DE4127813A1 - SECAM colour video signal generator with pre-emphasis circuit - applies transformation from frequency modulation phase value to sine-wave in course of digital processing of signal - Google Patents

Abstract

An incoming video code (1) is decoded (16) by a circuit which provides pre-emphasis by digital means so that only additions (5,10) are required in subsequent signal processing, and complex multiplications are avoided. Fundamental frequency pre-emphasis data are generated by addition (5) with delay (8) by one clock period, and shift, complement or noncomplement feedback. FM signal is phased (10,11) and transformeed (12) into a sine value for D/A conversion (13). ADVANTAGE - Less costly equipment, insensitive to influences of manufacture process, temperature or voltage, and achieves maximum reliability and stability without fine-tuning components or compensation.

Description

Television systems are generally classified into three types in the world sified: NTSC, PAL and SECAM. They differ at all mainly in modulation processes for color signals, in addition to their differences in bandwidth, the number of their samples lines and refresh rates. For NTSC and PAL systems systems use color signals, amplitude and phase modulations, which are much easier. For the SECAM system, the Fre frequency modulation used and difficulties with this modula tion are that SECAM color signal frequencies within a wide range (3.9 MHz-4.75 MHz) vary and that the accuracy of the two band center frequencies (4.25 MHz ± 2 KHz and 4.40625 MHz ± 2 KHz) is very critical and accurate and therefore not accessible for ordinary modulation circuits is.

The following modulation methods for SECAM systems are known:

• 1. The use of a voltage controlled oscillator: The This method consists of controlling an input voltage to use oscillator frequencies, which is very sensitive against environmental influences (temperature, air humidity speed), the supply voltage and the components. Out for this reason, its stability and reliability are poor and fine tuning or feedback circuits must be used to meet SECAM system specifications. Because of this, it is practically impossible to do this procedure to use for commercial production, and quality is moderate.
• 2. The use of a voltage controlled oscillator and a phase-locked loop: This type of circuit designs is very common with analog circuits such as B. the Philips TDA 2506, 2507 and eini gene manufactured by Sony integrated circuits (IC's). With  This method can be used to obtain the required specifications are sufficient, but the follow-up synchronization used here and complex adjustment and compensation resulted in connection with its difficult implementation at high costs of commercial production.

They also require well known digital filters techniques considerable arithmetic calculations and for the Video signal processing would be the design of well-known digital files ter very complicated, so that one must have doubts whether digital Procedures are really easier than analog procedures.

Description of the present invention

The present invention seeks to address the problems of State of the art to solve by using the digital oscillator Theory is used to describe words or graphs convert into standard interface signals as they are for a SECAM TV system are required, the required Words and graphics of SECAM TV reception directions are reproduced as soon as these signals by sol che receiving devices are received. The present Er can also be found in video tape recorders, TV game ap paraten and personal computers are used and used a digital oscillator for frequency modulation, so that at Pre-emphasis required for SECAM systems can also be achieved by using digital system.

Fig. 1 is a block diagram of an embodiment of the device for generating a color signal for SECAM systems according to the present invention.

Fig. 2 is the waveform (wave-shape) of the output angle (output angle) according to the present invention.

FIG. 3 is the waveform of the output voltage according to the present invention corresponding to FIG. 2.

Fig. 4 is the return waveform according to the present invention corresponding to Fig. 2 and when n X wL π.

Fig. 1 shows the color code input 1 , registers 2 , 8 and 11 , the first decoder 3 , the second decoder 4 , adders 5 and 10 , the first multiplier 6 for transposition (multiplication by 1/2 in the exemplary embodiment), the second multiplier 7 for transposition (multiplication by 1/4 in the exemplary embodiment), the frequency control signal of the digital oscillator 9 , with tel for the sine wave transformation 12 , digital / analog converter 13 and the output color signal f of the SECAM system 14 .

The pre-emphasis process in this invention is to have a decoder 16 provide some of the computation functions and that only subsequent additions are required for subsequent signal processing to avoid complicated multiplications.

The preprocessing required in SECAM systems (pre-empha sis) has the following characteristics:

where f ₁ = 85 KHz, f = Chromanznanzfrequenz, A (f) = transfer function, which is represented by the Laplace transform by:

S = complex frequency

is.

Furthermore, the transition from the transfer function to the Laplace transform for the transfer function of the Z transform tion digital preprocessing (pre-emphasis) realized.  

