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Патент USA US3078349

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Feb. 19,, 1963
KAZUMI TAKEUCHI
SYSTEM FOR DEMQDULATING CHROMINANCE SIGNAL
" Filed March 16. 1960
3,073,339
COLOR TELEVISION’
-
2 SheefLQ-S?bat 1"
FE. J.
LUMINANCE
SECOND DETECTOR
SIG. AMP.) LUMNANCESIG.
ADDER\ AMPLITUDE DET.
3
5
3
l2
iDEMODULATION
l6
OUTPUT
1
m9 ' Lj 9
6
l9
'1 lo
M
,7 __[ DEMODULTATION
H
[5
6I
LINE AND FRAME SYNC.
OSCILLATORS—\ 4
7
,
gmmmus
SUBCARRIER osc.
l 1l
>
-
OUTPU
I
,ADDER AMPLITUDE DET.
H515;
ADDER\
Z5
BAND PASS AMP.
20 2
>4 Z4
Z/
AMPLITUQEDET.
Z7
3/
25' '
Z?
33
_
4 DEMODULATION '
OUTPUT- w
ADDER
34
Z DEMODULATION.
OUTPUT
SYNCHRDNDUS
PHASE
SUBCARRlER DSC. SHIFTER
ADDER
AMPLlTUDE DET..
\
Feb. 19, 1963 -
KAZUMI TAKEUCHI
3,078,339‘
SYSTEM ‘FOR DEMODULATING CHROMINANCE SIGNAL IN COLOR TELEVISION
Filed March 16.. 1960
2 Sheets-Sheet 2
H5151
3,0783%
United
Patented Feb. 19, E963
2
--—-->
FIG. 3, 0X and OZ represent respectively special phases
3,973,339
of the chrominance subcarrier references to demodulate
the chrominance signal and also a set of corresponding
chrominance subcarrier references is generated by phase
shift circuit 7 of the subcarrier, and the signal represented
SYSTEM FUR DEMQDULATHNG CHROMENANSE
SEGNAL EN C(PLQR TELlEVlSlQN
Kmumi Taheuchi, Harajuizu-machi, Tozulralru, Yoko
harna tflity, Japan, assignor to Hitachi Limited, Chi
yoda-ku, Tokyo, Japan
——_—>
by 'OX is supplied to the addition circuits 8, 9, and the
signal represented by OZ is supplied to the addition cir
Filed Mar. 16, 1960, Ser. J. *0. 15,349
Claims priority, application Japan dune 13, 1959
Z Qlaizns. (Cl. 178--5.4)
———->
10
—>
cuits 19, 11 respectively. 0C represents a transmitted
carrier chrominance signal which may be obtained at the
output terminal of the band pass ampli?er together with
This invention relates to a system for demodulating
chrominance signal in color television.
The object of this invention is to provide a color tele
vision receiver which has simple construction and can be 15 the phase reversed 00’.
built at a lower cost.
0C and OC' have the same
magnitude and 0C is supplied to addition circuits 8, 10,
In heretofore known color television receivers, a color
and 0C’ is supplied to h, 11 respectively. The signal OP
subcarrier signal separated out of the composite video
signals is supplied to two synchronous detectors and
which
is the vector sum of 0C and OX is obtained at
further two chrominance subcarrier reference synchron 20
the
output
terminal of the addition circuit 8 and the signal
ously oscillated by a separately transmitted color burst is
-—>
-—>
—->
applied to the synchronous detectors with each phase as
OQ which is the vector sum of OC’ and OX is obtained at
special phases to be demodulated to obtain color signals
the output terminal of the addition circuit 9. Since the
or color difference signals. According to such known
change of the hue to be transmitted is transmitted as the‘.
-—>
systems at least two vacuum valves are necessary for syn
chronous detection. Such vacuum valves can be dispensed
with by this invention and they are substituted with
25
several resistance or reactance circuits and an amplitude
detector, thereby simplifying the construction and reducing
the cost.
This invention will now be explained with reference to
an embodiment as shown in the accompanying drawings,
in which
FIGS. 1 and 2 are block diagrams respectively illustrat
ing a part of the circuit system of the color television 35
receiver embodying demodulating system of chrominance
signals in color television according to this invention,
FIG. 3 is a vector diagram for illustrating the principle
of operation of an embodiment of this invention as shown
in FIG. 1, and
FIG. 4 is a similar vector diagram relating to another
-——->
change of the phase of carrier chrominance signal, 00
——->
and 0C’ revolve around the point 0 as the hue changes.
At this time, P and Q revolve at the opposite positions
on the circumference of circle A having X as a center.
The diameter PQ of the circle A is equal to OC’ and is
proportional to the degree of color saturation. Similarly,
the signal OR which is the vector sum of OC and OZ is
obtained at the output terminal of the addition circuit It}
__>
-—>
—-->
and the signal OS which is the vector sum of 0C’ and OZ
is obtained at the output terminal of the addition circuit
11. The relation between these signals and circle B is’
similar to the relation between the signals and circle A
-——>
as above mentioned. If the phase angle between 0C and
embodiment as shown in FIG. 2.
