JPH03267894A - Luminance and color difference signal separation circuit for color television signal - Google Patents

Abstract

PURPOSE:To avoid the accumulation of a phase error by adding a prescribed phase difference sequentially between sampling points to an initial phase, obtaining a phase of a subcarrier at each sample point and converting the phase into an amplitude of a sinusoidal wave signal and a cosine signal. CONSTITUTION:An initial phase calculation section 71 calculates an initial phase theta of an initial sample signal based on an initial amplitude ratio corresponding to an initial phase from an initial value calculation section obtained by sampling two points of the middle part of a color burst of a chrominance carrier signal, an initial amplitude and the polarity of sin-cos transformation value, and a phase generating section 72 adds sequentially a prescribed phase difference phito the initial phase theta to generate a phase of a subcarrier at each sampling point. Then a phase-amplitude conversion memory section 73 converts a phase of each sample point of the color burst into an amplitude of a cosine and sine wave signal of the subcarrier. Thus, the accumulation of the phase error by multiplication of sin and cos values is avoided.

Description

[Detailed Description of the Invention] (Summary) Regarding a luminance signal and color difference signal separation circuit for data digitized with a sampling clock that is not an integer multiple of the subcarrier of a color television signal, the phase difference s of each sample point is
The purpose is to obtain the in value and cos value without multiplying them, and the sine-cos generation unit calculates the initial value of the sample signal from the initial amplitude ratio corresponding to the initial phase, the initial amplitude, and the polarity of the sine-cos converted value. an initial phase calculation unit that calculates the phase; a phase generation unit that generates the phase of a subcarrier by sequentially adding a predetermined phase difference between each sample point to the initial phase; and a phase-amplitude conversion memory unit that converts the amplitude of the wave signal.

[Industrial application field]

The present invention relates to a luminance signal and color difference signal separation circuit for color television signals, and more particularly to a luminance signal and color difference signal separation circuit for data digitized with a sampling clock that is not an integral multiple of the subcarrier of a color television signal.

In order to reproduce a color TV signal, it has been common practice to separate the luminance signal and color difference signal from the analog color TV signal, but this requires complicated circuitry and problems with separation accuracy and stability. The degree is not good either.

Therefore, there is a demand for digitization of color television signals, and as shown in CCIRRec no.
In order to be able to commonly support both 50 frame PAL signal formats, 13 frames are used as the sampling clock.
．． 5 MHz is recommended, and the frequency of 13°5 MHz is required not to be an integer multiple of the subcarriers of the color television signal.

[Prior Art] Figure 4 shows an example of the configuration of a conventional luminance/chrominance signal separation circuit for color television signals (Japanese Patent Application No. 63133997 filed by the present applicant).
(No.).

In the figure, l is a clamp circuit, 2 is a phase controlled oscillator (hereinafter P
LO), 3 is an A/D converter, 4 is a delay section, 5 is a comb filter, 6 is an initial value calculation section, 7 is a sin-co
s starting section, 8 is a first multiplier, 9 is a second multiplier, and 10 is a first LPF (low pass filter), 11
is the second LPF, and 12 is the third LPF.

The analog NTSC signal a is clamped by a clamp circuit 1 and the DC component is regenerated, and at the same time, a horizontal synchronization color difference signal of the NTSC signal is detected and a horizontal synchronization pulse b is output.

Horizontal synchronization pulse b is PLO of frequency 13.5M) I2
2 and synchronized with the horizontal synchronization signal.
Generate a clock C that is not an integer multiple of the subcarrier with a frequency of z. This clock C is input to the A/D converter 3, which operates as a sampling clock for the NTSC signal output from the clamp circuit 1, outputs a signal d obtained by digitizing the NTSC signal, and samples the operation of each part of this circuit. It becomes a clock (not shown).

NT which is the output d of the digitized A/D converter 3
The SC signal is delayed for a certain period of time by a delay unit 4 and sent to a comb filter 6, which outputs a carrier color difference signal together with a luminance signal.

The luminance signal g passes through the first LPFIO and becomes a signal Y signal component (luminance signal) m, and the carrier color difference signal is (B-Y) sin ωt + (RY) cos ωt
This will be shown as

Next, in order to obtain a color difference signal from the carrier color difference signal from the comb filter 5, an initial value calculation section 6 and a sincos generation section 7 are provided, and the signal is multiplied by the output of the comb filter 5, respectively.

