Note: Descriptions are shown in the official language in which they were submitted.
109~0738
BACKGROUND OF THE INVENTION:
.
The present invention relates to generally a color
television receiver and more particularly a video amplifier -~
therefor combined with a matrix circuit for combining the lumi-
nance signal with the color difference signals.
In general, the Y or luminance signal of the color
television or colorplexed video signal is transmitted with a
wide band while the chrominance signal, with a narrow band. The
luminance signal and the carrier chrominance signal are recover-
; 10 ed by the luminance and chrominance signal processing circuits,
respectively, in the television receiver, and are combined in
a matrix circuit to derive the primary color signals which
control the intensities of the beam currents in a picture tube
; for the reproduction of the picture in color.
In the prior art video amplifier combined with thematrix circuit of the type described above, the color differ-
ence signal amplifier comprises a common-emitter transistor with
¦ the feedback and collector output capacitances of the order of
1.5 to 2.5 PF. The high-frequency component of the luminance
signal applied to the collector is negatively fed back so that
~ the high-frequency components of the primary color signal de-
.'! rived from the collector are lost. That is, the color differ-
ence signal amplifier must be so designed that even though its
function is to amplify the color difference signal transmitted
with a narrow band, it must minimize the loss of the high-
frequency components of the luminance signal. To overcome this
` problem, there has~been proposed to connect a Darlington circuit
consisting of transistors to the base of the transistor in the
color difference signal amplifier. In other words, a low-output
impédance conversion circuit is connected to the color difference
signal amplifier so as to minimize the effects due to the col-
lector feedback capacitance of the transistor in the color
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; difference signal amplifier. However the above circuit arrange-
ment is very complex. Moreover the emitter of the transistor
in the color difference signal amplifier is grounded so that
the DC operating point drifts due to the ambient temperature
variation. Therefore it is not desirable to directly couple
the output of the video amplifier to the picture tube.
Especially the -G primary color signal changes in the direction
opposite to that of the other -R and -B primary color signals
due to the temperature drift of an inverter so that the white
or color balance in the picture tube is adversely affected.
SUMMARY OF THE INVENTION:
One of the objects of the present invention is there-
fore to provide a video amplifier for a color television re-
ceiver which may eliminate an impedance conversion circuit used
in the conventional video amplifiers and in which the primary
color signals with the excellent qualities may be recovered from
the combination of the luminance signal with the color differ-
ence signal in a matrix circuit which is very simple in con-
struction.
Another object of the present invention is to provide
a video amplifier which may minimize the loss of the high-
, frequency components of the luminance signal in the matrix
circuit.
, A further object of the present invention is to pro-
vide a video amplifier which may minimize the adverse effects
due to the temperature drift upon the transistors making up the
matrix circuits, thereby ensuring the stable operation.
To attain the above and other objects, according to
-i the present invention, the luminance signal is applied to the
collector circuit of a differential amplifier comprising a first
transistor and a second transistor with their emitters connect-
ed together; the color difference signal is applied to the base
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of the first transistor; and the primary color signal is derived
across a load resistor inserted in the collector circuit.
Therefore, the stable operation and hence the excellent repro-
duction of the picture in color may be ensured.
More particularly, there is provided a video amplifier
characterized by the provision of a differential amplifier com-
prising a first transistor and a second transistor with their
emitters connected together, the luminance signal being applied
to the collector circuit of said differential amplifier, the
color difference signal being applied to the base circuit
; of said first transistor, and the primary color signal being
derived from a load circuit coupled to said collector circuit.
The present invention will become more apparent from
the following description of the preferred embodiments thereof
taken in conjunction with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING:
i
Fig. 1 is a block diagram of one example of the prior
art video amplifiers for color television receivers;
~ Fig. 2 is a block diagram of a first embodiment of the
,,~
' 20 present invention; and
.1
1 Figs.3, 4, 5, and 6 are schematic circuit diagrams
,~. . . ~
1 of second, third, fourth and fifth embodi~ents of the pre-
. .,
;~1 sent invention, respectively.
