JPS5936475B2 - Signal generation circuit in color television system - Google Patents

Description

Detailed Description of the Invention The color subcarrier frequency fsc of a color television system called the PAL system (hereinafter referred to as TV) has a horizontal scanning frequency fh = 15625 Hz and a vertical scanning frequency f. =50Hz, the following (1)
Frequency shown by the formula fscfsc=(282--)fh
+J=4433618.75H2・・・・・・・・・
(1).

Therefore, the color subcarrier frequency fs in the PAL system
The frequency relationship between c and horizontal scanning frequency fh is 70
9379fh=2500fsc... (2) Since it is as shown in equation (2) above, horizontal scanning can be performed even if the color subcarrier frequency fsc or its integral multiple frequency value is simply divided. 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 1800 degrees every horizontal scanning period, and a 1/4 line offset is used as interleaving between the color subcarrier and the horizontal scanning frequency. In addition, since an offset of fv/2 is added to make the cross color less noticeable, the color subcarrier frequency fsc in the PAL system has the following 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, the color subcarrier frequency is F8.

Horizontal scanning frequency Fh and vertical scanning frequency F with reference to
When generating V, it is necessary to add two frequency offsets -Fh/4 and fv/2.
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 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 generator 3 of various pulses having horizontal and vertical scanning periods described above divides the input reference frequency signal having a frequency value of 284fh at a predetermined frequency division ratio, and
Waveform shaping is performed to generate horizontal and vertical synchronizing pulses, blanking pulses, clamp 'f 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, 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, which 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 subtracts the subtraction result signal to the first frequency subtracter 2. Give as a signal.

Therefore, in the first frequency subtracter 2, the minuend signal (284fh) given to it and the subtrahend signal {(Fh/
4) subtraction with one (Fv/2)}, i.e., (284f
h)-{(Fh/4)-(Fv/2)}-{(284-
1/4)Fh+(Fv/2) By performing the subtraction shown in the above equation, a color subcarrier having a frequency value as 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, it is not easy to obtain a bandpass filter with a steep cutoff characteristic at low cost [In order to raise the frequency band, {284fh)− (Fv/
2)}, the sidebands in the fractional band become closer to each other, so adopting such a method will not solve the problem.] Therefore, as in the conventional example circuit shown in Figure 1, , two frequency subtractors, namely, first and second frequency subtracters 2
, 6, the conventional signal generating circuit has a complicated 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. However, since the performance of the PAL signal generator was significantly inferior, the appearance of a signal generator for the PAL system that had sufficiently high performance and was inexpensive was long awaited.

The present invention provides a color TV system signal generating circuit which has a simple configuration and which satisfactorily solves the problems of the conventional signal generating circuits described above. The specific contents of the color T type signal generation circuit of the present invention will be explained in detail with reference to FIG. 2 of the accompanying drawings. PAL system color subcarrier frequency F8. and,
The relationship with the horizontal scanning frequency Fh is as shown in the above-mentioned equation (1). Color subcarrier frequency F, c=4
433618.75Hz and horizontal scanning frequency Fh=156
There is a relationship between the frequency and 25Hz as shown in equation (2) above, that is, 709379fh=25
00fsc...The relationship of equation (2) holds true.

In the color TV system signal generation circuit of the present invention,
The above-mentioned (
By setting the frequency relationship in equation 2) to that shown by the relationship in equation (3) above, a signal generation circuit with a simple circuit configuration can be easily obtained. The signal generation circuit for the color TV system of the present invention shown in the figure has the relationship between the frequency of the color subcarrier and the horizontal scanning frequency, which is obtained by modifying the above equation (3) as shown in the following equation (3-1). is a frequency equal to the normal frequency Fsc of the color subcarrier in the PAL system = 4433618.75Hz,
Alternatively, the circuit configuration is such that an output signal having a frequency that is an integral multiple of the reference frequency signal generator is outputted from the reference frequency signal generator.