That is, the sin-cos generator 7 generates a sin ωt component signal 1 phase-synchronized with the color burst, and this sin ωt component signal 1
CO3ω shifted by 90 degrees from the component signal i of t is the component signal j
Outputs (B-'y') sin ωt + (RY) cos
The carrier color difference signal represented by ωt is multiplied by the first multiplier 8 and the second multiplier 9 to obtain the signal.

Note that the components of sin ωt and CO5ωt are, first, A
After the initial value calculation section 6 calculates the output S1 and the output CI, which are initial value outputs, from the color burst in the output of the /D converter 3, the sin-cos generation section generates the output S1 and the output CI.

Further, the delay of the delay circuit 4 functions to delay the NTSC signal d signal by the calculation time of the initial value calculation section 6.

FIG. 5 shows an example of the configuration of the above-mentioned initial value calculation unit 6, in which the DC component of the pedestal component is removed from the digitized NTSC signal d-signal burst by the BPF 51, and the color burst detector 52, as shown in FIG. 6, the amplitudes S1 and 52 of two consecutive sample points in the central part of the color burst are extracted.

These two sample point amplitudes 51. The initial value is determined based on S2, but first the maximum amplitude A of the color burst is determined.

That is, in FIG. 6, sample signals S1. Each amplitude of S2 can be expressed as follows.

51 = Asinθ 52 = Asin (θ+φ) = Asinθcosφ+Acosθsinφ=Slco
sφ+Acosθsinφ(+)where, θ indicates the phase of an arbitrary sample point S1 in the central portion of the color burst, and φ indicates the phase of one sample from the sample point S2.

Transforming equation (1) and squaring both sides, we get (52-5lc
osφ)”=A”cos”θsin”φ. Here, since A"costθ+A"sin"θ-A2, from A"cos"θ÷31", A", (S2-5lcosφ)"=A"cos"θsin"φ
=(A"-51") sin"φ. Therefore, the maximum amplitude A is as follows.

This is the first adder 53a, ×cos
A value calculated by the φ calculator 54, the XI/sin φ calculator 55, the first squarer 56a, the second squarer 56b, the second adder 53b, and the square root calculator 57, This is the output of the square root calculator 57.

Next, the number of outputs of the square root calculator 57 ([based on A,
The maximum number that can be expressed in bits of output is 128/
The x operator 58 (applies A to X) and the multiplier 59
By determining l/A, a normalized value S1° is determined when the maximum amplitude A is 1, and the sin-cos converter 60
The CI is determined from |S1'. Furthermore, this operation is
This is done every time a color burst is input for each line.

FIG. 7 shows an example of the configuration of the sin-cos generation generating section, and the first selector 71 and the second selector 72 are circuits for selecting input signals, and the initial value S1 and the initial value C
Until 1 is determined by the initial value calculation unit 6, the S1 and C1 sides are selected.

Then, Sl and 01 are found, and the first register 73 and the second
Once stored in the register 74, the opposite output side is selected and one line of sine value and cosine value data is sequentially output using the following recurrence formula.

That is, the nth sine value S1 and cosine value C5 are calculated using the n1th data, S,=S,l-1cosφ+CI1. sinφCl1−
It is calculated by C11-1cO5φ-5ll-+sinφ.

In addition, 75 to 7 days are the first to fourth multipliers that multiply the constants sin φ and cos φ, and 79 and 80 are the first adder and second adder, which multiply the constants sin φ and cos φ. Ingredients and co
Find the component of sωt.

The signal shown in FIG. 4 is obtained by multiplying the thus obtained sin ω component, the cos ω L acid component, and the carrier color difference signal by the first multiplier 8 and the second multiplier 9. Since the second harmonic component is included in the 100 output of Component (color difference signal) n, and R-
Both color difference signals with the Y signal component (color difference signal) being 0 are output.

[Problem that the invention sought to solve]

In such a conventional circuit, the sine-cos generation unit 7 generates the sine wave cos of the subcarrier at each sample point.
To obtain the wave, the sine value of the phase difference φ of each sample point,
Since the cos values are multiplied and added, there is a problem in that calculation errors due to multiplication accumulate, and the phase error gradually increases after initial setting.