‘ Referring to FIG. 1, 1 represents a second detector of
OX be 01 and that between OC and OZ be 02, then the
the color television receiver, 2 designates the circuit for
following equations will be established:
amplifying the luminance signal only and transmitting it,
and 3 represents the output of the luminance signal. The
luminance signal is supplied to the jointly connected
special electrode of a three electron gun type colour tele
vision display tube or to matrix circuits. 4 represents hori
zontal and vertical synchronous oscillation circuits, the
output of which is connected to the deflecting yoke of the
picture tube, 5 represents a band pass ampli?er for the
chrominance signal component and 6 represents synchron
ous oscillation circuits of the reference subcarrier, to which
the color burst is supplied from band pass ampli?er 5, and
on the other hand, fly-back pulses are supplied thereto 55
Amplitude detectors i2, 13, 14 and 15 are all square
from horizontal and vertical synchronous oscillation cir
detectors as above described and the output signals ampli
cuit 4. 7 represents a phase shift circuit of the reference
tude-detected in these detectors can be expressed by the
subcarrier which is used for regulating the reference sub
Equation 1, 2, 3 or 4 respectively. If the addition circuit
carrier generated by the synchronous oscillation circuit 6
16 is operated to take the difference between signals of the
of the reference subcarrier to a special phase necessary
Equation 1 and Equation 2, then the output as expressed
for demodulating chrominance signals. 8, 9, l0 and 11
by the following Formula 5 is obtained as the output 18:
represent an addition circuit respectively for adding the
carrier chrominance signals and the chrominance sub
carrier references, which may be a resistance circuit or a
reactance circuit. 12, 13, 14 and 15 represent an ampli
tude detector respectively, which has preferably square
curve detection characteristics, thoughit is not necessary
to limit it. 156 and 17 represent addition circuits respec
41521 H31 cos a
('5)
Similarly, if the addition circuit 17 is operated to take
the difference of the signals expressed by the Equations 3
and 4, then the output expressed by the following For
mula 6 is obtained as the output It‘).
tively. 1S and 19 represent respectively color signals or
70
color difference signals which have been demodulated.
4621 [0m cos a,
(s)
The operation of the circuit arrangement shown in FIG.
Formulae 5 and 6 are proportional to the orthogonal
1 will be explained by the vector diagrams as shown in
3,078,839
It
3
projection of the carrier chrominance signal correspond
and OZ be 02, then the Formulae l, 2, 3 and 4 are estab
lished. The signals which are amplitude-detected at
square curve characteristics detectors 27, 28, 29 and 3%
become like the Formulae 1, 2, 3 and 4 respectively. If
ing to the special phases OX and OZ to be demodulated
respectively so that these become required demodulated
signals which are same as the signals demodulated by a
conventional process using synchronous detectors.
the addition circuit 31 is operated to take the dilference
between signals obtained by the Formulae l and 2, the
output represented by Formula 5 is obtained at the termi
nal 33. Similarly, the output represented by Formula 6
The invention will be explained with reference to an
other embodiment in the following:
Referring to FIG. 2, 29 represents a band pass ampli?er
of chrominance signal component, and '21 represents syn
is obtained at the output terminal 34 of addition circuit
chronous oscillation circuits of the reference subcarrier 10 32. These are same as the demodulated signals using the
signal, wherein color burst is derived from the band pass
synchronous detectors same as in the former example. In
ampli?er 20 for chrominance signal component and the
the foregoing description, the properties of detectors were
reference subcarrier phase-controlled by the color burst is
assumed to be square curve characteristics, but if there
generated. 22 represents phase shift circuit for the refer
are provided the following conditions:
ence subcarrier whichis used for regulating the reference
carrier wave generated in the synchronous oscillation cir
cuit 21 of the reference subc'arrier to special phases neces
———>
—>
sary for demodulating chrominance signals. Different
from the above described example, the output signals of
this phase shifting circuit 22 generates, besides a, set of
]OZ|>>IOC[
Then the properties of detector may be generally n
power property. Under the above conditions, the‘ Equa
‘necessary special phase signals, another set of signals hav
tion 1 becomes
ing phase difference of 180° from the ‘said set. 23, 24-,
25 and 26 represent respectively the circuit for adding
carrier chrominance signals and chrominance subcarrier
references which may be either a resistance circuit or
react'ance circuit. 27, 28, 29 and 30 represent amplitude
detectors preferably of those having square curve detection
{0X1
IOX I
Accordingly, the signal obtained through the detector
having n-p'ower detection characteristics becomes as the
following Formula 8 by approximate calculation by omit
properties similar tothose in the former example. 31
and 32 represent addition circuit. 33 and 34 represent
color signals or color difference signals‘ demodulated re
spectively. The operation of the circuit will be explained
_
-——>
--—>
(8)
with reference to FIG. 4, wherein OX and OZ represent
special phases of the carrier chrominance signal to be
demodulated and also a set of chrominance subcarrier 35
.———>
-—-->
Similarly, the detected signal obtained by the Formula 2
becomes as the following Formula 9
references corresponding to the phases. OX’ and OZ’ rep
resent another set of chrominance subcarrier references
having phase difference of 180° to the said ?rst set of the
chrominance subcarrier reference, while OX=OX’ and
Similarly, the detected signal obtained by the Formula
OZ=OZ’. Two sets of these chrominance subcarrier ref
erences can be obtained from the phase shifting circuit 22.
