JPS5936476B2 - Signal generation circuit in color television system - Google Patents

Description

[Detailed Description of the Invention] The frequency fsc of the color subcarrier of the color television system called the PAL system (hereinafter, television is abbreviated as TV) is the horizontal scanning frequency fh = 15625 z and the vertical scanning frequency. Using fri-■ 5Oll2, the frequency value ffsc■(284--) is expressed by the following equation (1).
fh+"■4433618.75H2...
...It is defined as having (1).

Therefore, the color subcarrier frequency fs in the PAL system
The frequency relationship between c and horizontal scanning frequency fh is 70
9379fre ■ 2500fsc... (2) Since it is as shown in equation (2) above, even if you simply divide the color subcarrier frequency fsc or its integral multiple frequency value, it will not be horizontal. Scanning frequency fh and vertical scanning frequency fv
cannot be obtained.

That is, in the PAL system, the modulation polarity of one of the color signal modulation axes is inverted by 18 OPs every horizontal scanning period, and the 1/4 line offset method is used for interleaving the color subcarrier and horizontal scanning frequency. is applied, and an offset of fv/2 is added to make the cross color less noticeable, so the color subcarrier frequency fsc in the PAL system is shown in equation (1) above. This is because a frequency offset of 1/4 of the horizontal scanning frequency fh and 1/2 of the vertical scanning frequency fv is added.

Therefore, in the various signal generation circuits used in the PAL system, when generating the horizontal scanning frequency Fh and vertical scanning frequency Fv using the color subcarrier frequency fsc as a reference, two frequency offsets of -Fh/4 and fv/2 are required. It is necessary to attach.

Conventionally, the two frequency offsets mentioned above have most commonly been obtained by using two frequency subtracters as provided in the block diagram shown in Figure 1. It was not possible to avoid various problems such as those mentioned above.

That is, FIG. 1 shows a block diagram of an example of the configuration of a conventional signal generation circuit in the PAL system, and in this FIG. A signal having a frequency value of 1 to 284 fh is given to the first frequency subtractor 2 as its minuend signal, and is also given as a reference signal to a generator 3 of various pulses having horizontal and vertical scanning periods.

In the various pulse generators 3 (pulse generators 3) having the horizontal and vertical scanning periods described above, the 28
The reference frequency signal having a frequency value of 4fh is divided by a predetermined frequency division ratio, and the waveform is shaped to generate horizontal, vertical synchronization pulses, blanking pulses, clamp pulses, gate pulses, etc. , generates the necessary pulses and signals having a vertical scanning period.

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, so that the signal has a frequency value of Fh/4. The signal having the vertical scanning frequency Fv among the output signals from the pulse generator 3 is given to the second frequency subtractor 6 as a subtracted signal.
By dividing the frequency into Fv/2, the frequency value is made into a signal of Fv/2, and is given to the second frequency subtracter 6 as a subtraction signal.

The second frequency subtracter 6 subtracts {(Fh/4)−(Fv/2)} using the two signals, and the subtraction result signal is sent to the first frequency subtractor 2.
as a subtraction signal.

Therefore, in the first frequency subtracter 2, the minuend signal (284fh) given to it and the subtrahend signal {( Fh
/ 4 ) - ( Fv / 2 )}, that is, ( 284fh) - { ( Fh / 4 ) - ( Fv
/ 2)}={(284-1/4)Fh+(Fv/2
) By performing the subtraction shown in the above equation, the color subcarrier having the frequency value shown in equation (1) 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. is complex, and especially when a double-balanced modulator is used, an even more complex configuration is unavoidable. ) is close to the required output frequency, it is necessary to provide a bandpass filter with a steep cutoff characteristic in the output circuit of the balanced modulator. 1 (Fv/2)} is low, so it is not easy to obtain a bandpass filter with steep cutoff characteristics at low cost. -(Fv
/2)}, the sidebands in the fractional band become closer to each other, so even if such a method is adopted, the problem will not be solved.''Therefore, the conventional circuit shown in Figure 1 is Furthermore, 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, when constructing a low-cost signal generator for the PAL system, an attempt has been made to employ a method of omitting the frequency offset of Fv/2 described above, but signal generation using such a method has been difficult. 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 signal generator circuit for the color TV system 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 and the horizontal scanning frequency Fh in the PAL system is as shown in equation (l) above, and the color subcarrier frequency Fs,c
=4433618.75Hz and horizontal scanning frequency Fh=1
There is a relationship between the frequency value of 5625Hz and that shown in equation (2), that is, 709379fh-
2500f86...The relationship of equation (2) holds true.

In the color TV system signal generation circuit of the present invention,
PAL system color subcarrier frequency F8.

