CA1041657A - System for generating secam color carrier signals - Google Patents

Abstract

SYSTEM FOR GENERATING SECAM COLOR CARRIER SIGNALS

ABSTRACT OF THE DISCLOSURE
An oscillator signal approximately equal to 282 times the horizontal line frequency and a second oscillator signal approximately equal to 272 times the horizontal line frequency are each applied to frequency dividers, the output of the frequency dividers having a frequency substantially equal to the horizontal line frequency. A phase comparator compares the output of each frequency divider to a reference signal of horizontal line frequency. The first and second so-derived difference signals are applied through respective low pass filters to the respective oscillators thereby adjust-ing the frequency of the respective oscillators to be exactly 282 and 272 times the horizontal line frequency as required for the two color carrier frequencies respectively. In one embodiment the frequency division is carried out by binary frequency dividers. In other embodiments the frequency division is carried out by mixing the two oscillator frequencies with a signal having a frequency equal to 277 times the horizontal line frequency.

Description

5i7 1 The present invention relates to a ~ystem ~or ~urnishing a ~irst a~d second color carrier signal having qulescerlt frequenceis ~R and fOB equal to, respectively, 282 tiDles and 272 time~ the horizontal line frequency.
As is well k~own, in a SECAM color television system, the color carrier ls Irequency modulated O Thus a quartz o~cillator is ~ot suitable for generatin~ the color carrier signals~ On the other hand, the frequency of the color carrier signals must be constant, since otherwise a ~requency de~iation is interpreted at the rece~ver as a change in colorO For ~ is reason, the output of ~ e oscilla-tor which must of course be able to undergo freque~cy modu-lation, is co~pared at a time where the modulation is kno~n to be zero to a stable re~erence carrier ha~ing a ~requency `
~o and its freque~cy ad~sted accordingly. The toleran¢e for the frequency fo~3 fog of the color carrier signals is set to be ~ 2K~z, In order to optimize the compatilbility of the S~CA~ system, two di~erent ¢enter frequenlcie~ ~OR, ~OB
were used ~or the two dif~erence signals V'r and V'B.
The frequencies were set as ~ollow~: f~ ~ 15, 625 Hz;
fOR ~ 282 ti~es fH ~ 4040S25 ~Hz for the D'R
lines and fOB ~ times ~H = 4.25000 ~Hz ~or the D'B
lines.
Intercoupling of the two central ~requencie~ ~OR
and ~OB requires a great deal of equipment ln known S~CAM
apparatusO Slnce oscillator~ utilizing LC circuits ca~not in ge~eral achieve tolerances as small a~ + 2kHz for the center frequencies o~ the color televislon signals, the known ~ECAM
coders use two quartz filters which are activated by line - -frequency pulses~and oscillate only at frequencies (fOR

and ~OB) which are multiples ~ the horizontal line frequency.
~uch quartz f ilters are howcver, extremely expensive since they _2-,.............. . . .

1 find application only in SECAM equipment.
It is an object of the present invention to disclose a system for coupling the c ntral frequencies fOR and fOB of the color carrier signals to the horizontal line frequency in ac-cordance with the SECAM color television system. The system is `
to utilize commercially available building blocks which are rel-atively inexpensive The present invention is a system, in a SECAM color tel-evision system operating with a predetermined horizontal line frequency, serving to furnish a first and a second color car- ~q~
rier signal locked to the horizontal line frequency of the system, the first color carrier signal having a zero-modulation frequency ~
fOR equal to 282 times the horizontal line frequency, the second ~ .
color carrier signal having a zero-modulation frequency fOB equal to 272 times the horizontal line frequency, comprising, in combi- -nation, first oscillator means operative for generating a first oscillator signal constituting the first color carrier signal;
second oscillator means operative for generating a second oscil-lator signal constituting the second color carrier signal; means for furnishing a reference signal having a reference frequency related to the horiz~ntal line frequency and lower than fOR and fOBî frequency divider means connected to receive the first and ; " `
second color carrier signals and operative for producing first and second frequency-divided signals having frequencies substan~
tially equal to said reference frequency; comparator means con~
nected to receive the reference signal and the first and second `~
frequency-divided signals and operative for comparing the latter against the former to produce first and second difference signals; -and means for applying the first and second difference signals to said first and second oscillator means, respectively, for auto-matically adjusting the frequencies of the first and second color carrier signals to lock them on to the horizontal line frequency.
It is an advanta~ of the system in accodance with ~ j, . . . . . . , , ~ .
... . . . . .

