JPS6247396B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reference signal forming circuit used in a beam index type color receiver.

In a beam index type color picture tube, a single electron beam scans a phosphor surface on which red, green, and blue color phosphor stripes are arranged repeatedly in the horizontal scanning direction. Index phosphor stripes are arranged on the inner surface in the horizontal scanning direction, and an index signal obtained by scanning the index phosphor stripes with an electron beam causes the electron beam to scan the red color phosphor stripes. When scanning, the red primary color signal is used,
When scanning a green phosphor stripe, a green primary color signal is used, and when a blue phosphor stripe is scanned, a blue primary color signal is used for density modulation.

In order to selectively supply primary color signals according to the scanning position of the electron beam, a gate signal for the primary color signal is required, but the reference signal for obtaining this gate signal is formed as shown in Figure 1. It can be obtained by a circuit. However, in this example,
The pitch of the index phosphor stripe is red,
This is the case using a color picture tube in which the pitches of the green and blue color phosphor stripes are chosen to be equal (generally an integer multiple).

In the figure, 1 is an index type color picture tube, and a lens 2 is attached to a part of its funnel to receive the light emitted when the electron beam scans the index phosphor stripe.
A photoelectric converter 3 is disposed outside the photoelectric converter 3 to detect an output corresponding to the arrangement of the index phosphor stripes. And this output is passed through band pass filter 4
A signal of the fundamental period of the index phosphor stripe, that is, an index signal S _I is extracted.

Further, the primary color signals E _R , E _G , E _B supplied to the terminals 6R, 6G, 6B are supplied to the gate circuits 7R, 7G, 7
It is supplied to the color picture tube 1 through B. Reference numeral 10 denotes a circuit for forming gate signals P _R , P _G , and P _B , and the gate signals P _R to P _B formed based on a reference signal So described later are arrays of colored phosphor stripes corresponding to red to blue, respectively. These are pulse signals whose period is pitch, and there is a predetermined phase difference between them. and,
The phases of these gate signals P _R to P _B are regulated by the index signal S _I.

20 is a circuit for forming the reference signal So, where the reference frequency _p is n times the index frequency _i (where n is an integer), and m of the frequency _g of the gate signals P _R to P _B.
(where m is an integer) is selected. Forming circuit 20
is configured as a PLL, and 21 is a VCO.
The reference signal So, which is the output of VCO21, is output from counter 2.
2 is counted down to I/n, and its output is supplied to the phase comparator 23 together with the index signal S _I , and the phases of the two are compared. Since the index signal S _I includes a gate timing error component (phase error) Δ, this phase error Δ
A comparison output EΔ corresponding to is obtained, which is supplied to the VCO 21 as a control voltage through the low-pass filter 24.

By the way, the signal frequency supplied to the phase comparator 23 is _i (= _p /n), so the cutoff frequency _c of the low-pass filter 24 is at most 2 _i
The response speed of the PLL is determined by this signal frequency. The faster the response speed of the PLL, the faster the correction speed for gate timing deviations, so it is desirable to make this response speed as fast as possible.

Therefore, the present invention is designed to improve the response speed compared to the conventional technology with a relatively simple configuration. Therefore, in this invention, the signal frequency supplied to the phase comparator 23 is increased.
As shown in _FIG .
The frequency _p is counted down to 1/n,
This output is sent to the first mixer 27 along with the reference signal S _p
The frequency is mixed. This mixed output S
_M1 is further supplied together with the index signal S _I to a second mixer 28 for frequency mixing. The mixed output S _M2 is then supplied to the bandpass filter 29, and in this example, the mixed output equal to the reference frequency _p , that is, the comparison output S _Mp , is extracted and separated.

Here, if the reference signal So of the VCO 21 is set as So=cos(2π _p t)...(1) and the index signal S _I is set as S _I =cos(2π _i t+Δ)...(2), the first mixture Since the output S _M1 is S _M1 = cos {2π ( _p ± _p /n) t} (3), if this first mixed output S _M1 and the index signal S _I are further frequency-mixed, the second
_{The mixed output SM2 of _ _}
By passing it through, a comparison signal S _Mp having a frequency of _p and a phase error Δ is obtained, as shown in S _Mp = cos (2π _p t + Δ) (5).

Therefore, by comparing the phases of this comparison signal S _Mp and the reference signal So, it is possible to obtain a control voltage according to the phase error Δ, as in the conventional case. At this time, the cutoff frequency _c of the low-pass filter 24 is maximum 2
You can choose up to _p , that is, 2n _i . By increasing the frequency of the signal input to the phase comparator 23 in this manner, the response speed of the PLL becomes much faster than in the past.

It is also possible to form the comparison signal S _Mp with frequency _p and phase error Δ using a frequency multiplier circuit without using the mixer described above, but in this case, the phase error would also be multiplied. undesirable.

As explained above, according to the present invention, the signal frequency to be phase-compared can be made n times higher than that of the conventional method, which has the effect of increasing the response speed of the PLL accordingly.

It should be noted that the invention can also be applied to color picture tubes in which the pitch of the index phosphor stripes is not selected to be an integral multiple of the pitch of a set of color phosphor stripes.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a reference signal forming circuit for a beam index type color receiver used to explain the present invention, and FIG. 2 is a system diagram of a reference signal forming circuit showing an example of the present invention. 1 is a color picture tube, 10 is a gate signal, P _R ~
20 is _a formation circuit for the reference signal So,
21 is a VCO, 27 and 28 are mixers, 23 is a phase comparator, and 24 is a low-pass filter.

Claims (1)

[Claims] 1. A reference signal forming circuit provided to form a gate signal for gating the primary color signals supplied to the beam index color picture tube.
The reference frequency of the VCO composed of a PLL and provided in the reference signal forming circuit is set to n times (n is an integer) the frequency of the index signal detected from the color picture tube, and the output signal of the VCO and the above
A signal obtained by dividing the output signal of the VCO by n is mixed by a first mixer, the output signal of the first mixer and the index signal are mixed by a second mixer, and the band bus is mixed by the second mixer. Obtain a comparison signal through a filter, compare the phase of the comparison signal with the output signal of the above VCO, and use the comparison output to
A reference signal forming circuit for a beam index color receiver that controls the oscillation frequency of the VCO.