JPH01152893A - Method generating color signal in secam system by digital processing - Google Patents

Abstract

PURPOSE:To generate a highly stable chrominance signal with simplified structure by storing Y, R-Y, B-Y signals into a memory as a digital value subject to pre-emphasis, applying digital FM conversion and sinusoidal wave conversion to the R-Y, B-Y signals, adding the Y signal and applying D/A conversion so as to extract the chrominance signal. CONSTITUTION:A ROM 4 is a DR memory in which a data subject to pre- emphasis in 12 or 10 bits is stored. A data selector 8 uses a discrimination signal so as to switch DR, DB to match the time of FM conversion and sinusoidal conversion. A converter 10 converts the DR or DB waveform outputted from the data selector 8 into FM wave 16-bit data and into a sinusoidal wave by the ROM. An adder 14 adds a chrominance data and the Y signal to form a video signal. Then a D/A converter 15 applies D/A conversion to the digital output of the adder 14 to convert it into an analog signal. Thus, the adjustment of pre-emphasis, limiter, frequency and level filter is not required and since the stability depends only on the reference clock, high stability is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a method of creating a television color signal using the SECAM system.

(Prior art and its problems) Conventionally, television color signals based on the SECAM system are usually created by analog signal processing. For this reason, the apparatus has the disadvantage of being large in size, requires adjustment at each processing stage, and, moreover, it is difficult to obtain a signal with high frequency stability.

(Object of the Invention) The present invention digitizes conventional analog processing to simplify the structure and create color signals using the SECAM method, which can create highly stable color signals without adjustment. This provides a method to do so.

(Structure and operation of the invention) The present invention will be explained in detail below with reference to the drawings.

The features of the SECAM system, which is the object of the present invention, are as follows.

■ FM conversion of chroma components ■ Level correction by FM wave filtering (bell filter) ■ Pre-emphasis ■ Separation of DR and DB axes, alternate transmission If the sampling frequency is locked to the horizontal period), it is possible to transmit the data.
This is not often done because it is difficult to create waveforms.

Therefore, the present invention proposes a digital generator that relies on hardware mainly for FM, which is a problem when producing waveforms. Below are the above items ■, ■, ■.

Explain according to ■.

(2) FM conversion of chroma components When respective determined levels are given to R-Y and B-Y, a single frequency is specified.

Figures 1(a) and 1(b) show the bell filter characteristics, the DR axis,
Although the center values indicating the respective waveforms at the respective center values of the DB axis are shifted, the frequencies specified by the given levels (positions) are constant for both DR and DB. Therefore, if a level is given, a signal of that frequency can be generated.

FIG. 2 shows the circuit of the FM converter based on level values. D.R.
, DB are input as 12-bit data, and the offset data is a numerical value representing the minimum frequency in the SECAM chroma system. 21 and 2
2 is added by adder QA21, resulting in 16-bit data 23. If the initial value of 24 is "0", then the output of adder QA12 will be 25=23. Here, when the clock arrives, the current numerical value is held by the latch QA23. The held data becomes 26 and 24 and is output. Then, the value of 25 is the output 26, the current R-Y/B-Y data 21, and the offset data 2.
The value is the sum of 2. From the next clock, it is held as the output 26, and from then on, as the clock is input, the output 26 shows the value obtained by continuing to add the numerical values of the inputs 21 and 22.

As this process is repeated, if the value exceeds the value that can be expressed in 16 bits, the output will show a smaller value, but the same addition will continue, resulting in a numerical value output as shown in Figure 3. The horizontal axis is the time axis, and the vertical axis shows the accumulated values, d
is the offset value plus DR/DB data.

The relationship between the numerical value produced by the adder as shown in FIG. 4 and the frequency is shown below. 0 to 6555 phase change from 0 to 360°
36 (16-bit data), and the sampling clock fsr is 17.625 MHz. If data M is set within the IH section, M will be added 1128 times. Furthermore, 16
If the number of cycles is calculated in bitwise order (one cycle per carry of 65536), then the frequency when data M is set is as follows.

On the other hand, it is tonal due to f3p=1128f□. Yacht, SECAM, DRvi transmission is frs
+=282fH, and DB subcarrier fvll=272fH.

Moreover, if M changes continuously at this time, the frequency will change in proportion to M.

From equation (1), the lower limit of the chroma frequency of SECAM is 3.7.
When it is 36000MHz, fHo=3.736000MHz fsp=17.
625M) lzM = 13891.7', 1389
The error when 213891.7 is set to 13892 is 3.
736061MIIz is enough because the error is 61Hz.

Also, the upper limit of SECAM chroma frequency is 4.836MH
z, the difference between the upper and lower limits of sP is 17982 to 13892 = 409
It is 0. If you change it from 0 to 4090, S
This means that it can fully handle everything from the maximum value to the minimum value of ECAM.

The phase amount in sawtooth wave performance can be shaped by driving a ROM in which a sine waveform is written using the sawtooth wave value as an address. FIG. 5 shows the relationship. D R/B
When the two values of the input data of R intersect, the speed at which the sawtooth wave is heliset (carry overflow) changes, and the frequency can be changed as shown in FIG.

■ Digital Bell Filter A bell filter is a type of BPF. Given any frequency, the level is returned as a single number.

If the R and DB data are entered as shown in FIG. 1, the amount of attenuation will be determined by the respective values of DR and DB.