Therefore, in the present invention, as shown in FIGS. 4 to 7, a color television signal digitized with a sampling clock that is not an integer multiple of the subcarrier is delayed for a certain period of time in a delay section, and then processed by a comb filter. Separate into a luminance signal and a carrier color difference signal, detect a color burst from the digital signal, and extract the signal at two consecutive sample points in the center of the color burst to find the maximum amplitude of the sample signal and extract the initial sample. An initial amplitude ratio corresponding to the initial phase with the amplitude of the signal is determined by an initial value calculation section, and from the initial amplitude ratio, a sine wave signal and a cosine wave signal for one line whose phase is synchronized with the color burst are generated by a sine-cos generation section. , the sine wave signal is multiplied by the carrier color difference signal in a first multiplier, the cosine wave signal is multiplied by the second multiplier, and the luminance signal is multiplied by the first multiplier. In a luminance/chrominance separation circuit for a color television signal, which band-limits the output of the output and the output of the second multiplier using a low-pass filter to obtain a luminance signal and two chrominance signals, the sine value of the phase difference of each sample point,
The purpose was to obtain the cos value without multiplying it.

[Means to solve the problem]

FIG. 1 shows the principle of the configuration of a luminance/color difference separation circuit for color television signals according to the present invention.
The in-cos generation unit 7 generates an initial amplitude ratio l517A1 corresponding to the initial phase of the initial sample signal and an initial amplitude |S1
and an initial phase calculation unit 71 that calculates the initial phase of the initial sample signal from the polarity of the sin-cos conversion value C1;
a phase generator 72 that generates a subcarrier phase by sequentially adding a predetermined phase difference between each sample point to the initial phase; and a phase generator 72 that converts the subcarrier phase into the amplitude of the sine wave signal and cosine wave signal. and an amplitude conversion memory section 73.

Further, in the present invention, the above predetermined phase difference is (455/L
)~, and it is preferable to select the period N of the subcarrier and the number of samples of the two lines so that the predetermined phase difference is a natural number.

[Function] In the present invention, the initial amplitude ratio I Sl/A corresponding to the initial phase from the initial value calculation unit 6 obtained by sampling the central portion of the color burst of the carrier color difference signal at two points, and the initial amplitude S
1 and its sin-cos conversion value C1 (corresponding to |S1' CI in FIG. 5), the initial phase calculation unit 71 calculates the initial phase θ of the initial sample signal, and the phase generation unit 7
In step 2, a predetermined phase difference φ is sequentially added to this initial phase θ to generate the subcarrier phase at each sample point.

Then, the phase-amplitude conversion memory unit 73 converts the amplitudes of subcarrier sine wave signals and cosine wave signals corresponding to the phase of each sample point of the color burst.

This avoids accumulation of phase errors due to multiplication of sine and cosine values.

However, if the above predetermined phase difference φ itself contains an error,
Since the cumulative error due to sequential addition (which is much smaller than the cumulative error due to multiplication) occurs, the period N of the subcarriers and the number of samples on the 2 lines are calculated as (455
/L) If L and N are selected so that the predetermined phase difference φ represented by N is a natural number, the error in the phase difference φ itself disappears and the cumulative error can be removed.

〔Example〕

FIG. 2 shows an embodiment of the sine-cos generation part of the luminance/color difference separation circuit for color television signals according to the present invention shown in FIG. 1, and the other configuration is the same as the conventional one. The configurations shown in FIGS. 4 and 5 may be used.

In the embodiment shown in FIG. 2, the initial phase calculation unit 71 calculates the maximum amplitude A of the color burst obtained as shown in FIG. Initial amplitude ratio S corresponding to the initial phase with the initial amplitude S1
The initial phase θ is calculated from l/A as θ=sin-'(l Sl/
A I ) (Sl, CI >0)・18
0'-sin-'(l Sl/^1) (Sl>0
．． C1<O)・360'-sin-'(l Sl/A
I) (Sl<0, C1>O)=270
°−sin−′(l Sl/A I ) (|S1<
0, CI<O).

Although the initial value S1° in the conventional example shown in FIG. 5 is normalized, it is actually the initial amplitude ratio 51/A
is equivalent to

In addition, in the phase generation section 72, a selector 72a that selects the output of the initial phase calculation section 71 for the first one sample, and then selects the other input, and a phase difference φ of each sample point in the output of this selector 72a. and a register 72c that temporarily holds the output θ+φ of the adder 72b and provides the output to the other input of the selector 72a.

Here, the phase difference φ is φ・(455/L)N It is expressed as

That is, as shown in FIG. 3(a), two lines of the NTSC system are composed of L pixels (number of samples), and 455 subcarriers are included in these two lines. Since the sample point S1.52 is only 1 sample apart, the phase difference due to 1 sample is equal to 1 period of the subcarrier by L/4
If it is set to 55, it becomes 1 (same figure [available])).

In other words, since the following relationship holds true: 1:L/455=φ:N (N is the period of the subcarrier), it becomes φ·455/L×N.