1 this invention that commercially a~ailable elements su~h as quartz crystals and integrated circuits are util~zed.
The novel features which are considered as char-acterist~c for the invention are set fo~h in particular in the appended claims. The invention itself, however, both as to its coDstructionand its method of operation, together with ~:
addit10nal ob~jects and adva~tages khereof, will be best under stood from the following description of specific embodiments whe~ read in connection with th~ accompanying drawin~s:
F:IG. 1 is a block diagram oi a first embodiment of the present lnvention utilizing two ~requency dividers; :
FIG. 2 is a block diagram o~ a second embodiment of the prese~t invention using two mixer stages (transponder r n i le) p 1 c p FIG. 3 is a block diagram of a third embodiment of the present invention using a simplified circuit relative to t~e circuit o~ FI&. 2; and FIG. 4 is a block diagra~ of a fourth embodiment of the pre~ent ~nvention with a simplified circuit relative to ~ .

the block diagram of FIG. 1.
.

The preferred embodiments of the present invention will now be described with reference ~ the drawing.
. It should be n~ ed that corresponding elements in :
the different drawings have been given the same reference ~umbers.
FIG. 1 shows a first embodiment o~ the present in- , ve~tion. Two oscillators 1 and 2 oscillate, respectively, at a frequency substantially equal ~ 272 and 282 times the hori- ;~

zontal line frequency. The output frequency of oscillator 1 is regulated to the exact freque~cy foB by means of frequency divider means 3, comparator means 4, and low pass filter 5.

.~_ - . .: , .

i7 1 The signal ge~erated by oscillator 1, which is substantially but not exac~ y equal to the frequency fO~ = 272 x fH is frequenc~ divlded by means of frequency ~ivider 3 in the ratio of 1 : 272, so that the ~requency at the output of frequency divider 3 is substantially equal to the horiæontal line fre-quency. The pulse sequenc~ at the output of divider 3 is compalsed in phase comparator stage 4 with, a reference sig~al applied at a terminal 6. The refere~ce slgnal in the embcdi-ment of FIG. 1 has a frequency exactly equal to the horizontal line frequency. If there is a difference in frequency bet~een the signals applied at the two inputs of phase comparator 4, ;-~
a differe~ce signal is ~urni~hed which, a~ter filteri~g in low pass fllter 5, is applied to oscillator 1 in such a manner that its frequency is changed in such a direction as to drive the difference signal to zero. The signal at terminal 7, ;~
na~ely the signal at the output of oscillator 1 is thus con~
trolled to have the exact frequency fOB.
The frequency of ~scillator 2 is ~ milarly adjusted by ~requency divider 8, comparator 9 and low pass f ilter 10 ~ .
20 to be exac1~1y equal ~ the required color carrier frequency f~R ~282 times f~). Of course the frequency divider ratio o~
divider 8 is 1 : 282 rather 1 : 272. At terminal 11 a color carrier signal having a center frequency fOR ~ closely couplèd to the horizontal line frequency, is available.
Freque~cy dividers 3 and 8 comprise individual ~ ~
counter stages which are connected in cascade. me individual ~ g counter stages divide the frequency of the signals applied thereto i~ predetermined divider ratios. Thus frequency divider 3 divides frequency fog with the factors 272 ~ 16 x 17 =
2x2x2x2x17, These divider ratios are prime factors. Frequency divider 8 comprises counter stages having the following di-vider rat~os which are also prime factors: 282 = 2x3x47. Fre-.. . .

