JPS6011516B2 - Signal generation circuit in color television system - Google Patents

Description

Detailed Description of the Invention The frequency f of the color subcarrier of the color television system called the PAL system (hereinafter, color television is abbreviated as TV) is the horizontal scanning frequency f, fh=1562.
m using 5 days 2 and vertical scanning frequency fv=50Hz.
Frequency value f expressed by the formula = (284-ki)fh+
It is defined as having ki = 443361875Hr-...m.

Therefore, the frequency relationship between the color subcarrier frequency f and the horizontal scanning frequency fh in the PAL system is 709
37 balls h = 250 is sc...'' [21 Since it is shown in the above formula [2}, the color subcarrier frequency f
The horizontal scanning frequency fh and the vertical scanning frequency fv cannot be obtained by simply dividing the frequency value of Sc or its integral multiple.

That is, in the PAL system, the modulation polarity of one of the color signal modulation axes is inverted by 180 degrees every horizontal scanning period, and the 1'4 line offset method is used for interleaving the color subcarrier and horizontal scanning frequency. In addition, since an offset of fv/2 is added to make the cross color less noticeable, the color subcarrier frequency f in the PAL system is shown in the above equation '11. This is because a frequency offset of 1'Q of the horizontal scanning frequency fh and 1'2 of the vertical scanning frequency fv is provided.

Therefore, in the various signal generation circuits used in the PAL system, when generating the horizontal scanning frequency fb and the vertical scanning frequency fv using the color subcarrier frequency f as a reference, two signals, fh/4 and fv/2, are used. A frequency offset is required.

Conventionally, the above-mentioned two frequency offsets are most commonly used as shown in the first diagram.

Since this was achieved by the use of two frequency subtracters as shown in the diagram, various problems as described below could not be avoided. That is, FIG. 1 is a block diagram showing an example of the configuration of a conventional signal generation circuit in the PAL system. In this FIG. A signal having a frequency value of 284fh is given to the first frequency subtractor 2 as its minuend signal, and is also given as a reference signal to the generator 3 of various pulses having horizontal and vertical scanning periods.

The various pulse generators 3 having the horizontal and vertical scanning periods described above divide the input reference frequency signal having a frequency value of 284fh at a predetermined frequency division ratio, and also perform waveform shaping to generate horizontal and vertical scanning signals. Generates vertical synchronization pulses, blanking pulses, clamp pulses, gate pulses, and other necessary pulses having horizontal and vertical scanning periods.

Among the output signals from the pulse generator 3, the signal having the horizontal scanning frequency fh is divided into 1/4 by the frequency divider 4, thereby becoming a signal with a frequency value of fh/4. The signal which is given to the frequency subtracter 6 of No. 2 as a catastrophic number signal and which has the vertical scanning frequency fv among the output signals from the pulse generator 3 is divided into 1/2 by the frequency divider 5. As a result, the frequency value is made into a signal of fv/2, and the signal is given to the second frequency subtracter 6 as a subtraction signal.

The second frequency subtracter 6 performs subtraction of {(fh/4)-(fv/2)} using the two signals, and sends the subtraction result signal to the first frequency subtracter 2 as a subtraction signal. give as.

Therefore, the first frequency subtractor 2 subtracts the minuend signal (284fh) applied thereto and the subtrahend signal {(fh no 4) - (fv/2)}, that is, (284L
)1{(fhノ4)-(tV/2)}ni{(284-1
'4) fh+(fY/2)} By performing the subtraction shown in the above equation, a color subcarrier having a frequency value as shown in equation '11 is sent out as an output signal.

By the way, in general, as a frequency subtracter, a configuration in which a double-balanced modulator or a balanced modulator is combined with a single sideband removal filter is used. The configuration is complex, and especially when a double-balanced modulator is used, an even more complex configuration is inevitable. Since the frequency of the fh band) is close to the required output frequency, it is necessary to provide a band waver with a steep cutoff characteristic in the output circuit of the balanced modulator. 4) - (fv/2)} is a low frequency value, so it is not easy to obtain a band waver with steep cutoff characteristics at low cost [In order to raise the frequency band, { (284fh) one (fv
/2)}, the sidebands at Hibijo become increasingly close to each other, so adopting such a measure will not solve the problem.] Therefore, the conventional example circuit shown in Figure 1 As such, the conventional signal generating circuit using two frequency subtracters, that is, the first and second frequency subtracters 2 and 6, has a complex and expensive structure as a whole.