This results in the transfer function of the Z transformation as:

or

in which

If K = 7, (f _s = 5.6 MHz), the denominator of A (Z) will be (1-0.75 Z ^-1 ); no multiplier is required for the coefficient of 0.75 and therefore only transposition and addition are used. This denominator process can be realized by adding 5 , the first multiplier 6 , the second multiplier 7 and register 8 in Fig. 1, while the numerator of A (Z) by register 2 , the first decompression of 3 and the second Decoder 4 in Fig. 1 can be realized.

Said decoders can generate a delay effect in addition to functions as a frequency comparison table. The second decoder creates a delay by one clock unit. In addition, the frequency comparison table for the first decoder 3 and the second decoder 4 was multiplied by different coefficients, so that the subsequent data processing does not require any multiplication.

The decoding device 16 comprises the first decoder 3 , the second decoder 4 and register 2 in order to generate frequency data which correspond to the color code 1 .

By their interaction, the register 2 , the first decoder 3 , the second decoder 4 , the adder 5 , the first multiplier 6 , the second multiplier 7 and register 8 in FIG. 1 produce and receive the decoding of the color code and the preprocessing functions the output Yi (9) from the input color code Xi (1) to control the digital oscillator.

A sampling frequency close to 5.6 MHz is good enough. For this reason, as far as f _{s is} concerned, the requirements of graphic systems must also be taken into account. Sampling frequencies, which are normally used for graphic systems, are 1.5 times the 3.58 MHz of the NTSC carrier frequency and 6/5 times the 4.43 MHz of the PAL B carrier frequency.

These two frequencies are very close to each other and at 5.3 MHz.

The use of a sampling frequency of 5.3 MHz for graphic Systems is also appropriate for NTSC, PAL and SECAM systems and can be used worldwide as long as only different Color signal generators are used.

5.3 MHz produces very small errors. The correct formula for the denominator of A (Z) is (1-0.74 Z ^-1 ), which produces very small errors compared to the formula of the exemplary embodiment (1-0.75 Z ^-1 ). It is further preferred that f _{s be} an integer multiple of the horizontal sampling frequency in order to obtain correct horizontal sampling frequencies.

In the exemplary embodiment, f _{s is selected} as 341 times the horizontal sampling frequency, ie 5.32815 MHz.

A change of the 1/2 or 1/4 shift operation of the first multiplier 6 and the second multiplier 7 in the exemplary embodiment to 1 or -1/4, or the addition of a further addition and further shift operations to minimize Errors or a change in the sampling frequency will not result in any changes in the implementation. If a negative coefficient such as For example, if -1/4 is implemented, a shift and a feedback of the obtained complement will be good enough.

In Fig. 1, the digital oscillator portion between the Yi (9) input and the color signal f (14) output is arranged.

Here, adder 10 and register 11 form an accumulator, and Yi (9) is the accumulated number (input signal).

If the accumulator overflows, the carry is given, whereby the content of the accumulator corresponds to the phase angle of the oscillator. When the accumulator M bits, has a value of 2 ^M corresponds to the phase angle π 2.

Each accumulated Yi is equal to a binary integer and the smallest composite frequency is 2 ^-M fx, while Yi is 1 and f _{x is} the accumulated frequency or clock frequency for the digital oscillator.

2 ^-M f _x can also be called the resolution of the composite frequency; in other words, the composite frequency is an integer multiple of the resolution:

f = Yi2 ^-M f _x (6)

In the exemplary embodiment, f _x = 21.3125 MHz; in other words, the clock rate of the digital oscillator is 21.3125 MHz or four times the clock rate of the decoder / preprocessor. In order to obtain a sufficient resolution, one only has to choose the number M large enough. On the basis of the accuracy requirements of the SECAM system, M = 13 is set in this exemplary embodiment.

The formulas ( 6 ), ( 4 ) and ( 5 ) can be used to define the number of bits of the components of the preprocessing stage (pre-emphasizor) such as the adder and the register and the value to be stored in the decoder.

Fig. 2 shows the situation of the value in the register 11 which successively accumulated with Yi, that is, the output waveform (output wave-form) when the value is sent in register 11 directly to the digital / analog converter 13.

This waveform contains the second, third, fourth and fifth harmonic.

These Hamonic can be eliminated very easily with filters will; therefore we are not really concerned about this harmo niches, but the alias frequency spectrum, which is determined by the Ab keying is generated, d. H. fx-Nf, N = 2, 3, 4, 5,. . .