l 1(?4~ti57 1 quency dividers 3 and 8 can, in the preferred embodiments ofthe present invention, comprise lntegrated circuits ~hich are com~ercially avai lable .
It ~hould be no~ed that the frequency tolerances ~r the horlzontal llne ~requencies ~n SECA~ color televisio~
~y~tem6 ar~ relatively large so that ~uch a ~ide allowable ~reque~cy varlation in the horizontal l~ne frequency must be accommodated. For th~s purpose commercially available phase-lock-loop oircu~ts which are also economically advantageous 10 can read~ly be utilized. The dashed line in FIG. 1 shows such a circuit. They comprise an oscillator which may be regulated wlth respect to freque~cy, the low-pass filter 5 and the com-parator 4. The freque~cy d~vlder ratios furnished by divider :
3 as well as the reference ~reque~cy are externally supplied.
The sig~al at the output of the phase-lock-loop c~ rcuit, namely : the sig~al at terminal 7 is a signal coupled to the reference frequency supplied at terminal 6.
FIG. 2 shows a block diagram of a second embodiment o~ the present invention~ Again~ oscillator~l generates * ~ ~;
sig~al having a frequency foB ~ 272 x ~ while oscillator 2 ~ur~ishes a si~nal substantially equal to the center frequency ~ :
~OR -282 x f~O The signal havi~g a center ~requency fog is a~llable at ter~inal 7 and that h*~ing a ~requency fo~ is available at termlnal 11~ In thls embodiment the ~requency ;.
divider mean~ comprise third oscillator means, namely an o~cillator 14 ~vhich ~ ished a frequency ~M ~ 277 x ~H and ~ -a n~xing stage 13 .to ~rhose ~irst ~nput is connected the output : ~ ~
o~ oscillator 14 and to whose seco~d input is connected to ' .. ~: :
the output of oscillator 1. The frequency divider ~eans fur~
30 tber co~pr~se a æecond ~lxi~gstage 17. The output o~ oscillator --14 18 applied to the first input o~ mixing stage 17, that of o~cillator 2 to the second lnput. Ihe output ofe&ch mixi~gstage ls ~ ~
the ~u~and dl~erence~lgnal5-of thefrequencyapplled at.the twd ~ ;

,.' , :

.

6~7 1 inputs. Band-pass filters 15 and 18, respectively connected to the outputs of mixing stages 13 and 17, filter the di~fer~
ence s ignals from the output s ignals of the mixing stages.
The outp~t of band-pass f~lters 15 and lB are signals each of wh~ h has a frequency substantially equal to five times -the horizontal line frequency. An additional frequency divider stage lfi is connected at t~ output of band-pass filter 15 and a similar stage 19 is connected to t~ outp~t of band-pass filter 18. Both divider stages divide by a ratio of 1 ~
so th~t the frequency at the output of stages 16 and 19 is substantially equal to the horizsntal line frequency. The reference signal having a frequency equal to the horizontal line frequenoy is applied at a terminal 6 and compared, by means o~ comparators ~ and 20, respectively, to the output of divider stages 16 and 19, respectively. The respective differ- -ence signals are applled through low pass ~ilters 5 and 10, respectively, to oscillators 1 and 2, respectively. The frequency control of the oscillators of ~ourse takes place exactly as in FIG. 1.
It is an advantage of the second embodiment that frequency divider~ having high frequency divider ratios are `
eli~inated. The two signals of center frequencies fog fOR are used to generate two signals each having a ~requency of 6 x fH = 78.125k~z. In order to achive the frequency stab-ility of central frequencies fOB and fOR which is requi~d $or the SECAM system, oscillators 1, 2 and 14 may be stabilized by ;
quartz resonators The ~ost of such quartæ resonators is sub-stantially less than the cost of comparable quartz filters. ~-Band-pass filters 15 and 18 in pre~erred embodiments of the present invention contain active elements. Dividers 16 and 19, in a preferred embodiment of the present invention, are em-bodied in binary counters which are available in integrated circuit ~orm.

_ , ~, . ........... . : . :
~, . . . . . . .