The frequency relationship of equation (2) above, which indicates the correct frequency relationship between
82×162)Nfh+161nf80 (however, n=
1, 2, 3...) ... (3) By setting the relationship shown in equation (3) above, a signal generating circuit with a simple circuit configuration can be easily obtained. The color TV system signal generation circuit of the present invention shown in FIG. A frequency whose relationship with the frequency is equal to the normal frequency F8O-4433618.75Hz of the color subcarrier in the PAL system,
Alternatively, the reference frequency signal generator may be implemented in a circuit configuration in which an output signal having a frequency that is an integral multiple of the reference frequency signal generator is output. In the color TV system signal generation circuit of the present invention shown in FIG.
and when n is an integer, the frequency value is 2820fh
It generates an output signal as represented by , and sends it to the frequency divider 7, the frequency adder 10, the 1/n frequency divider 9, the horizontal,
Generator 3 of various pulses of vertical scanning period (Pulse generator 3
) and give to. The frequency divider 7 divides the applied signal having a frequency value of 282nfh to 1/161, and then provides a signal having a frequency value of 282nfh/161 to the frequency adder 10.

Therefore, in the frequency adder 10 described above, the frequency value 282n given to it from the reference frequency signal generation circuit 1b is
Frequency addition is performed on the fh signal and the frequency value (282nfh/161) signal given to it by the 1/161 frequency divider 7 as shown in equation (3-1), and the frequency value is An output signal of Nf<o (f<o represents a frequency very close to the normal frequency F8O of the color subcarrier in the PAL system) is output.

Frequency value Nf2 from the frequency adder 10 described above.

The output signal is supplied to the 1/n frequency divider 8 and divided into 1/n, and from the 1/n frequency divider 8, a frequency approximate to the frequency F8O of the color subcarrier of the PAL system is 4433618.75 Hz. f2. -4433618.012Hz (error is -0
．． 738Hz) is sent to the output terminal 11. Further, the 1/n frequency divider 9 to which the signal of the frequency value 282nfh from the reference frequency signal generator 1b is supplied divides the applied signal of the frequency value 282nfh to 1/n, A signal with a frequency value of 282fh, that is, a signal with a frequency value of the color subcarrier of the SECAM system is outputted to the output terminal 12, and a signal with a frequency value of 282nf from the reference frequency signal generator 1b described above is also supplied. A generator 3 (pulse generator 3) of various pulses with horizontal and vertical scanning periods sends a signal with a regular horizontal scanning frequency Fh-15625Hz in the PAL system to an output terminal 13, and also outputs a signal with a regular horizontal scanning frequency Fh-15625 Hz in the PAL system. In addition to sending a signal with a frequency of Fv=50Hz to the output terminal 14, a signal with a horizontal and vertical scanning period (for example, a blanking signal,
clamp signal, gate signal, etc.) are also sent to the output terminal.

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 for the PAL system, and has a simpler configuration than the frequency subtracter used in the conventional circuit. Since it is easy and only requires the use of one frequency adder, the present invention can satisfactorily solve the problems of the conventional circuits described above.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional color TV system signal generating circuit, and FIG. 2 is a block diagram of a color T system signal generating circuit of the present invention. 1, 1b...Reference frequency signal generator, 2, 6...
... Frequency subtractor, 3 ... Various pulse generators (pulse generators) having horizontal and vertical scanning periods,
4, 5,? ~9... Frequency divider, 10...
Frequency adder, 11-14... Output terminal.

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), and the frequency value generated by the reference frequency signal generating means is 282nf_
h reference frequency signal is divided into 1/161 and the frequency value is 2.
1/161 which generates an output signal of 82nf_h/161
A frequency dividing means, a reference frequency signal having a frequency value of 282nf_h generated by the reference frequency signal generating means, and a reference frequency signal having a frequency value of 282nf_h generated by the aforementioned 1/161 frequency dividing means.
By supplying the nf_h/161 signal, 2
82nf_h+(282nf_h/161)=f'_s
By performing frequency addition of _c, the frequency value becomes nf'_s_
a frequency addition means for generating an output signal of c, and a frequency value outputted from the frequency addition means is nf'_s_c
The frequency of the output signal of is divided by 1/n to obtain a frequency f that approximates the frequency f_s_c of the color subcarrier in the PAL system.
By supplying means for obtaining an output signal of '_s_c and an output signal having a frequency value of 282nf_h from the reference frequency signal generating means, horizontal scanning having a horizontal scanning frequency f_h and a vertical scanning frequency f_v of the PAL system, respectively. A signal generation circuit in a color television system, which is a means for obtaining frequency signals, vertical scanning frequency signals, etc.