Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
The invention relates to a transmission system
for a colour television signal, in particular in a system
for recording on and reproducing from a record medium,
in which method a transmission signal is generated having
a first signal component comprising ]uminance information,
a second signal component comprising a first colour carrier
wave modulated with a first colour information component
and a third signal component comprising a second colour
carrier wave modulated with a second colour information
component, which second and third signal components are
arranged to occupy separate frequency bands.
Such a transmission system, which is Eor
example known rom Netherlands Patent Application
No. 6,603,605 of P. Thomson published June 20, 1966,
has the advantage that it is highly insensitive to timing
errors introduced during transmission. This is of particular
interest when a colour television signal is recorded on and
reproduced from a record carrier, for example a magnetic tape
or an optically readable video disk. In said systems timing
errors are inter alia introduced by speed variations
of the record carrier and in the case of the video dlsk
also by the presence of the eccentricity. When in such
recording systems the chrominance signal is recorded
in known manner as a quadrature signal, i.e. on two 90
~ '.
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. ~
~56~7
phase-shifted carrier waves of the same frequency, which
are amplitude modulated with two colour signals, said
timing errors will show up in the reproduced chrominance
signal as a hue error, which is very disturbing.
In a transmission system of the kind mentioned
in the preamble said timing errors have a far less
disturbing effect because the signals which are modulated
on separate carrier waves, in particular frequency-
modulated carrier waves, are substantially less sensitive
to said timing errors than a quadrature-modulated signal
as mentioned previously. ``~
However, a drawback of a system as mentioned
in the preamble is that it is very sensitive to variations
in the transfer function of the system. A variation
in the transfer characteristic, which may result in the
second and third signal component being no longer subject
to the same transfer function? causes a hue error in
the reproduced chrominance signal, which as previously
stated, is highly disturbing.
It is an object of the inventlon to proyide a
transmission system of the type mentioned in the pre-
amble, which mitigates said problem whilst the said ad-
vantages are maintained. For this, the invention is
characterized in that the first and second colour information
components are constituted by a first and the second colour
signal in a line~sequentially interchanged fashion. ~
The step according to the invention first of -
all ensures that during the reproduction from a record
-3- ~-
~ ,
~ 5S~7
~¦ PIrN 7~9
3.2.197~
carrier, which is provided with a colour television sig-
nal which is thus composed, an effective use is made of
the averaging of the colour over two lines which is ef-
fected in a colour television receiv~r adapted for re-
i 5 producing a colour t01evision signal in accordance
~ with the PA~ standard. Owing to s~id averaging a
:~i
possible hue error arising from differences in the
~¦~ transfer function for the second and third signal
¦ components is autornaticall~ compensated for. The same
¦ 10 applies to differences in noise and bandwidth of thetransmission channels for said second and third sig-
nal components. Moreover, the same record carrier
j can also be played via a playing apparatus adapted
to the SECAM colour television system without said
differences in the transfer function giving rise to
`~ hue errors.
Moreover, the system according to the invention
is highly suited to be employed with pre recorded record
carriers, i. R . reco:rd carriers which have already been
__
provided ~ith a programtne by the manufacturer. In this
respect, the video disk, which at present is in the
focus of interest, lS an obvious application. Of course,
it is of advantage when such a pre-record0d record car-
rier can be distributed as widely as possible. In Europe
this presents the problem that t~o different colour te-
levision standard~ are ~eing used, namely PAL and SECAM,
.~ ' ` . .
~ - 4 -
, ~
;~ . .
5 6 ~7 P~ 79~?~
. .3-2-1976
,
¦ 80 that a pre-recorded record carrier which is speci-
¦ fically adapted to either of said standards cannot be
1 played without any further p:rovisions in those areas
¦ where the other standard is used. The transmisslon sys-
tem descri~ed is universal in this respect, because the
second and third signal component may contain two ele-
mentary colour signals, from which with the aid of cod-
ing circuits in the playing equipment a colour tele-
: vision signal in accordance with the P~L or SECAM
~ 10 standard can easily be obtained. This means, that for
¦ the entire PAL-S~CAM territory it is sufficient to use
onQo and the same record carrier without bhis Xaving any
: : significant, particularly price-increasing consequences
~ with respect to the playing equipment.
.
Finally, it has been Pound that the transmis-
¦ sion system according to the invention is particularly
¦ ~ advantageous. in the case of said video disks, namely~3
¦ . in the case of slow-motion or quick-motion reproduc-
¦ tion of a recorded programme, which will be explained
! 20 hereinafter,
-. The invention will now be described with
reference to the Figures, in which
1 Fig 1 shows a frequency spectrum of the
l transmitted television signal in a transmission sys
, Z5 tem accordlng to the invention,
.~ Fig. 2 shows a diagram in explanation of
~! said spectrum,
,~ : ,
~ -' ' , ' , , .
