JPS62107590A - Phase distortion removal circuit - Google Patents

Abstract

PURPOSE:To eliminate color distortion by providing a high frequency crystal filter circuit, a low frequency crystal filter circuit, a circuit mixing output signals, the circuit doubling the frequency of a reference subcarrier, a phase detection circuit and a variable phase shifting circuit. CONSTITUTION:When among output signals from a band amplifier circuit 1, upper and lower side waves are applied to the crystal filters H1 L34 and the output signal is applied to the mixing circuit 5, signals at frequencies with the sum and difference between both signals can be taken out. The summed frequency component is amplified by an amplitude limit amplifier circuit 6, and applied to the phase detection circuit 9. On the other hand, a signal with a frequency twice that of the reference subcarrier is produced from the reference subcarrier generated by a reference subcarrier generator circuit 2, and a voltage corresponding to the phase difference between both signals applied to the phase detection circuit 9 controls the variable phase shifting circuit 7. Then the phase of the reference subcarrier is always operated by fitting a phase distortion angle.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color signal reproducing circuit for a color receiver, and in particular proposes a circuit configuration capable of removing phase distortion of a carrier color signal generated in a transmission path.

Currently, there are three color television systems used in countries around the world: the NTSC system, the PAL system, and the SECAM system, and each of these systems has its own advantages and disadvantages.

The biggest drawback of the NTSC system is that the phase and amplitude of the carrier color signal change in the micro repeater circuit, transmitter, and VTR, resulting in color distortion.On the other hand, the PAL system
Although this method improves on the drawbacks of the C method, it is inferior to the NTSC method in terms of compatibility, such as requiring a highly accurate one-line delay line and lowering the vertical color resolution.

The present invention aims to make the NTSC system the most advanced system by solving the problem of color distortion, which is the biggest drawback of the NTSC system, and will be described in detail below.

In the NTSC system, a luminance signal EY and two color signals I, E, and Q signals are created from the primary color signal ER+ EG r EB. ■ The signal and Q signal each modulate the subcarrier with two balanced modulation circuits. Two subcarriers with the same frequency but a 90' difference in phase are used for modulation. This carrier color signal is superimposed on the luminance signal and sent as a composite color television signal, and the subcarrier serves as a reference when color demodulation is performed in a receiver. is required, so 8 to 10 cycles of a color printing carrier wave are inserted at the trailing edge of the horizontal synchronization signal and sent.

The I signal E, , Q signal E0, and carrier color signal EC of the NTSC system are as follows.

E+=-0,27(Ea EY)+0.74(ER
-Ey) Tl1EQ = 0.42 (Ea-
Ey) +0.48 (EREY) (21Ec
”= EI cos (ω5t-4-33°) ten EQ
sin (678t +33°) (3) Generally, color receivers receive and process color difference signals, so assuming that ER-EY and EB-EY times the signals are being sent, the carrier color signal is as follows.

Figure 1(a) shows the vector of the carrier color signal.If the amplitude of the carrier color signal is the angle measured counterclockwise with the phase of EB-EY being 0°, then the ζ method is as follows. EC-αsin
φcosωst +αC, 09φsinωs t f51 The frequency distribution of the color television signal superimposed with the carrier color signal is
2) As shown in the figure, the carrier color signal component is inserted between the luminance signal components distributed at intervals of the horizontal scanning frequency.

In the case where the color signal is a sine wave signal, the two-sided waves, which are n times the horizontal scanning frequency above and below the subcarrier, are α' =
If Dsinpt, (where p=2nπfh, fh
is the horizontal scanning frequency) From equation (5), EC = Dsinφ・5inpt+CO9ωst+Dc
osφ+5inpt −sinωs t (6
1, and rearranging this, EC= D/2 ・cos ((ωs −p) t−
φ)−D/2・cos((ωs+p) tenφ)
(The lower side wave and the second side wave of the force carrier color signal are at an angle θ
When subjected to a phase distortion of , the carrier color signal becomes as follows.

Ec' = D/2 ・cos ((ωs −p)
-φ-θ)-D/2・cos((ωs+p) is 1φ
-θ) (8) The part surrounded by dotted lines in the circuit diagram of FIG. 3 shows one embodiment of the present invention, and its function will be explained below.

The upper side wave D/2・c of the output signal of the band amplifier circuit f+1
os((ωs+p)t+φ−θ) is added to the crystal filter circuit H(3), and the lower side wave D/2・cos((ψ5−
p) Add t-φ-01 to 4) using a crystal filter,
The crystal oscillator used in the crystal filter circuit H (3) resonates at a frequency that is n times higher than the vertical scanning frequency than the subcarrier frequency, and the crystal oscillator used in the crystal filter circuit L (4) resonates at a frequency that is n times higher than the subcarrier frequency. It resonates at a frequency n times lower than the vertical scanning frequency.

When the signals that have passed through these two crystal filter circuits are added to the mixing circuit (5), signals with the sum and difference frequencies of both signals are extracted.Actually, a balanced modulator is used in the mixing circuit. The component cos2 (ω8 is - θ) is amplified by the amplitude limiting amplifier circuit (6) and applied to the phase detection circuit (9).

On the other hand, the reference TA generated by the reference subcarrier generation circuit (2)
The 11 carrier waves are passed through a variable phase shift circuit (7), and a frequency doubling circuit (8) generates a signal variation cos2ωst with a frequency twice that of the reference subcarrier, which is then passed through a phase detection circuit (9).
This voltage is added to the phase detection circuit (9) to generate a voltage according to the phase difference between the two signals. This voltage controls the variable phase shift circuit (7) and changes the phase of the reference subcarrier. It always operates to match the phase distortion angle.

Next, the removal of phase distortion will be explained with reference to FIG.
Demodulating on the Y axis naturally causes color distortion, but R-Y
By changing the phase of the demodulation axis of %BY by θ, phase distortion can be completely removed.

As explained above, the effect of the present invention is to solve the problem of color distortion, which is the biggest drawback of the NTSC system. Furthermore, in the PAL method, saturation distortion increases as the phase error increases, but this invention does not have this, and the effect of removing color distortion is perfect.

In the example, a case will be explained in which a phase comparison is made between the frequency component of the sum of the signals passing through two crystal filter circuits and the frequency component twice the reference subcarrier. Even if the frequency component of the sum of the signals passing through the circuit is divided by two and the phase is compared with the reference subcarrier, the effect is the same and can be easily considered.

[Brief explanation of drawings]

FIG. 1(a), +1)) is a vector diagram of a carrier color signal. Figure 2 is an energy distribution diagram of a color television signal. FIG. 3 is a circuit configuration diagram of the present invention. What about (1)? iF range amplifier circuit. (2) is a reference subcarrier generation circuit. (3) is a crystal filter circuit H0 (41 is a crystal filter circuit ■). (5) is a mixing circuit. (6) is an amplitude limiting amplifier circuit. (7) is a variable phase circuit. (8) is a frequency doubling circuit. (9)
is a phase detection circuit. Patent applicant Michitaka Haruno Figure 1 (ω) (b) Kei 2 Figure Hand 3rd ward

Claims (1)

[Claims] In the color signal reproducing circuit of a color receiver, a crystal filter circuit H(3) has a frequency higher than the subcarrier frequency by an integral multiple of the horizontal scanning frequency, and a crystal filter circuit L has a frequency lower by an integral multiple of the horizontal scanning frequency. (4), a circuit (5) that mixes these output signals, a circuit (8) that doubles the frequency of the reference subcarrier, a phase detection circuit (9), and a variable phase shift circuit (7). phase distortion removal circuit.