In this case, by selecting the period "N" of the subcarrier and the number of samples "LJ" for the two lines so that the phase difference "φ" is a natural number, it is possible to eliminate the accumulation due to the addition of phase errors. Become.

For example, if L=1716, φ=455/1716
X N becomes φ, φ−in and N+ where N is a natural number
*in is φ■in・455, Nm1n= 1716
becomes.

This is 1 if one period N of the subcarrier is expressed as 1716.
The sample number shows that 2 kore is 455 (
Figure 3 (C)).

In addition, in this case, the initial phase θ at the sample point S1 is 1-1716 because it is somewhere within one period of the subcarrier.
Takes one of the values.

That is, θ has an error of 360/1716=0.21' because it is rounded off to a point that divides one period of 360° into 1716 equal parts.

In FIG. 3(b), if the phase of point S1 is θ·50′, it becomes Sl·1716/360×50#238.

At this time, the points after 32 are sequentially separated by φ, so 52
=31+φ=238+455=693 (145°)S
3=S2+φ・693+455・1148(241'
)S4・S3+φ=1148+455=1603(33
6”)S5・S4+φ・1603+455・2058
(432°).

However, only the error due to the rounding as described above remains, and even if the addition unit 72b adds as described above, the errors will not be accumulated.

Here, the value 2058 of the fifth sample point S5 is 171 for one period.
6, 2058-1716 = 342 (72
°).

In this way, the selector 71a selects the initial phase θ only at the beginning, but after that, the predetermined phase difference φ is sequentially added to the ROM 73 as a phase-amplitude conversion memory.
Data is stored in advance so as to generate a sine wave and a cosine wave by giving the amplitude values of each sample point in the sine curve of FIG.

〔Effect of the invention〕

As explained above, in the present invention, a phase corresponding to a sample point in a color burst is calculated as an initial phase, and a predetermined phase difference between each sample point is sequentially added to the initial phase to calculate a subcarrier at each sample point. Since the phase of the subcarrier is generated and the phase of this subcarrier is converted into the amplitude of the sine wave signal and the cosine wave signal by the memory, it is possible to eliminate the multiplication using the sine wave signal and the cosine wave signal. By doing this, it is possible to create sine wave signals and cosine wave signals synchronized with subcarriers that avoid accumulation of phase errors due to multiplication.

In addition, in the present invention, if L and N are selected such that the predetermined phase difference φ represented by (455/L) N is a natural number due to the period N of the subcarrier and the number of samples of 2 lines, the phase difference φ The error itself is eliminated, and the cumulative error due to addition can also be eliminated.

73... Phase-amplitude conversion memory section, θ...Initial phase, φ...Predetermined phase between samples.

In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (2)

[Claims] (1) A delay unit (4
), the signal is separated into a luminance signal and a carrier color difference signal by a comb filter (5), a color burst is detected from the digital signal, and two consecutive sample points in the center of the color burst are detected. The maximum amplitude (A) of the sample signal is obtained by extracting the signal, and the initial amplitude ratio (|S1/A|) corresponding to the initial phase with the amplitude (S1) of the initial sample signal is determined by the initial value calculation unit (6). ), and from the initial amplitude ratio (|S1/A|), one line of sine wave signal and cosine wave signal phase synchronized with the color burst are sin
A first multiplier (8) multiplies the sine wave signal by the carrier color difference signal, and a second multiplier (9) multiplies the cosine signal by the cosine signal. ), and the luminance signal, the output of the first multiplier (8), and the output of the second multiplier (9) are passed through low-pass filters (10), (11), and (12), respectively.
In the luminance/chrominance separation circuit for a color television signal which obtains a luminance signal and two color difference signals by band-limiting, the sin-cos generating section (7) calculates the amplitude ratio (|S1/
A|), the initial amplitude (S1), and the polarity of the sin-cos conversion value (C1) of the initial phase calculation unit (71) that calculates the initial phase of the sample signal; A phase generation unit (72) that generates the phase of a subcarrier by sequentially adding constant phase differences; and a phase-amplitude conversion memory unit (73) that converts the phase of the subcarrier into the amplitude of the sine wave signal and the cosine wave signal. A brightness/color difference separation circuit for color television signals, characterized by comprising: (2) The predetermined phase difference is expressed as (455/L)N, and the period N of the subcarrier and the number of samples L for two lines are selected such that the predetermined phase difference is a natural number. 2. The luminance/color difference separation circuit for color television signals according to claim 1.