.,.,~ ,
i
~ , . , . . ; . : , :. ~
7 ~ 56~7 3.2.1976
Fig. 3 shows a first embodiment of a recording
~ or transmission apparatus,
¦ Fig. 4 shows a first embodiment of a reproduc-
¦ ing or receiving apparatus for use in a system according
to -the invention,
Figs. 5 and 6 show -two diagrams to explain
~ .
the operation,
Figs. 7 and 8 sho~ two alternatlve embodiments
of the recording or transmission apparatus for use in
a system according to the inventiont
Fig. 9 shows a diagram to explain the opera-
tion thereof,
Flg. 10~hows an alternative embodiment of the
reproducing or receiving apparatus for~use in a system
according to the invention~ whilst
Fig. 11 shows a diagram pertaining thereto and
Fig. 12 schematically shows an embodiment of a
lo~ic ci~cuit applied on th2 reproducing apparatus
according to the invention.
Figure 1, by way of example, shows a frèquency
spectrum of a colour television signal as may be trans-
mitted in accordance with the transmission system ac-
~ ~ cording to the invention. The luminance signal is
!
j frequency modula~ed on a carrier wave ~y and
covers a frequency sweep of fs (synchronizing pulsej
- 6.7 MHz to fw (pea~ white) = 8~4 MHz. It is assumed
that the first slgnal componont E , which in addition
'
; - 6 -
.
~ ~56~7 `~
to said frequency sweep also contains the first-order
sidebands, covers a bandwidth of 4.2 - 11.4 MHz. The
frequency spectrum furthermore contains a second slg-
nal component El, which as a modulation of the first
colour carrier wave Fl contains a first colour signal, `
and a third signal component E2, which as a modulation
of a second colour carrier wave F2 contains a second
- colour signal. Said second and third signal components
occupy separate frequency bands~ for example frequency
bands of 1.2 MHz aroand the two carrler frequencies
of 1.8 and 3.2 MHz respec~ively. For completeness a
fourth signal component Eg is shownj which consists
of a carrier wave F which is frequency modulated wlth
the audlo signal.
First of all, it is to be noted that the in-
vention is by no means limited to the positions of
the various signal components within the available
bandwidth selected in Figure 1. As far as the principle
of the invention is concerned the location of said signal
components within the frequency spectrum is of no
importance at all. As an example, the second and third ;
signal components may alternatively be situated within the
frequency band covered by the first signal component, as is
for example described in Netherlands Patent Specification
106~695 of N.V. Philips published March 15, 1963, or one of
said signal components may be situated beIo~ and the other
above the frequency band covered by said first signa] ~
component. -~'
': "
.~ '':
" , . . ....
6~7
PHN 79~
3-2-1~76
Furthermore, it is to b~ noted that the method
of modulation of the first and second oolour carrier F1
and F2 by the two colour signa:Ls is not an essentlal
step of the invention. For exarnple in thls respect an
amplitude modulation or a frequency modulation may be
~ considered. For other reasons, _ ter alia the greater
,~ .
noise immunity, said colour carrier waves are
pref`erabIy frequency-modulated, which is the reason
why further in the description only this frequency-
modulation will be discussed.
Finally, it is to be noted that the compo-
sition of the colour signals is not of` direct import-
ance, although the use of colour difference sig~nal (R-Y)
, .
and (B-Y) is most advantageous. Therefore, said t~o
~ : ~
colour difference sign~s (R-Y) and (B-Y) will be
: .
selected hereinafter as modulating signals for the
two colour carrier waves F1 and E2
In accordance with the invention the two
signal component~ E1 and E2 no longer continuously
oontain the same colour signal, but ~ese two
colour signals are added to the two colour carrier waves
F1 and F2 as a modulation signal in a line-sequentially
alternating fashion. In Fig. 2 *his is schematically
represented for (R-Y) and (B-Y) colour signals,
which Eigure shows as a function of` the line number Ln
which colour signal is included in the second signal
3~ component E1 and which colour signal in the third sig-
:!:
_ 8 -
5~ P~IN 7996
~ - 3.2.1976
'
nal component E2. Thls shows that everey alternate line
the signal component E1 comprises the -two colour signals
R - Y) and (B Y) and the signal component ~2 a~ter-
nately contains the same colour signals but in phase
opposition.
~ igure 3 shows a f`irst embodiment of an ap-
paratus, with which such a colour television signal
can be obtained at the transmitter side or in the re-
.~ .
cording equipment for a record carrie3r. Said apparatus
first of all comprises a transcod0r 2, which splitssa
co1lour television signal which is applied to a ter-
minal 1 into a luminance signal Y, and two colour
difference signals (R - Y) and (B - Y), The circuit
arrangement of said transcoder is of oourse det0rmlned
by the composition of the colour -television slgnal ap-
plied to the terminal 1. If said colour television sig-
.
- nal is a signal composed in accordance with a standard
(for example PAL) said transcoder 2 may for example
correspond to the decoding device employed in
receivers for the relevant standard colour television
signal. However, any known transcoder which is capable
of supplying the three slgnals (R - Y), (B - Y) and Y `~-
- may be used.