Depending on the value of M that is set, it is sufficient to have the attenuation amount according to the equation as ROM data.

In the case of SECAM chroma, the frequency is determined by the DR and DB, so the frequency can be controlled by feeding back the DR and DB. Therefore, strictly speaking, it includes an offset rather than accurate R and DB.

FIG. 7 shows an example of a bell filter.
The figure is a characteristic diagram. Here, 71 is the level value of DR/DB. The ROM of QA71 contains the Bell constant. This ROM performs data conversion and maintains a certain level of F.
It can be multiplied by the MM7C3 multiplier QA72 to produce an FM wave with a bell filter. Multiplier QA
72 creates 24-bit data, but the lower 12 bits are cut off* 4095/4095 = 4095
becomes. This allows the level to be reduced.

■ Pre-emphasis This is a type of filtering that emphasizes the contours of DR and DB.

According to f I = 85 (Kllz), DR',
DB' data has been emphasized to ROM or RAM.
write to. Figure 9 (
A digital emphasis filter will be applied using the steps shown in a) (b) and (C).

In this state, when the signal is passed through the FM converting circuit (2) and the bell filter (2), a chroma component can be created by the procedure shown in FIG. Note that, as shown in (2), a gate is applied with 5CBL to remove the chroma component in the BL period.

■Separate and alternate transmission of DR and DB axes This is done by adding DR/DB discrimination signals (PAL, P) in the V-axis line memory (12 field memory) and switching for each IH. Also, the phase of the FM wave (0”/1
80'') and inverting the bit at the time of the sawtooth wave can switch the phase.

An example of the block configuration of an actual SECAM digital generator is shown in FIG.

The crystal oscillator 1 is a generator with a sampling frequency of CLK generation blank digital data synchronized with fH, and in this case, 17.625 Mtlz is used.

A synchronization signal generator 2 generates various synchronization signals such as 5YNC, HD, VD, PALP, and BF necessary for SECAM synchronization from the oscillator 1.

The counter 3 generates an address obtained by dividing the horizontal period by the clock CLK. The ROM 4 is a DR memory, and contains 12-bit or 10-bit pre-emphasized data.

ROM5 is a DB memory, and the contents are the same as ROM5. Counter 6 is a counter for 12 fields, and fH
are counted sequentially to create an address bus.

From the address created by the counter 6, the V-ROM 7
The memory contents of 12 fields are output and rows (ROM) are switched according to external pattern selection.

Data selector 8 is DR, D by PAL, P.
This is done by switching B to adjust the time for FM exchange and Sine conversion.

The delay circuit 9 adjusts the time for FM exchange and Sine conversion in order to input the original data to the digital bell filter.

The converter 10 converts the DR or DB waveform outputted by the data selector 8 into FM wave 16-bit data, and converts it into 16-bit FM wave data.
M makes it a sine wave (12 bits).

5CBL deletes unnecessary clocks, and BF' switches between Oo and 180゛.

Y-ROMII is a luminance component ROM.

The level controller 12 is a part in which the FM-exchanged data level is controlled by the original numerical data according to a bell filter constant, and becomes a digital bell filter.

The delay circuit 13 is used to allow the Y data to take the same time as the time the DR and DB pass through the FM exchange bevel filter.

The adder 14 is an adder that adds chroma data and Y to produce a video signal.

The D/A converter 15 converts the digital output of the adder 14 into a D/A converter 15.
A conversion is performed to create an analog signal.

Since the synthesizer 16c, EQ, VSYNC, etc. are not written in the ROM data, they are used as external devices for synthesis.

LPF 17 is used to remove high frequency components.

Amplifier 18 is used to output a 75Ω VBS signal.

A SECAM signal can be created with the above configuration.

Since most of the circuits are the same as those for PAL, a unit exchange format may be used.

±550K when creating DR and DB memory with 12 bits
Since it expresses the band IIz, (1 step 268Hz
).

Also, if it is made with lO bit (l step 107482).

Since the SECAM standard is 2 KHz, 10-bit data is possible.

(Effects of the Invention) As described above in detail, according to the present invention, a color signal in the SECAM system can be created by digital processing, and a pre-emphasis/limiter can be used.

Frequency and bell filter adjustments are not required, and stability depends only on the reference clock, resulting in high stability. Therefore, it is highly effective when applied to the digitization of SECAM signal generators in general and FM signal generators.

[Brief explanation of the drawing]

Figures 1 (a) and (b) are side views of the bell filter characteristics and output waveforms used in the present invention, and Figures 2, 3, 4, 5, and 6 are FM conversion sections used in the present invention. 7 and 8 are block diagrams showing an example of the digital bell filter used in the present invention, and FIGS. (a)(b)(
C) and FIGS. 10(a), (b), and (C) are waveform diagrams for explaining the operation of pre-emphasis used in the present invention.
FIG. 1 is a block diagram showing an example of a configuration for implementing the present invention. Patent applicant Shiba Sori Co., Ltd.

Claims (1)

[Claims] The Y signal, the R-Y signal, and the B-Y signal are stored in a memory as pre-emphasized digital values, and the R-Y signal and the B-Y signal read from the memory are subjected to digital FM conversion. The converted output is subjected to sine wave conversion, the Y signal read from the memory is added to the converted output, and the added output is digital-to-analog converted to obtain a SECAM color signal converted into an analog signal. A method of digitally creating color signals using the SECAM method, which is characterized by