3 becomes as the following Formula 10
--—>
0C represents transmitted carrier chrominance signals
which may be obtained by the band pass ampli?er 20 of
the carrier chrominance signal and it is supplied to addi
(10)
Similarly, the detected signal obtained by the Formula
——->
tion circuits 23, 24, 25 and 26 in parallel. OX is supplied
4 becomes as the following Formula ll
-——>
to addition circuit 23, and OX’ is supplied to addition
(11)
circuit 24. OZ is supplied to addition circuit 25 and OZ’
to addition circuit 26. OF which is the vector sum of 00
—--»->
and OX is obtained at the output terminal of the addition 55
Each signal of the above Formulae 8, 9, l0 and 11 is
obtained by amplitude detectors i2, 13, 14 and 15 as
circuit 23, while 0Q which is the vector sum of 0C and
shown in FIG. 1 respectively. In the second example,
-——>
such signal is obtained from detectors 27, 28, '29 and 30
OX’ is obtained at the output terminal of addition circuit
as shown in FIG. 2 respectively. If the difference signal
24 and 00 rotates aroundthe point 0 as the transmitted 60 of the Formulae 8 and 9 is taken out then the signals of
——>
,
--—>
hue varies. Then P and Q rotate on the circumferences
the following Formula 12 is taken from the output ter
minals of the addition circuit 16 or 31 and if the differ
ence of Formulae 10 and 11 is taken out, then the signal
The radii of circles A and A’ are equal to OC and propor
of the following Formula 13 is obtained from the output
—>
65 terminal of addition circuit 17 or 32.
tional to the degree of colour saturation. ‘Similarly, OR
of circles A and A’ having center at X and X’ respectively.
——>
_—>
which is the vector sum of 0C and OZ is obtained at the
'—-9
output terminal of addition circuit 25, and OS which is
-——->
—->
_
the vector sum of OC and OZ’ is obtained at the out
put terminal of addition circuit 26. The relation between
these signals and circles B and B’ is similar to that be
tween above mentioned circles A and A’. If the phase
-—->
—-'—>
-—-—>
angle between 0C and OX be 01 and that between 0C
70
Formulae l2 and 13 are same as the signals detected
by a conventional synchronous detectors as above de
scribed.
The addition circuit is so arranged that after
the signals are added they are detected and then their
di?erence is taken, yet it may be so arranged that sub
8,078,389
6
carrier wave signals to be added may be applied to the
anode and ‘cathode of the detector respectively and then
the difference of signals detected can be obtained by the
current ?owing through the common impedance.
As above described, color signal demodulators of a
known color television is a synchronous demodulator so
that it has been necessary to use a vacuum tube having
more than two elements, but in the present invention the
minance signal according to claim 1, wherein said carrier
demodulator may consist of several resistance or reac
said phases of X and Z, the phase of said signal X being
opposite to the phase of said signal X’, the phase of said
signal Z being opposite to the phase of said signal Z’, said
four adding means adding individually said carrier chro
tance addition circuits and four amplitude detectors
(crystal detectors) so that the construction can be made
very simple and inexpensive.
chrominance signal source supplies a carrier chrominance
signal C to four adders, said chrominance subcarrier ref
erence signal sources supplying four reference signs X,
X’, Z and Z’ having phases locked to the color signal,
said signals X and Z each having a phase adapted to re—
produce a predetermined demodulation output with syn
chronous demodulations being individually effected on
minance signal and one of said chrominance subcarrier
What I claim is:
reference signals and supplying vector sums X +C,
l. A system for demodulating a color television chro
minance signal, said system comprising a carrier chromi 15 X ’+C, Z+C and Z’+C’, said system further comprising
four means to detect individually amplitudes of said four
nance signal source supplying two carrier chrominance
signals C and C’ having opposite phases, chrominance
vector sums, means to subtract said detected output
subcarrier reference signal sources supplying signals X
(X ’+C ) from said detected output (X +C ) , means to sub
and Z phases locked to the color signal, means to add one
tract said detected output (Z'+C) from said detected out
of said carrier chrominance signals and one of said chro 20 put (Z +C ), and means to use said two subtracted output
signals as two color difference signals.
minance subcarrier reference signals and then to supply
vector sums of X+C, X+C’, Z+C and Z+C’, means to
References Cited in the ?le of this patent
detect amplitudes of said four vector sums individually,
means to subtract said detected output (X +C’) from said
UNITED STATES PATENTS
detected output (X +C), means to subtract said detected 25
output (Z+C’) from said detected output (Z+C), and
means to use the two subtracted output signals as two
color signals.
2‘ A system for demodulating a color television chro
2,858,428
Torre _______________ .._ Oct. 28, 1958
2,899,492
2,935,686
Cooperman et al ________ __ Aug. 11, 1959
Kerns et al ____________ .._. May 3, 1960
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