3 The ex-tracted luminance signal Y at ter-
minal 6 is frequency modulated in an ~M modulator 14,
resulting in the ~irst;;signal compcnent Ey. The two
!~, oolour components (R - Y) and ~B - Y) ar0 applied to
g _
.. . ., . .
lU56~
PI-IN 799
21.5.75
: . .
~: the two input terminals 1~ and 5 of a commutator 30 Said
, .
commu-tator 3 comprises a dual interlocked switch, ~lich
~ can assume two positions, viz. a first posi-tion in w~h
I a connection is established between the input terminal
~ii 5 4 and an output terminal 10 on the one hand, and an
input terminal 5 and an outpu-t terminal 1l on the
~' other hand, and a second position in which a connection
~¦ is established between the input terminal 4 and the
output termi.nal 11 on the one hand and the input -ter-
minal 5 and the output -terminal 10 on the other hancl.
Said switch, whi.ch in practice will of course take the
form of any known electronic switch, is contro:~ed by
~¦ a control signal at a control terminaL 8 of the commu-
¦ . tator 30 With the aid of a detector 9 said control sig-
':
nal i9 derived from the horizontal synchronizing pulses
¦ in the television signal, which are .for example taken
from.an output terminal 7 of the transcoder 2, and which
control signal is constituted by a symmetrical square-
wa~e signal of half the line frequency. This ensures
tha-t the commutator 3 is controllecl in such a way
. that at its output terminals 10 and 11 the colour
: ~ .
signals (R - Y) and (B - Y) are available in phase
opposition every altcrnate line, in accordanGe with
the diagram of Fig. 2. The signal at terminal 10 is
applied to a frequency modulator 12, in which said
alternating colour signal is modulated on a carrier
wave F1, resulting in the.second signal component E1.
, ~ .
,
~r . ~ 10
.
~1 .
S~ 7
The signal at terminal 11 is applied to a frequency
modulator 13, in which said alternating colour signal
is modulated on a carrier wave F2, resulting in the
third signal component E2. Said second and third sig~
nal component El and E2 are summed with the aid of
a summation device 15.
Said sum signal (El + E2~ should then more-
over be combined with the first signal component E
and, as the case may be, with a sound signal E , which
is added to a carrier wave F of for example 0.5 M~lz as
a frequency modulation, which signal is applied to a ~
terminal 17. A simple method to achieve this is described ~;
in United States Patent No. 3,893~163 of United States Philips
Corp. issued July 1, 1975. In that case the signal components
(El + E2) and E of comparatively low frequency are added to
the first signal component E , which has finitely steep edges,
and the sum signal (E + El + E2 + E ) is applied to
a limiter circuit 18. Thus~ at the output terminal 19
is obtained a squarewave signal whose frequency
contains the luminance information and in which the
colour sum signal (El + E2) and the sound signal Eg
are contained as a pulse-width modulation, which
signal is particularly suited to serve as a recording
signal for an optically readable video disk.
Figure 4 shows an embodiment of the receiving
or reproducing equipment for a colour television signal
which is thus transmitted or recorded. From the
--11~
- ~as~
;
colour television signal applied to an input terminal 21, which signal is for
example obkained from a video disk with the aid of an optical reading system,
the first signal component Ey is extracted with the aid of a high-pass
filter 24, from which the luminance signal Y is demodulated with the aid of
an FM demodulator 27. The second and third signal components El and E2 are
extracted with the aid of two band-pass filters 22 and 23, after which the
colour signals are recovered from said signal components with the aid of two
FM demodulators 25 and 26. Said colour signals are applied to the two input
terminals 29 and 30 of a commutator 28. Said commutator is of the same
design as the commutator 3 at the transmitter side, i.e. having two input ~ `
terminals 29 and 3Q and two output terminals 31 and 32 which are alternately
interconnected as a function of a control signal at a control terminal 33.
Said control terminal 33 receives a control signal Erom a logic circuit 34.
Said logic circuit 34 has three input terminals 35, 36, 37, of which terminal
35 can receive a control signal from a command device 38, terminal 37 a
control signal from an identification circuit 39, and terminal 36 a control
signal from a detector 40 via a switch 51.
The function of the command device 38 and the identification
circuit 39 will be described in more detail hereinafter. First of all, it
will be indicated how the original continuous colour signal can be recovered
with the aid of the commutator 28. ~or this purpose, the circuit 51 must be
in the position P ~PAL) in which position the horizontal synchronizing
pulses which are detected from the luminance signal Y by the detector 40
reach the input terminal 36 of the logic circuit 34. In response to this
logic circuit 34 supplies a symmetrical square wave signal of half the line
frequency to the control terminal 33 of the commutator 28, so that the
position of the commutator switch is changed every line. The result of this
is shown in the block diagram of Figure 5.
Said Figure 5 indicates for three consecutive lines n, n-l-l, n+2
of a television picture which colour signal is available at the inputs 29 and
- 12 -
~ ~,
~ 56~7
30 and the outputs 31 and 32 of the commutator 28 during ~he relevant lines.