Therefore, in the past, when constructing a low-cost signal generator for the PAL system, an attempt was made to adopt a method of omitting the fv/2 frequency offset described above, but signal generation using such a method is not possible. Since the PAL signal generator was significantly inferior in terms of performance, the appearance of a signal generator for the PAL system that had sufficiently high performance and was inexpensive was long awaited.

The color TV system signal generation circuit of the present invention provides a signal generation circuit that has a simple configuration and that satisfactorily solves the problems of the conventional signal generation circuits described above. The specific contents of the color TV system signal generation circuit of the present invention will be explained in detail with reference to FIG. 2 of the accompanying drawings.

The relationship between the color subcarrier frequency fsc of the PAL system and the horizontal scanning frequency fh is as shown in the above-mentioned formula [11], and the color subcarrier frequency fsc = 4433618
．． There is a relationship between the frequency values of 75Hz and the horizontal scanning frequency fh=15625Hz as shown in the equation (2), that is, sr of the 70937 group h=250...[21
The relationship of the formula is established.

In the color TV system signal generation circuit of the present invention,
PAL system color subcarrier frequency f and horizontal scanning frequency f
In particular, the frequency relationship of equation (2) above, which shows the correct frequency relationship between h and (282×162)nfh≠
161nfsc (however, n=1, 2, 3………)
...[3' By establishing the relationship shown by the above equation {3}, it is possible to easily obtain a signal generation circuit with a simple circuit configuration, and the present invention shown in FIG. In the signal generation circuit of the color TV system, the relationship between the frequency of the color subcarrier and the horizontal scanning frequency obtained by transforming the above-mentioned glue equation as shown in the following equation (3-1) is the horizontal scanning frequency of the PAL system. This is realized in a circuit configuration in which an output signal having a frequency equal to the normal frequency fh=15625 days 2 or an integral multiple thereof is output from the reference frequency signal generator.

28 or fh. nfSc 11. ．． (3-1) In the signal generation circuit for the color TV system of the present invention shown in FIG. When the value is fh and n is an integer, an output signal whose frequency value is expressed as 28 or f is generated, and it is sent to frequency divider 7 and frequency divider 9 to calculate the horizontal and vertical periods. A generator 3 (pulse generator 3) of various pulses is provided.

The tube divider 9 divides the fh signal with a frequency value of 28 given to it to 1/n, and then divides the fh signal with a frequency value of 28
A signal, that is, a color subcarrier having a regular frequency value in the SECAM method, is sent to the output terminal 12.

The output terminal 13 of the pulse generator 3 outputs a signal with a normal horizontal scanning frequency fh=15625Hz in the PAL system, and the output terminal 14 of the pulse generator 3
From then, the normal vertical scanning frequency fv in the PAL system is
A 50 Hz signal is output, and other signals (eg, planking signal, clamp signal, gate signal, etc.) with horizontal and vertical scanning periods are also output from other output terminals of the pulse generator 3. Further, the frequency divider 7 described above converts the signal whose frequency value given to it is 28 or fh to 1/I61
The signal divided into two cylinders (28/161) is passed through the phase discriminator P.
D as a reference signal. give.

In Figure 2, LPF is a low-pass waveform device (low-pass waveform device).
, VCO is a voltage controlled oscillator, and the voltage controlled oscillator VCO described above oscillates with the frequency value of nf& as the center frequency, and provides an output signal therefrom to the frequency divider 15. The frequency value of f& described above is a frequency extremely close to the frequency value fsc of the color subcarrier in the PAL system. The frequency divider 15 described above divides the frequency nf & of the output signal of the voltage controlled oscillator VCO supplied thereto by 1/162 (nf
c) The output signal of /162 is given to the above-mentioned phase discriminator PD as its comparison signal.

