship, dot interference is at a minimum and when in phase it is at a maximum.

Assuming that the first and second scans scan very closely on the television receiver screen, and let ψ be the phase difference between the continuous color subcarriers of the first and second scans, the dot interference on φ will be very close to each other. K.

Metrically, φ(t1φ) = T (stn2y−fct
(K is a visual correction value).

Rewriting d (t, φ), we get K.

d (t, ψ) = - (sm (2y, Jet) + s
in (2?rfat)cosφ +C08(2?rfot)Sinφ) =”-((Hcosφ) sin (2w+ct)+s
inφC03(2πfct)) =””! 1+cosφ) 2+5in2ψ・5i
n(2? rfot tentan-”1+.

. , J=-・,/2(1+cosφ) * sin (2?rfc t 1tan-"y=-
1cosrl *sin (2?rf, t+t...
...(2) Therefore, the dot interference amount D(φ) is d(t,
Since it can be expressed as the amplitude of φ), φ D(φ)=KICO8φ101 ・・・・・・(
3).

FIG. 3 is a graph showing the relationship of equation (3).

From Fig. 3, D(φ) becomes minimum when φ=π, 3π, -π, and φ=2W, 4w, o, -2? Maximum at r.

To convert φ into frequency, equation (1) can be rewritten as the following equation.

fo” (227+2) f )I
(4) From equation (4), the dot interference is at its maximum where the 172 offset disappears, so Δf corresponds to the following deviation.

227.5-227 ΔfH=X100=0.22 (%) ・・・・・・
(5) As a result of experiments on 227.5 dot interference, the permissible limit for the deviation of Δf)I is 0.1 to 0.15%, and the detection limit is 0.
．． A result of 0.05% was obtained.

The above-mentioned allowable limit value and detection limit value are determined by the frequency characteristics of the video circuit of the television receiver.

As explained above, in the capstan servo system during VTR reproduction, dot interference occurs due to the frequency accuracy of the reference signal of the servo system during reproduction, so it is necessary to improve this frequency accuracy.

The present invention uses this stable reference signal to generate a local subcarrier oscillator that is equal to the standard color subcarrier frequency used when inversely converting the low-pass conversion color signal built into the VTR, or to use the same frequency as the standard color subcarrier frequency used for color demodulation of the television receiver. This is a frequency dividing device used to obtain the output of the local subcarrier oscillator by dividing the frequency.
Examples thereof will be described below.

In Figure 4, the color subcarrier signal (3.5979545 MHz or P
In the AL, 4.433628MH2) is input, and is first divided by 1132 by the first frequency dividing circuit 2 consisting of a 7 frequency dividing circuit, and then divided by 2771 and 186 divided by an asynchronous counter. The signal is input to the frequency divider circuit 3 of No.2.

This second frequency dividing circuit 3 drives a switching circuit 6 by a control signal applied to an input terminal 7, and controls a pit decoding signal gate circuit 4 for 186 frequency division and a bit decoding decoding circuit 5 for 2771 frequency division. It is configured so that the output can be selectively switched and the frequency division ratio can be switched between 2771 frequency division and 186 frequency division.

In other words, for the signal input to input terminal 1, 597
Divide by 12 (NTSC (7)) Divide by 88672 (P
The selected frequency-divided output (at the time of AL) can be output to the output terminal 8.

Therefore, 3.579545MHz (NT
SC) is applied, the second frequency divider circuit 3 is
Operated as a 66 frequency divider circuit, 59.9468Hz
(0.011% deviation for 60Hz) output terminal 8
When 4.433628MHz (PAL) is applied, the second frequency divider circuit 3 is operated as a 2771 frequency divider circuit to output 50.0002Hz (0.0004% deviation from 50Hz) to the output terminal 8. These two output signals meet the dot interference detection limit of 0.
．． 05% can be satisfied even in the NTSC system and the PAL system.

As described above, the present invention divides the frequency of the color subcarrier signal and
Even in the NTSC and PAL systems, the frequency divider that creates the reference signal for performing phase synchronization control of the rotating body of R has a frequency division ratio that is below the dot interference detection limit of 0.05%. By setting the frequency dividing ratio, the operation of the frequency dividing circuit can be stabilized and the switching operation between NTSC and PAL can be performed after passing through the dividing station, so all you need to do is switch the reset gate signal using a simple asynchronous counter.
It is possible to switch between 66 frequency divisions, and NTS can be achieved with one series of frequency division circuits.
C/PAL can be shared.

Furthermore, by setting the frequency division ratio for NTSC to 59712 and the PAL division ratio to 88672, the influence of dot interference is also eliminated.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams showing the frequency relationship between the horizontal scanning frequency and the color subcarrier, Figure 3 is a diagram showing the calculated value of the amount of dot interference with respect to the phase difference of the color subcarrier, and Figure 4 is a diagram based on the present invention. FIG. 2 is a block diagram showing a frequency dividing circuit configuration. 1... Input terminal, 2... First frequency dividing circuit, 3... Second frequency dividing circuit, 4... Output terminal.

Claims (1)

[Scope of utility model registration request] A first frequency dividing circuit divides the subcarrier frequency of the NTSC standard color television signal or the subcarrier frequency of the PAL standard color television signal applied to the input terminal by 1132, and further divides the divided output by 2771. A frequency dividing device comprising a second frequency dividing circuit capable of selectively dividing the frequency into one frequency and one hundred and eighty-sixth frequency.