DESCRIPTION OF THE PREFERRED EMBODI~NTS:
Prior Art, Fig. 1
Prior to the description of the preferred embodiments
,, .
of the present invention, one example of the prior art video
amplifiers having a transistorized matrix circuit will be des-
cribed briefly in order to more specifically point out the de-
~;i
fects or problems encountered in the prior art video amplifiers.
Referring to Fig. 1, to terminals Tl and T2 are appliedthe R-Y and B-Y signals, respectively, which are demodulated
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~0407;18
by a chrominance signal processing circuit. The R-Y signal
applied to the input terminal Tl is converted into the low out-
put impedance signal in an impedance converter comprising a Dar-
lington pair consisting of transistors Ql and Q2 and a resistor
l, and thereafter amplified by a transistor Q3 in the next
stage. Since the DC voltage containing the luminance signal
is applied from a transistor Q4 to the collector of the tran-
sistor Q3, the red primary color signal -R is derived from a
terminal T4, that is the collector of the transistor Q3 because
the -(R-Y) signal is combined with the luminance signal -Y. In
like manner, the B - Y signal applied to the terminal T2 is com-
bined with the luminance signal in the transistor Q4 so that
the blue primary color signal -B is derived from a terminal T5.
~ The G-Y color-difference signal is derived from a
; matrix circuit consisting of resistors 8, 9, and lO to which
are applied the R-Y signal from the emitter of the transistor
Q2 and the B-Y signal from the emitter of a transistor Q6. The
polarity of the G-Y signal is opposite to that of the R-Y and
B-Y signals, that is -(G-Y). Therefore, the polarity of the
-(G-Y) signal is inverted by a transistor Q8' and thereafter,
converted into the low output impedance signal in a circuit
comprising a Darlington pair consisting of transistors Qg and
Qlo and an emitter resistor 13. The output of the second
Darlington pair is amplified by a transistor Qll in the next
~; stage so that the green primary color signal -G is derived from
the collector of the transistor Qll' that is a terminal T6.
As described above, the prior-art video amplifier
requires two Darlington configuration impedance conversion cir-
cuits in order to minimize the decrease the high frequency
components of the luminance signal in the primary color output
signals. For instance, in order to simplify the circuit, it
is preferable to increase the value of the collector resistor
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3 of the transistor Q3, which is used for the amplification of
the R-Y signal and is also an element in a matrix circuit for
combining the amplified R-Y signal with the luminance signal
-Y, so that the voltage amplification factor may be increased.
However the feedback capacitance between the base and
; collector and the collector output capacitance of the transis-
tors used in such circuit are of the order of 1.5 to 2.5 PF so
that the high-frequency components of the color difference and
luminance signals are negatively fed back due to the feedback
capacitance. As a result, the high-frequency components of the
primary color signal derived from the collector of the transis-
tor Q3 are lost. In order to minimize the loss of the high-
frequency components due to the feedback capacitance, the
j Darlington pair Ql and Q2 is provided so that the color differ-
ence signal with a low output impedance may be applied to the
j base of the transistor Q3. In this case, the collector output
;~ capacitance becomes 3 to 5 PF because the collector output capa-
i citance is added to the feedback capacitance. Such arrangement
has a distinct defect that the value of the collector load re-
sistor 2 cannot be increased because the high-frequency compo-
nent loss must be minimized in the color difference signal
amplifier Q3 which amplifies the color difference signal with
a narrow band.
Moreover, the loss of the high-frequency components
of the primary color signal cannot be avoided because of the
- load resistor 3 and the collector output capacitance of the
transistor Q3. Same is true for the circuits for recovering
the -G and -B primary color signals. The circuit for recover-
ing the -G primary color signal must include an inverter, that
is Q8.