;57 The circuit shown in FIG. 3 ~s a simpllfication of the clrcuit shown in FIG. 2. In particular, a redu~dant channel 1~ ellmi~ated br means appropriate switching circuits, Oscilla tor~ 1 a~d 2 again furnish s~gnals having central frequencies ~0~ a~d fOR ~hich are av~ilable at termlnals 7 and 11 respect~
ively. The s~gnals at the output of oscillators 1 and 2 are each applied to one cantact o~ a ~irst switch 21. It should be noted that these s~itches are of course electronic switches co~trolled by control pulses. S~itch 21 i~ a selector s~itch ~h~ch alternatley furnishes the output of oscillator 1 and oscillator 2 to the input of a ~ix ~g ~tage 22. The other in~
put of mixing stage 22 is again connected to an oscillator 14 ~hich furnishes a frequency equal to fm ~ 277 x fH, The si~-~al at the output o~ mlxing stage 22 is thus (277 + 272~fH. -or (282+277)~ depending upon the posit~on of s~itch 21.
Ba~d-pass filter 23 is used to filter the difference signals fr~m the~e sienal~ so t~ t the output o~ mixing stage 23 is ~:
t~o sig~als each having a ~requenc~ substalltially equal to 5 x f~. These signals are applied to the i~put of frequency :
20 divider 24 ~hich divides in`the ratio 1 ~ 5. The output of :
irequency divider 24 is compaled to the reference signal of horizontal line frequency applied at terminal 6. The co~
parator output is applied by mea~s of a switch 26 alternately, and in synchronis~ wit~ the operatio~ o f switch 219 to os~
cillators 1 and 2. The frequency and phase OI oscillators I and 2 are thus again coupled to the horizontal l~ne fre~
quency. The pulses ccntrolling the switches 21 and 26 applied at a terminal 27 . The oo ntrol is carried out at one-half the horizontal llne frequency. The switches are controlled in :`;
30 such a Dlanner that t~e control signal is applied through ~witch ~6 to oscillator 1 at the same time that the output ~lgnal o~ oscillator 1 is applied to mixing stage 2a through `~

, ....................................... . .

-' ~, ` , . '' ;57 1 switch 21.
In a color televl~ion studio generally m~ e than one SEC~i color carrler coupler is re~uired. Since all of th*se couplers are to operate in synchroni.sffl, tha~: is each is to be coupling the signal fOR ~ fOB at the same t~me, the s~gnal applied at terminal 27 is also used to control similar - s~itches i~ other couplers. This causes all corresponding s~itches 21 and 26 to operate si~ultaneously.
Since in the embodiment shawn in FIG. 3 o~;cillator 10 1 and oscillator 2 are only controlled for time periods last-ing at the most one horizontal line interval, storage elements are provided to store the control sig~al (dlfference signal either with or ~ithout flltering) unt il the next frequency comparison takes place . The t ime re~ui~ed :~ or the output ~requencies at terminals 7 and 11 to reach the desired stabil~zed values both in frequency and in phase ~s there-by substantially decr~ased.
The circult sho~n in FIG. 4 i9 a simplification of the embodiment shown in FIG. 1. A8ain switches are used to ~0 eliDIinate redunda~t components. Specificali.y, one oscillator, o~e phase co~nparator 9 one low pass ~ ilter and osle ~requency . .
dlv~d~r o~ ra~io 1 , 2 are elim~Ilated. I~ the em'bodiment of ` ~ .
FIG. 4, the ~requency at the output s~E oscillator 1/2 may changed by operatioll of a slqitch`28. The freque~cy o~ oscll~
lator 1/2 changes from the irequency f~ to the frequency f~B~
at li~e frequency. This :Is accompli~;hed by a controllab~e -electronic s~itah 28 which receives its switching signals by ;
a control signal o~ one-hal~ thQ horizontal line frequency applied at terminal 27. me slgnal at the output terminal o~
30 the circuit, labelled 7/11, ~ a 8ignal which for alternate llnes has the alternate center frequency fOR or XoB~ m e 81gna1 is applied to two frequency divider~ 29 and 309 re-~pectively dividing by ratios 1 ~ 3 : 47 and 1 : 8 : 17.
A controlled switch 21 connects the output of divider~ 29, _9~

, .-,. ' , ' ` .