The function of the means for sine wave transformation 12 is to dampen or eliminate these harmonics. The most common method is to use a set of sine or cosine ROMs.

If a sine ROM or a cosine ROM is used between register 11 and digital / analog converter 13 , FIG. 3 shows the waveform of the generated output signal.

Since the output signal which is converted by a sine-ROM or a cosine-ROM contains no harmonics, the alias frequency spectrum which is generated by sampling will only be f _x -f). This frequency is a multiple of f and can therefore be isolated in a simple manner. For this reason, f _x must be chosen at least four times f.

In the present embodiment, a much simpler sine converter is designed by using the MSB of register 11 and other bits for one's complement ( 1 's complement), that is, by using an exclusive-or gate.

The value which is processed in this way has the output signal wave form as shown in FIG. 4 after it has passed through the digital / analog converter.

As a result, not only the odd harmonics are re reduced and the even harmonics eliminated, but the digital to analog converter is also enabled to Reduce bit, reducing the difficulty of implementation tion of digital / analog converters can be reduced.

If the harmonics are reduced, the alias frequency spectrum generated remains within a tolerable range. If f _x = 21.3125 MHz, no alias spectrum overlaps with 3.9-4.75 MHz, and since alias accumulations at f _x -5f or higher harmonics are all attenuated to less than -40 dB they have no visible interference.

According to the present invention, color signals for SECAM Systems generated by a digital oscillator and a digital one Preprocessing unit (digital pre-emphasis) are used, which has the following advantages:

• 1. Reliable accuracy and frequency modulation characters risks;
• 2. no errors that arise from the manufacturing process or environmental influences can result, and the frequency accuracy freely according to the needs of the developer (designer) be set;
• 3. There are no fine tuning circuits or compensations on elements required; and
• 4. The digital system is very simple and easy to use adapt to commercial production.

The present invention is very suitable for use in Ge advise on generating a color signal for SECAM systems.

Claims (6)

1. A device for generating a color signal for SECAM systems ( 15 ), comprising:
a decoder ( 16 ) for converting an input color code to preset frequency data suitable for digital processing;
a first adder ( 5 ) in conjunction with a register ( 8 ) for generating frequency data for fundamental frequency preprocessing, the addition process including a delay of the register data ( 8 ) by a clock period and with a displacement, complement or non-complementary feedback thereto first adder ( 5 ) is provided;
a second adder ( 10 ) in conjunction with a register ( 11 ) for generating the phase value of an FM signal which represents the frequency data of the preprocessing (pre-empha sis);
Means for sine wave transformation ( 12 ) for converting the phase value into a sine value or a value whose effect is similar to a sine; and
a digital / analog converter ( 13 ) for converting the sine value or a value similar to a sine into analog signals. 2. An apparatus for generating a color signal ( 15 ) suitable for SECAM equipment and used for decoding color codes and for providing fundamental frequency preprocessing, comprising:
a device for decoding ( 16 ) for generating frequency data corresponding to a color code ( 1 ), said device for decoding comprising a second decoder ( 4 ) in connection with a first decoder ( 3 ) and a register ( 2 ) for Generation of frequency data according to the color code of a previous clock cycle; and
an adder ( 5 ) in connection with a register ( 8 ) for generating preprocessed frequency data, the addition process of which includes a delay of the data of the register ( 8 ) by a clock unit, and with a shift, complement or non-complementary feedback to this Adder ( 5 ) is provided. 3. The device for generating a color signal according to claim 2, the decoders are of the PLA type and according to a time sequence work, which by the pixel clock given is. 4. A device for generating a color signal ( 15 ) for SECAM equipment, suitable for providing frequency modulation and driven by frequencies which are integer multiples of the pixel timing, comprising an adder ( 10 ) and a register ( 11 ) for generating a Phase value of an FM signal which represents the color pixel signal, the pixel timing being given by the sampling frequency;
means for sine wave transformation ( 12 ) for converting the phase value into a sine value or a value similar to a sine; and
a digital / analog converter ( 13 ) for converting the sinusoidal value or the value similar to a sinusoidal signal into analog signals. 5. The device for generating a color signal according to claim 4, in which the sine converter, the effect of which is similar to a sine value, through a set of exclusive-or-gates tern is realized. 6. The device for generating a color signal according to claim 4, in which the sine converter, the effect of which is similar to a sine value, through a set of exclusive NOR gates is realized.