The indexes near said colour information signals indicate via which signal
components El or E2 said colour information has been transmitted. It is
assumed that the input 29 of the commutator 2S receives the colour signal,
which has been transmitted as a modulation of ~he first colour carrier Fl ;
and the input 30 receives the colour signal which has been transmitted as a ;
modulation of the second colour carrier F2. The two inputs 29 and 30 con~
sequently receive the ~R - Y~ and ~B - Y~ colour signal every alternate `
line, but in mutuaI phase opposition.
If it is now assumed that during the line n the commutator 28 ~ `~
establishes the connection pattern represented by the continuous lines, the
output 31 receives the (R Y)l colour signal from input 2~ during said line -~
and the output 32 the ~B -~ Y~2 colour signal from input 30. D~lring the next
line the commutator establishes the connection pattern represented by the
dashed lines and output 31 consequently recel~es the ~R - Y)2 colour signal
from input 30 and output 32 the ~B - Y~l colour signal from input 29.
Consequently, the output 31 o~ the commutator 28 continuously supplies the
~R - Y) colour signal, said colour signal being alternately obtained ~rom
FM demodulator 25 and 26 line-sequentially. In a similar way the output 38 ~;~
now continuously supplies the ~B - Y) signal.
In order to recover a standard colour signal in accordance with
the PAL standard from said two colour difference signals ~ - Y) and ~B - Y~
the two colour signals must be quadrature-modulated in known manner on a
4.43 MHz carrier wave. For this purpose, it may be desirable to add burst
keying pulses to the t~o colour signals in two adder circuits 41 and 42.
Said burst keying pulses may be derived from the horizontal synchronizing
pulses detected by the detector 40 and serve for obtaining in known manner,
the desired burst on the backporch of the horizontal flyback period in the
case of modulation of the colour signals on the 4.43 ~Hz carrier. When said
burst keying impulses have already been added to the colour signal at the
~ 13 -
transmitter side, said adder circuits 41 and 42 may be dispensed with, which
in the Figure is indicated by the dashed connections between the outputs 31
and 32 o~ the commutator 28 and the A~-modulators 43 and 44. The desirabil-
ity of generating said burst keying impulses in the receiving equipment
depends on possible disturbances in the transmitted burst keying impulses.
In this respect it is to be noted that in a PAL receiver also a certain
compensation is obtained in respect of possible disturbances in said burst
keying impulses because of the averaging over two lines.
The colour signal ~B - Y~ provided with burst ke~ing pulses is
applied to a first amplitude modulator 43 which as carrier wave receives a
4.43 MHz signal of fixed phase (- sin) from an oscillator 45. The colour
signal ~R - Y) provided with burst keying pulses is applied to an amplitude
modulator 4~, which also receives a 4.43 Ml-lz carrier wave signal from said
oscillator 45, but which carrier wave is 90 phase-shifted relative to the
carrier wave which is applied to the modulator 44 and which moreover exhibits
a 180 phase alternation every other line (~ cos). By adding the thus
obtained two modulated colour signals in an adding circuit 47 a chrominance
signal is obtained which complies Wit}l the PAL standard and which is quad-
rature modulated. Said chrominance signal is added to the demodulated
luminance signal Y in an adding circuit 48, so that at an output terminal 49
a PAL standard colour television signal becomes available, which may be
applied to a standard PAL-colour television receiver.
In order to illustrate the effect of the step according to the
invention reference is made again to ~igure 5 and the vector diagram shown
in Figure 6. The column PAL-ID in Figure 5 indicates which PAL phase is
added to the (R - Y) signal of the relevant lîne in the AM modulator 44,
whilst the column PAL-chroma indicates the ultimate vectorial composition of
the PAL chrominance signal of the relevant line.
If it is now assumed that owing to whatever cause the transfer
characteristic of the second signal component El has a higher gain factor
~356~7
; '
than the transfer characteristic of the third signal component E2, the colour
signals ~B - Y)l and (R - Y)l will always have too high a value compared with
the colour signals (B - Y)2 and ~R - Y)2. The effect of said difference in
gain factor will be described with reference to Figure 6.
For this it is assumed that the colour signal which is transmitted
via the third signal component E2 has the correct value. During the line n
the ~B - Y)2 colour signal consequently has the desired value (B-Y)nC, the
upper index indicating the relevant line The ~R - Y)l colour signal,
however, is too great during said line _, i.e. greater than the desired signal
(R - YjnC. The result of this is that instead of the correct colour vector
~.
Ccn _ (B - Y) c + ~R - Y)nC during said line n the colour vector
cn = (B ~ Y) nc + (R _ y)nl is obtained. Said colour vector cr~ e~hibits a ;~
phase error ~ relative to the desired vector Cnc, which means that there will
be a hue error, which is very disturbing.