1 30, alterDately to the input o~ a divider 32 which is a 1 : 2dlvlder. A~ain, switch 31 ~8 a controlled electron~c switch operating at one-half the horlzontal llne frequency ~n syn-chronlsm w~th swltch 28. Again the output ~ frequency divider 3~ ls applied to a camparator 33 ~hich compares the signal o~ horizontal line frequency applied at terminal 6 to the output of d ivider 32 . The resul tant s ignal ls applied through a lo~v-pass f llter 44 to oscillator 1/2 .
In all og the above embodiments, the difference signals whlch control the frequency of the osclllator may be applied, for example~ to voltage sensitive capacitive diodes ~bose capacitance varies at a functiono~ the voltage applied thereto. The change in capacitance then changes the output ~ :
irequency of the osclllator.
The present invention is not to be limited to the ~ ~`
embodiments shown in FIGSo 1-4 in ma~y respectsO For example, : it is not necessary that the reference signals hav~ a refer~
~ e~ce irequency equal to the horizontal line frequency . The : reXerence frequency may have a frequency which is a predcter~
mined low multiple o~ the horizontal llne frequency. For.
e~ample the embodiment sho~n in FIG. 4 may have a s~gnal ~ur~
:~ nished at the ~erminal 6 which has twice the line ~requency. --~
~nder these circumstances, divider 42 may be dispensed with.
. ..
The systems are also not to be limited bo the partlcular fre~
~ .
quency divider~ shown in the Figures 9 '' , ~;

, , , ~, , , -. , , , ::
, , . , ., ' ~, . . .

Claims (15)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. In a SECAM color television system operating with a predetermined horizontal line frequency, a system for furnish-ing a first and a second color carrier signal locked to the hori-zontal line frequency of the system, the first color carrier sig-nal having a zero-modulation frequency fOR equal to 282 times the horizontal line frequency, the second color carrier signal having a zero-modulation frequency fOB equal to 272 times the horizontal line frequency, comprising, in combination, first oscillator means operative for generating a first oscillator signal constituting the first color carrier signal; second oscil-lator means operative for generating a second oscillator signal constituting the second color carrier signal; means for furnish-ing a reference signal having a reference frequency related to the horizontal line frequency and lower than fOR and fOB; fre-quency divider means connected to receive the first and second color carrier signals and operative for producing first and se-cond frequency-divided signals having frequencies substantially equal to said reference frequency; comparator means connected to receive the reference signal and the first and second frequency-divided signals and operative for comparing the latter against the former to produce first and second difference signals; and means for applying the first and second difference signals to said first and second oscillator means, respectively, for auto-matically adjusting the frequencies of the first and second color carrier signals to lock them on to the horizontal line frequency.

2. A system as set forth in claim 1, wherein said re-ference frequency is equal to the horizontal line frequency.

3. A system as set forth in claim 2, wherein said fre-quency divider means comprises means operative for dividing the frequency of the first color carrier signal by 282 and that of the second color carrier signal by 272, wherein said comparator means comprises a first phase comparator having a first input connected to receive the first frequency-divided signal and having a second input, and a second phase comparator having a first input connect-ed to receive the second frequency-divided signal and having a second input, the second inputs of the first and second compara-tors being connected to both receive the same reference signal, and wherein said means for applying said first and second dif-ference signals to said first and second oscillator means com-prises a first and a second low-pass filter respectively connect-ed between the outputs of the first and second phase comparators and the first and second oscillator means.

4. A system as set forth in claim 3, wherein said fre-quency divider means comprise separate first and second frequency divider means.

5. A system as set forth in claim 4, wherein said first and second frequency divider means comprise binary frequency dividers.

6. A system as set forth in claim 4, wherein said first frequency divider means comprises a first divider for divid-ing by a factor of two, a second divider connected to said first divider for dividing by a factor of three, and a third divider connected to said second divider for dividing by a factor of forty-seven.