Still referring to Fig. 1, the difference color sig-
nal amplifiers are of the common-emitter type so that the
iO40738
excursion of the DC operating point tends to occur due to the
ambient temperature variation. Therefore, it is undesirable to
provide a directly-coupled stage between the video amplifier and
a picture tube. Especially the -G primary color signal changes
in the direction opposite to that of the other R and B color
signals due to the temperature drift of the inverter so that
the white or color balance in the picture tube is adversely
affected.
As described hereinbefore, the prior art video ampli-
fier has the distinct defects (1) that it requires the low
output impedance conversion circuits in order to minimize the
effects caused by the collector feedback capacitance of the
transistors used for the amplification of the color difference
signals; (2) that the high-frequency components of the luminance
signal are adversely affected by the collector output capaci-
tance and the load resistor, thus resulting in the unsatis-
factory kinescope reproduction of the picture in color; (3)
that the white or color balance of the kinescope is adversely
affected by the temperature drift or variation; and ~4) that
an inverter for inverting the polarity of the G-Y signal must
be provided. In view of the above, the present invention was
made to overcome the above and other defects and problems en-
countered in the prior art video amplifiers.
The Invention
First Embodiment, Fig. 2
. ,
Referring to Fig. 2, the first embodiment of the
. ~
present invention will be described. The R-Y signal is applied
to the input terminal Tl of a diferential amplifier comprising
transistors Q12 and Q13' emitter resistors 16 and 17, bias
resistors 18 and 19 for giving the negative bias to the emit-
ters of the transistors Q12 and Q13' respectively, and a col-
lector load resistor 20 for the transistor Q13 Since the base
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of the transistor Q13 is grounded, the loss of the high-
frequency components of the luminance signal due to the collec-
tor feedback capacitance of the transistor Q13 may be minimized.
The loss of the high-frequency components of the luminance sig-
nal due to the collector load resistor 20 and the collector
output capacitance of the transistor Q13 may be also compen-
sated. The collector of the transistor Q12' which has the
collector feedback capacitance, is biased by the DC containing
the luminance signal so that the high-frequency components of -`
the luminance signal are fed back from the collector to the base
of the transistor Q12 The transistor Q13 in the next stage
has its base grounded so that the amplified and in-phase high-
frequency components of the luminance signal are derived from
the collector of the transistor Q13 The high-frequency com-
ponents of the luminance signal thus derived may effectively
; compensate the high-frequency components of the luminance
attenuated by the load resistor 20 and the collector output
capacitance of the transistor Q13 The above described high-
frequency compensation makes it possible to increase the value
of the load resistor of the -(R-Y) color difference signal
amplification transistor Q13 Since this compensation is
attained by the fact that the color difference signal demodula-
tor coupled to the base of the transistor Q12 has an output
impedance, the impedance conversion circuit of the type des-
cribed with reference to Fig. 1 may be eliminated. The -(R-Y)
color difference signal amplifier comprises the differential
amplifier circuit having the self-balancing function, and makes
up the matrix circuit in which the -Y luminance signal is com-
bined with the -(R-Y) color difference signal. Thus the -R
primary color signal which is derived from the output terminal
T4, may be applied through a directly-coupled stage to the
picture tube because the excursion of the DC operating point
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due to the ambient temperature variation may be prevented.
In like manner, the -(B-Y) signal applied to the in-
put terminal T2 is amplified and combined with the -Y luminance
signal. That is, the -(B-Y) signal amplifier comprises a dif-
ferential amplifier consisting of transistors Q14 and Q15' emit-
ter resistors 21 and 22, and a collector load resistor 23 of
the transistor Q15 The amplified -(B-Y) color difference
signal is combined with the -Y luminance signal so that the
-B primary color signal may be derived from the terminal T5.
Resistors 24 and 25 are inserted in order to give the negative
bias to the emitters of the transistors Q14 and Q15 The mode
of operation of the -(B-Y) color difference signal amplifier
is substantially similar to that of the -(R-Y) signal amplifier
described hereinbefore so that no further description shall
be made in this specification.