In accordance with the invention, however, the colour vector Cn+l
during the line n+l is composed of the (B _ y)ln 1 colour signal and (R _ y)2n 1 r
colour signal, the ~R - Y)2 signal now having the correct value (R - Y)nC 1,
which for simplicity is assumed to be equal to (R _ Y)m~ and the (B - Y)l
signal being too great relative to the desired value by the same factor, as ~;
was the case with the ~R - Y)l signal during the line n. The colour vector
.
n 1 which corresponds to said line n+l consequently consists of Cn 1 _
~B _ y)ln 1 _ ~R - Y)nC 1, the -sign being the result of the negative PAL phase
(- cos) which prevails during said line n + 1. In a PAL receiver, however,
, :
the vectorial sum of the two colour vectors of two consecutive lines is now
determined whilstpreviously the vector Cn I which corresponds to the
negative PAL-phase (- cos) is reflected relative to the (B - Y) axis, which
sum vector is the ultimately reproduced colour signal. The vector Cn 1 is
consequently first reflected relative to the (B - Y) axis, resulting in a
CP n 1, which vector is then vectorially added to the vector C n which yields
the vector C n + CP n 1. The Figure shows that the phase of the said sum ~;~
-15-
`~
~ S~ 7
vector is entirely correct compared with the desired colour vector Cc, so
that no hue error will result. The only error which remains is an error in
the colour saturation, as said sum vector is greater than twice the desired
colour vector 2Cc, but this is considerably less disturbing than a hue error.
The transmission system according to the invention moreover has
additional advantages, which will be discussed in more detail with reference
to the previously described embodiment of Figure 4. It has already been
; stated that the transmission system according to the invention is parti-
cularly advantageous for pre-recorded record carriers, because in the
reproducing apparatus a colour television signal suitable for a PAL receiver
or for a SECAM receiver can be obtained in a very simple manner. The `
generation of a PAL colour television signal has already been described
hereinbefore, so that this will not be discussed any further.
To obtain a SECAM colour signal it suffices to set the switch
51 to the position S. A SECA~ colour signal comprises the (R - Y) and
~B - Y) colour signal alternately from line to line. When switch 51 is set
to the position S, the logic circuit 34 will no longer receive any horizontal
synchronizing pulses from the detector 40, so that the control terminal 33
of the commutator 2~ will not receive a control signal and the commutator
switch remains in a fixed position. This means that the two outputs 31 and
32 are continuously connected to a fixed input 29 and 30. Thus, the ~R - Y) ;~
and (B - Y) colour signals will occur line-sequentially at each of said
two outputs. Consequently, a line-sequential colour signal FSEcAM can be
taken from one of said outputs~ for example 31, which signal is available
at an output terminal 5Q. To derive a complete SECAM colour television signal
from this, said colour signal ~SECA~ should merely be modulated on the
standard colour carriers and subsequently be added to the luminance signal
Y. In order to simplify the block diagram this obvious step has not been
further elaborated.
A further advantage of the transmission system according to the
- 16 -
i: , .,.. ;,, : :
~ 156~7
invention is obtained ~hen a disc is used as a record carrler, although it
is also applicable to the use of a record carrier in the form of a tape.
~or further details on the use of an optically ~coded video disk as a record
carrier, reference is made to United Sta~es Patent Specification 3,85~,015
~PHN.6225). Generally, the video information is recorded on such a video ~;
disk in a spiral track, in such a manner that per revolution of said disk "
exac~ly one full television picture is recorded. In order to realize a
stationary picture with the aid of such a video dislc, it is sufficient to
; move the scanning spot with which the informatlon is read one track pitch
back after every revolution of said disk, so that each time the same tele-
vision picture is reproduced. rn the case of reproduction of a signal record- ~ ,
ed in accordance with the PA~ colour television standard this gives rise to a
problem owing to the alternating phase of the PA~ colour signal, see United
States Patent No. 3,974,519 of United States Philips Corp. issued August 10,
1976. Since a television picture in accordance with the PAL standard contains
625 lines, the first and last line of a PAL colour television signal always
have the same PAL phase. However, this means that when realizing a stationary
picture the line-se~uential alternation of said PAL phase is always interrupt-
ed at the beginning of the picture, so that the reproduced colour signal may ~;
be disturbed.
When using the transmission system according to the invention
this presents no problem, as the alternatlng PAL phase is not added to the
colour signal until in the read apparatus, namely during the modulation of
the (R - Y) colour signal on the standard chrominance carrier (4.43 MHz~ with
alternating phase (+ cos) in the modulator 44. However, in order continuous-
ly to maintain the ~R - Y) colour signal at the output 31 of the commutator
28 in the case of a stationary picture, the commutator switch should perform
an extra switching cycle upon every revolution of the video disk. The first
and the last line of one and the same recorded television picture contain
the same colour signal, for example ~R - Y), because of the odd number of
- 17 -
516~7
:: :
lines, so that without additional switching the output 31 ~ould contain the
(R - Y) colour signal during one picture period, the ~B - Y) colour signal
during the next picture period etc. Because of the additional change-over
of the commutator switch at picture frequency, this is prevented.