7. A system as set forth in claim 4, wherein said second frequency divider means comprise a first, second, third and fourth frequency divider connected in cascade, each for divid-ing by a factor of two, and a fifth frequency divider connected to said fourth frequency divider for dividing by a factor of seventeen.

8. A system as set forth in claim 3, wherein said first oscillator means, said first comparator and said first low pass filter are constituted by an integrated circuit having an input for receiving said reference signal and an output for furnishing a controlled oscillator output signal, said controlled oscillator output signal constituting said first color carrier signal.

9. A system as set forth in claim 1, wherein said fre-quency divider means comprise third oscillator means for furnish-ing a third oscillator signal having a frequency equal to 277 times the horizontal line frequency and a first and second mixing stage each having a first input for receiving said third oscillator signal, a second input for receiving, respectively, said first and second oscillator output signals, and an output for furnish-ing, respectively, said first and second frequency-divided sig-nal each having a frequency substantially equal to 5 times the horizontal line frequency, and wherein said comparator means com-prise first and second phase comparator means for, respectively, comparing said first and second frequency-divided signals to said reference signal.

10. A system as set forth in claim 9, further compris-ing a first and second band-pass filter connected to the output of said first and second mixing stage, and a first and second 1 : 5 frequency divider connected to the output of said first and second band-pass filter, respectively, for furnishing, re-spectively, a first and second frequency-divided signal having a frequency substantially equal to said horizontal line frequency to said first and second comparator means, respectively.

11. A system as set forth in claim 10, wherein said first and second band-pass filter each comprise an active filter.

12. A system as set forth in claim 1, wherein said frequency divider means comprise third oscillator means for furnishing a third oscillator signal having a frequency equal to 277 times the horizontal line frequency, mixing means having a first and second input and an output, for furnishing a mixer output signal having a frequency corresponding to the difference between the frequencies of signals applied at said first and se-cond inputs at said mixer output, connecting means for connecting said first input of said mixing means to said third oscillator means and said second input alternately to said first and second oscillator means, respectively, a band-pass filter connected to said mixer output, and 1 : 5 frequency divider means connected to the output of said pass filter means, whereby said first and second frequency divided signals are furnished alternately at the output of said 1 : 5 frequency divider means; wherein said means for furnishing a reference signal comprise means for furnish-ing a reference signal having a reference frequency equal to said predetermined horizontal line frequency; wherein said comparator means comprise a single phase comparator for comparing said re-ference signal to the outputs of said 1 : 5 frequency divider means; and wherein said means for applying said first and second difference signal to said oscillator means comprise switching means operated in synchronism with said connecting means for applying said output of said phase comparator means alternately to said first and second oscillator means.

13. A system as set forth in claim 12, further com-prising control means for controlling the operation of said connecting means and said switching means to operate at a fre-quency of one-half the horizontal line frequency.

14. A system as set forth in claim 1, wherein said first and second oscillator means comprise a shared oscillator, first and second frequency changing means for changing the fre-quency of said oscillator when connected thereto, and switch means for alternately connecting said first and second frequency changing means to said oscillator î wherein said frequency divider means comprise a first frequency divider having a 1 : 3 : 47 fre-quency divider ratio and a second frequency divider having a 1 : 8 : 17 frequency divider ratio connected to said oscillator means, a third frequency divider having a 1 : 2 frequency divider ratio, additional switch means for alternately connecting the output of said first and of said second frequency divider to the input of said third frequency divider, and means for operating said additional switch means in synchronism with said first switch means; wherein said comparator means comprise a single phase com-parator having a first input connected to said means for furnish-ing a reference signal, a second input connected to the output of said third frequency divider and a phase comparator output;
and wherein said means for applying said first and second dif-ference signal to said oscillator means comprise a low pass filter interconnected between said phase comparator and said oscillator means.

15. A system as set forth in claim 14, further compris-ing means for furnishing a control signal for controlling the operation of said first and said additional switch means, said control signal having a frequency equal to one-half the horizon-tal line frequency.