The output signal from the phase discriminator PD is supplied as a control signal to the voltage-controlled oscillator VCO via the low-pass waveform filter LPF, so that the center frequency value of the voltage-controlled oscillator VCO is the same as that of the PAL color subcarrier. A signal with a frequency value nfic extremely close to n times the frequency fsc is output, and the output signal is given to the frequency divider 8 and also to the frequency divider 15 as described above.

The frequency divider 8 divides the signal with the frequency value nfc given to it by 1/n to produce a signal with a frequency value fm, that is, a frequency extremely close to the frequency value of the color subcarrier in the PAL system. A signal with the value f x c is output to the output terminal 11.

In the color TV system signal generation circuit of the present invention configured as described above, from the reference frequency signal generator lb,
Regular horizontal scanning frequency fh=156 in PAL system
n times 25Hz (n=1, 2, 3,...
...), the output terminal 13 of the pulse generator 3 outputs the normal horizontal scanning frequency fh=1 in the PAL system.
A signal of 5625Hz is output, and the pulse generator 3
A signal with a normal vertical scanning frequency fY = 50 Hz in the PAL system is output from the output terminal 14 of the PAL system, and other signals with horizontal and vertical scanning periods (for example, planking signal, clamp signal, gate signal, etc.) are also output. The output terminal 12 outputs a color subcarrier having a regular frequency in the SECAM system, and the output state 11 shows the color subcarrier in the PAL system. the normal frequency value of the carrier wave,
In other words, the frequency value 4433618.012HZ has an extremely small frequency difference within the allowable range for the frequency value 4433618.75HZ (with an error of 10.738HZ).
) signal is output.

As described above, the signal generation circuit for the color TV system of the present invention can easily realize the frequency offset of the color subcarrier of the PAL system, and also has a simple configuration and can be easily integrated into a color TV system. According to the present invention, the various problems of the conventional circuit described above can be satisfactorily solved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a signal generation circuit for a conventional color TV system, and FIG. 2 is a block diagram of a signal generation circuit for a color TV system according to the present invention. 1, lb...Reference frequency signal generator, 2,6.
... Frequency subtractor, 3... Generator of various pulses having horizontal and vertical periods (pulse generator), 4, 5,
7 to 9, 15... Frequency divider, PD... Phase discriminator, LPF... Low frequency monkey wave filter, VC0...
...Voltage controlled oscillator, 11-14... Output terminal. Atsushi 1 Diagram Chrysanthemum 2 Diagram

Claims (1)

[Claims] 1 The frequency value is 282nf_h (where n is an integer, f
_h is the horizontal scanning frequency of the PAL system); a reference frequency signal generating means for generating a reference frequency signal of the horizontal scanning frequency of the PAL system; 161 frequency dividing means, and the center frequency value is nf'_s_c (however, f'
__s_c is the frequency f_s_c of the color subcarrier in the PAL system
a voltage controlled oscillator that generates a signal with a frequency approximating , a 1/162 frequency dividing means that frequency divides the output signal of the voltage controlled oscillator to 1/162, and an output from the 1/162 frequency dividing means. The frequency nf_s_c/162 and 1 of the output signal from the 1/162 frequency dividing means are determined by the phase discrimination output obtained by performing phase discrimination between the signal and the output signal from the 1/162 frequency dividing means. /161 frequency dividing means for controlling the voltage controlled oscillator so that the frequency of the output signal from the voltage controlled oscillator is equal to 282nf_h/161;
By being supplied with the output signal of the reference frequency signal generating means and the 1/n frequency dividing means for dividing the frequency by n and outputting the PAL color subcarrier having a frequency of f'_s_c, the PA
Horizontal scanning frequency f_h and vertical scanning frequency f_v of L method
1. A signal generation circuit in a color television system comprising means for obtaining a signal having a horizontal scanning frequency and a signal having a vertical scanning frequency.