In the signal generation circuit for the color TV system of the present invention shown in FIG. 2, 1a is a reference frequency signal generation circuit, where the frequency value of the color subcarrier in the PAL system is Fsc, and n When Nfsc is an integer, an output signal whose frequency value is represented by Nfsc is generated and is applied to the frequency divider 8 and the frequency subtracter 2a. The frequency divider 8 divides the signal whose frequency value is n'f given to it by 1/n, and then divides the signal whose frequency value is f, that is, the regular color subcarrier frequency (4
433618.75 Hz) to the output terminal 11.

In addition, the frequency subtracter 2a described above uses the signal of the frequency value Nfsc given to it from the reference frequency signal generation circuit 1a as the subtracted signal, and also uses the frequency value given to it from the 1/161 frequency divider 7 (282nf1! ./16
The signal of 1) is sent as a subtraction signal, and the subtraction shown in the above equation (3-1) is performed, and the frequency value becomes 282nfh'(
Fh' represents a frequency extremely close to the horizontal scanning frequency Fh of the PAL system).

Frequency value 282nfK from the frequency subtractor 2a described above
The output signal of 1/161 frequency divider 1 and 1/n frequency divider 9
The output signal of the 1/161 frequency divider 1 is subtracted to the frequency subtractor 2a as described above. Also, the 1/n frequency divider 9 receives the frequency value 282fI! as a signal. , is frequency-divided by 1/n to produce a signal with a frequency value of 282fh, that is, a frequency value that is extremely close to the frequency value of the color subcarrier of the SECAM method (a frequency value that indicates an error within the allowable error range according to the broadcasting standard). ) is output to the output terminal 12.

In addition, in the pulse generator 3, the horizontal scanning frequency FK = 1562, which has a slight error within the allowable range with respect to the normal horizontal scanning frequency Fh = 15625Z in the PAL system.
A signal of 5.0026 Hz is sent to the output terminal 13, and the normal vertical scanning frequency Fv=5 in the PAL system is sent.
In addition to sending out to the output terminal 14 a signal with a vertical scanning frequency f↓=50.0000083 Hz that has a very small error within the allowable range with respect to 0 Hz, it also has a very small error within the allowable range as described above. Other signals of the horizontal and vertical scanning period (eg, blanking signals, clamp signals, gating signals, etc.) are also sent to the output terminals.

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 subtracter, 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 signal generating circuit for a conventional color TV system, and FIG. 2 is a block diagram of a signal generating circuit for a color TV system according to the present invention. 1, 1a...Reference frequency signal generator, 2, 2a
, 6... Frequency subtractor, 3... Horizontal,
Generator of various pulses having a vertical scanning period (pulse generator), 4, 5, 7 to 9... Frequency divider, 11 to 14
...Output terminal.

Claims (1)

[Claims] 1 Frequency value is nf_s_c, where n is an integer, f_s
_c is the frequency of the PAL color subcarrier), and the frequency value generated by the reference frequency signal generating means is nf.
1/n frequency division means for dividing the reference frequency signal of __s_c to 1/n to obtain a PAL color subcarrier, and the frequency value generated by the reference frequency signal generation means is nf_s_c.
The reference frequency signal of is given as the minuend signal, and the frequency value is 282nf'_h/161 (however, f
'_h is a frequency approximating the horizontal scanning frequency fn of the PAL system) is given as a subtraction signal, nf_s_c-(282nf_h'/161)
= 282nf_h', the frequency value becomes 28
A frequency subtraction means for generating an output signal of 2nf_h′ and a frequency value outputted from the frequency subtraction means are 28
1/161 frequency division means that divides the frequency of the output signal of 2nf_h' to 1/161, and the frequency value output from the 1/161 frequency division means is (282nf_h'/161).
By supplying the output signal from the frequency subtraction means to the frequency subtraction means as a subtraction signal, and the output signal from the frequency subtraction means, the frequency approximates the horizontal scanning frequency f_h and vertical scanning frequency f_v of the PAL system. value f_
A signal generation circuit in a color television system comprising means for obtaining a horizontal scanning frequency signal, a vertical scanning frequency signal, etc. having h' and f_v', respectively.