Said additional change-over can be accomplished very simply with
the aid of the command device 38. Said command device 38 will already be
provided in the reading equipment and control the desired movements of the
scanning spot for realizing of said stationary picture. Consequently, it is
very simple to cause said command device 38 to apply an additional pulse to
the input 35 of the logic circuit 34 during each return of the scanning spot,
so that said logic circuit 34 will supply an additional changing pulse to
the commutator 28. It will be evident that everything that has been said in ;,
respect of stationary pictures also applies to other devlating reproducing
speeds, such as slow-motion or reverse-motion pictures.
~igure 4 finally shows an identificatlon circuit 39. Said identi-
' fication circuit 39 serves to ascertain in the case of PAL reproduction
; whether output 31 of the commutator actually carries the (R - Y~ colour signal
and output 32 the (B - Y) colour signal. Should these be interchanged owing
to an incorrect alternation phase of the commutator switch, said identifica-
tion circuit 39 with the aid of an identification signal which is included
in the video signal, for example burst keying pulses, supplies an additional
pulse to an lnput 37 of the logic circuit 34, so that the commutator switch
performs an additional change-over. ~hen the transmitted burst keying pulses
are used as identification signal, and if the disturbance-free burst keying
; pulses are to be added, erase circuits should be included before the adding
circuits 41 and 42 in order to erase the transmitted burst keying pulses.
Figures 7 and 8 show two alternative embodiments of an apparatus
with which a PAL-standard colour television signal can be transformed into a
colour television signal as transmitted with the system according to the
invention. ~;
- 18 _
'~,
56~17
` ' ''-`'
For the apparatus of;~igure 7 it has: been assumed that the
chrominance component of the colour television signal according to the PAI.- ~ `
standard is applied to an input terminal 51. Said chrominance signal conse-
quently contains a quadrature-modulated chrofninance signal on a 4.43 MHz
colour carrier. In order to derive the two colour signals (R - Y) and ~B - Y)
from this, an oscillator 52 is provided which supplies two carrier waves,
derived from the colour burst, ~ith a frequenc~ of 4.43 MHz, but which are ~`
mutually 90 phase shifted ~sin and cos). One of said carrier ~aves is ;
applied to a phase inverter 53 ~hich line-sequentially changes the phase of
the carrier wa~e by 180~. Said phase alternating carrier wave (+ cos) and
the fixed carrier wave ~sin) from the oscillator 52 are applied to two inputs
54a and 54b of a commutator 54, whose outputs 54c and 54d are respectively
connected to two amplitude demodulators 56 and 57 (inputs 56b and 57b respec- `
tively), to which moreover the original chrominance signal from terminal 51
is applied ~inputs 56a and 57a respectively~. In a similar way to the phase
inverter 53, said commutator 54 receives a control signal at its control input
55 from a detector 62, which detects the line pulses from the luminance in-
formation of the PAL colour television signal applied to a terminal 69, so
that both the phase inverter and the commutator are switched line-sequentially,
whilst by operation of said detector 62 it is assured that the phase inverter
53 assumes the correct position in accordance with the PAI. phase of the
applied chrominance signal.
If it is assumed that the commutator 54 is in the position re~
presented by the continuous line~ the ~B - Y) colour signal is derived at the
; output of the AM demodulator 56, and ~ia a lo~-pass filter 58 becomes ava
able at a terminal 60. Simultaneously, at the output of AM demodulator 57
the ~R - Y) colour signal is obtained~ ~hich signal becomes available at a
terminal 61 via a low-pass filter 59. During the next line via the commutator
54 the cos-signal of the 4.43 ~Hz carrier is applied to the ~U~ demodulator 56,
so that at terminal 60 the ~R - Y~ colour signal is o~tained, whilst at the
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,
~56( 17
same time the ~B ~ Y) colour signal becomes available at terminal 61. Thus,
at the two terminals 60 and 61 the two desired colour signals ~R - Y) and
(B - Y) become alternately available line-sequentially, to be transmitted via
separate fre~uency bands by modulating them on two different colour carriers
Fl and F2.
` Figure~8 shows a second embodiment of an apparatus for obtaining
the desired colour signals from a PAL-standard chrominance signal for the
~ transmission system according to the invention~ Correspondlng elements are
;; denoted by the same reference numerals as in Figure 7. The PAL-chrominance `"
. 10 signal is again applied to an input term mal 51, which is now connected to a
delay line 63, which dela~s said chrominance signal by one line period. The
delayed chrominance signal is applied both directly and via an inverter 64
: : :
; to the two inputs 65a and 65b of a commutator 65, which at its control input
66 receives a symmetrical squarewave signal which is supplied by the line ~ ~`
pulse detector 62, so that said commutator is changed over line-sequentially.
ln order to explain the operation of said apparatus reference is
made to the block diagram of ~igure 9. Said diagram shows the signals which
,~ appear at different points of the apparatus for five consecutive lines L ~
The PAL chrominance signal at terminal 51 i5 represented as U ~ V and U - V
alternately so as to denote the alternating PAL phase, U being the (B - Y)
colour signal modulated on 4.43 MHz, and ~ being the (R - Y) colour signal
modulated on 4.43 ~Hz. The indexes now denote the line during which said
chrominance signal is applied. The output signals A and B of the commutator
65 will contain the chrominance signal which has been delayed by one line
period, the polarity changing every line by operation of the inverter 64. The
output signal A is added to the undelayed chr~minance signal in an adding
circuit 67, resulting in the chrominance signal indicated in column 67, and
the signal B is added to said undelayed chrominance signal in an adding cir-
cuit 68, resulting in the signal indicated in column 68, in which it is
assumed that the colour components of the two consecutive lines differ only
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~ 56C~7 ~
slightly. ~rom these tNo columns 67 and 68 it can be seen that at the outputs
of the two adding circuits 67 and 68 onl~ one colour component is present.
Apart from the commutator 65, said circuit is in fact identical to the cir-
cuit generally used in PAL receivers for averaging phase errors.
~ The chrominance signals supplied by the adding circuits 67 and
i 68 are applied to the AM demodulators 56 and 57 respectively, which also
respectively receive the carrier Naves C and D, which with the aid of a phase
- inverter 53 and commutator 54 are derived from an oscillator 52 in an
identical manner to that shown in Figure 7. This results in the colour
signals indicated in the columns 60 and 61 at the terminals 60 and 61. It
can be seen that the desired colour sequence is obtained again at the two
terminals. The difference with the device shown in Figure 7 is that the
colour signal which becomes ava:ilable during a specific line, for example
(B - Y)l2 is the average of the colour signals (B - Y)l and (B - Y)2, i.e.
each time the two colour signals of two consecutive lines. Of course, this
is the result of the use of the delay line 63. The advantage of the device
of Figure 8 compared with that of ~igure 7 is the requirements to be imposed
on tbe AM demodulators 56 and 57 will be less stringent.
Figure 10 shoNs an alternative embodiment of a reproducing appara-
tus for the transmission system according to the invention, the signals which
appear bein~ shown in the diagram of ~igure 11. Corresponding elements are
denoted by the same reference numerals as in ~lgure 4. The colour television
signal which has been read is again divided into the signal components El,
E2 and Ey with the aid of band-pass filters 22 and 23 and a low-pass filter
24. Said signal components are demodulated with the aid of FM demodulators
25, 26 and 27. At the outputs of the two ~M demodulators 25 and 26 the line-
sequentially alternating colour signals (R - Y), ~B - Y) etc. are obtained
again. To these two colour signals the burst keying pulses are now added in
the adding circuits 41 and 42. As to the alternating colour signals ~R - Y)
3~ and ~B - Y~ ~eying pulses of opposite polarity should be applied a commutator
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~o~
71 is required, whose two outputs are connected to the adding circuits 41
and 42 and whose two inputs are connected to the line pulse detector 40,
which supplies both keying pulses of positive polarity and keying pulses of
negative polzrity which are locked to the detected line impulse in the
luminance signal y to said commutator 71. Said commutator 71 is controlled
via a control input 72 by the logic circuit 34, which in its turn receives
a control signal from the detector 40. Thus, the correct burst-keying pulses
; are always added to the demodulated colour signals. These two colour signals
provided with keying pulses, at the outputs of the two adding circuits 41 and
42 ~columns 41 and 42 in ~igure 11~ are then applied to the two AM modulators
43 and 44 (inputs 43a and 44a~. To these two AM modulators are applied two
carrier waves E and F with a frequency of 4.43 MHz, whose phase is line
sequentially switched (inputs 43b and 44b). This is again effected with the
aid of a 4.~3 M~lz oscillator 54 w~lich supplles two 90 phase-shifted carrier
waves (sin and cos), whilst one of said carriers moreover changes polarity
line-sequentially (l cost~. These two carrier wave signals are applied to
a commutator 73, which at its control input 74 receives a control signal from
the logic circuit 34 and thus changes over line-sequentially. As a result,
the colour signals ~R - Y) and (B - Y) are always modulated on a carrier wave
of the correct phase. At the output 43c and 44c of the two AM modulators
line-sequentially alternating colour signals are still obtained, but they
are now modulated on carrier waves with a frequency of 4.43 ~ and are there-
fore represented by U and Y in analogy with ~igure 9. By adding said two
colour signals in an adding circuit 47 a chrominance signal (column 47 in
Figure 11~ is obtained which fully complies with the PAL standard and which
when added to the luminance signal y in adding circuit 48 yields a complete
PAL colour television signal YpAL at the output terminal 40.
Finally, Figure 12 schematically shows an embodiment of the logic
circuit 34 together ~ith the identification circuit 39. The identification
circuit 39 for example receives the colour signal from output 32 of the
35~7
commutator 28 (see F~gure 4). Said signal is applied to a switching tran-
sistor 80, which at its control electrode 81 receives such pulses, derived
from the horizontal synchroni~ing pulses, that said switching transistor is
; conducting during ~he time intervals in which the colour signal at output
32 contains the transmitted burst keying pulses. Ihese transmitted burst
keying pulses are applied to a capacitance 82. As is known, the keying pulses
which are added to the (R ~ Y) colour signal are positive and the keying
pulses which are added to the ~B - Y~ colour signal are nsgative. Depending
on the colour signal which is present at the output 32 the voltage across the
capacitance 82 will consequently be positive or negative. Said voltage is
transferred via an amplifier 83 and an integrator 8~ with an integra~ion time,
of, for example, 200 line periods~ to an input of a comparator 85, whose
second input is connected to earth potential. Said comparator for example
has a preferred posltion which corresponds to a negative input signal, which
in its turn corresponds to the presence of the ~R - Y) colour signal at the
output 32 of the commutator 28. ~lo~ever, if the switching phase of said
commutator 28 should not be correct and the (B - Y) colour signalshould con-
sequently appear at the output 32, the signal which is applied to the com-
parator 85 becomes positive, sO that said comparator changes over. With the
aid of a monostable multivibrator 86 a suitable pulse is then applied to the
terminal 37 of the logic circuit 34.
Sald logic circuit 3~ furthermore comprises a terminal 35, which
is connected to the command device 38. The two terminals 35 and 37, via a
differentiating network which consists of the capacitances 87 and 88 and the
; common resistor 89, are coupled to an amplifier 90, which supplies a pulse
of the desired duration as soon as one of said terminals 35 and 37 receives
a pulse. The logic circuit 34 further comprises a D flip-flop 91, whose set
input S is connected to the aTnplifier 90. The outputs Q and Q of said 0
flip-flop are connected to the ~ and K inputs of a ~K flip-flop 92. The Q
output of said JK flip-flop is connected to an input of an AND-gate 94 and
,,
' ' ' ' . , 1
~l~S6~;D7
the Q-output to an input of a NAND~gate 93. At their output inputs these
two gates 93 and 94 receive the line-synchronizing pulse train supplied by
; the detector 4Q, which is also applied to the T input of the JK flip-flop 92.
; The output of the gate 93 is connected to the reset input R o~ the D flip-
flop 91 and the output of the gate 94 to the T input of a JK flip-flop 95.
The J and K inputs of said JK flip-flop 95 are connected to a common terminal
96, whilst the signals at either of the t~o outputs Q and Q may ~e used as
switching signals for the commutator 28.
The operation of the circuit is as follows. By feedback via the
gate 93 to the reset input R of the D flip-flop 91 a stable state is obtained
in which a logic 1 appears at the Q output and a logic 0 at the Q output
of flip-flop 91. As a result, a logic 1 and 0 are also present at the Q and
Q output respectively of the JK Elip-flop 92. The AND-gate 9~ in this state
consequently transfers the llne-synchronizing pulses train from detector 40
to the T input of the JK flip-flop 95. Should the colour signal which is
applied to the reproducing apparatus need to be transformed into a standard
PAL signal, a logic 1 is applied to terminal 96, so that as a result of the
line-synchronizing pulse train at the T input, the logic level of the two
outputs Q and Q changes line-sequentially, so that the position of the
commutator is also switched line-sequentially.
When subsequently one of the terminals 35 or 37 receives a
pulse, the set input S of the D flip-flop receives a pulse and the state of
said D flip-flop changes, i.e. the Q output supplies a logic 0 and the Q
output a logic 1. As these two outputs are connected to J and K inputs of the
JK flip-flop, the state of said JK flip-flop also changes upon the next line
synchronizing pulse at the T ~nput. The Q output then supplies a logic 0 to
the AND-gate 94, so that the second, subsequent line synchronizing pulse from
detector 40 is not transferred to the R input of the JK flip-flop 95 and said
Elip-flop does not switch over its output signals. As the Q output of the
JK flip-flop 9Z supplies a logic 1 to the NAND-gate 93, said second line
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56 ~7
synchronizing pulse is applied to the reset input R of the D flip-flop, so
that after said second line synchronizing pulse the stable state is restored.
A pulse at one of the terminals 35 and 37 thus eventually ensures
that the linc-sequentially alternating control signals which becomes available
at the outputs of the J~ flip-flop 95 for the commutator 28 are maintained
in one state durin~ two line periods, so that said commutator 28 remains in
the same state during these t~o line periods, which yields the desired phase
inversion of the commutation. It ~ollows that the phase inversion of the
commutation mentioned in the introduction of the specification is to be
understood to include both the omission of a change-over prescribed by the
line-synchronizing pulse train and the performance of an extra commutation,
for example during the vertical flyback period.
It is obvious that the embodiment of the logic circuit is by no
means limited to the embodiment shown. Various modifications are also
conceivable in respect o~ the modulation method in which the three signal
components are recorded on a record carrier. Obviously, said modulation
method is not essential ~or the principle of the invention. For the purpose
of illustration reference is made to the United States Patent No. 3,963,862
issued June 15, 1976 and United States Patent No. 3,962,720 issued June 8,
lg76, both of United States Philips Corp.
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