The G-Y color difference signal may be recovered by
combining the (R-Y) and (B-Y) signals in the conventional man-
ner in a matrix circuit, which is shown as comprising three re-
sistors 26, 27, and 28. The output or (G-Y) color difference
signal from the matrix circuit is applied to the base of a
transistor Q16 which makes up a differential amplifier with
another transistor Q17 The negative bias is applied to the
emitters of the transistors Q16 and Q17 through resistors 29,
30, 31, and 32. The G-Y color difference signal applied to the
base of the transistor Q16 has its polarity reversed as is clear
from the well known matrix equation
; a(R-Y) + b(B-Y) = - (G-Y)
where a and b are coefficients. According to the present in-
- vention the emitter of the transistor Q16 in the G-Y color
difference signal amplifier is grounded, and the polarity in-
verted -(G-Y) signal is applied to the collector of the tran-
sistor Q16 DC potential containing the luminance signal is
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applied from the emitter of the transistor Q4 through a collector
load resistor 33 to the collector of the transistor Q16 There-
fore the -Y luminance signal is combined with the G-Y color
difference signal so that the -G primary color signal is derived
from the collector of the transistor Q16' that is, the terminal
T6. The loss of the high-frequency components of the luminance
signal may be effectively compensated by the transistor Q17'
a capacitor Cl and a resistor 34.
The transistor Q16 in the G-Y color difference sig-
nal amplifier is driven in the common-emitter mode so that the
; output is derived from its collector. The base of the trans-
istor Q16 is connected to the matrix resistors 26, 27, and 28
so that its impedance is of the order of a few kilo ohms.
:
Therefore the high-frequency components of the luminance signal
in the DC collector bias are fed back to the base due to the
feedback capacitance between the collector and base of the
transistor Q16 so that the amplified and phase-inverted high-
.
frequency components of the luminance signal are negatively
j fed back to the collector.
Since the base of the transistor Q17 is grounded
~, through the resistor 34, the high-frequency components of the
luminance signal in the collector bias is fed back to the base
of the transistor Q17 Since the transistors Q16 and Q17 make
up the differential amplifier, the high-frequency components
of the luminan¢e signal fed back to their bases are in-phase
and equal in amplitude. Thus, it is apparent that there exists
no negative feedback which would result in the amplified and
phase-inverted high-frequency components of the luminance sig-
nal at the collector output terminal because the high-frequency
components are fed back to the base. Thus, the loss of the
high-frequency components of the luminance signal due to the
feedback capacitance between the collector and base of the
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104073B
output transistor may be compensated.
The loss of the high-frequency components of the
luminance signal due to the collector output capacitance and
collector load resistor 33 of the transistor Q16 may be effect-
ively compensated by the feedback of the high-frequency compo-
nents of the luminance signal through the capacitor Ql inter-
connected between the collector and base of the transistor Q17
Like the -(R-Y) and,-(B-Y) color difference signal amplifiers,
the G-Y color difference signal amplifier comprises the dif-
ferential amplifier having the self-balancing function so that
the G-Y signal is combined with the luminance signal to produce
the -G primary color signal at the terminal T6. The -G primary
~, color signal will not cause the excursion of the DC operating
"i point due to the ambient temperature variation. Therefore the
,,,, directly-coupled stage to the kinescope may be simplified in
;'' construction.
Second Embodiment, Fig. 3
'`' The second embodiment to be described with reference
to Fig. 3 is substantially similar in,construction to the first
;, 20 embodiment shown in Fig. 2 except that a parallel circuit con-
,.
', sisting of a capacitor 35 and a resistor 36 is interconnected
, .
between the ground and the base of one transistor Q13 (or Qls)
which makes up the differential amplifier with the other tran-
sistor Q12 (or Q14) When the value of the resistor 36 is
suitably selected so that the base bias voltages of the tran-
12 ( Q14) and Q13 (or Q15) may be made equal to each
other, the drift due to the ambient temperature variation may
be satisfactorily compensated.
Third Embodiment, Fig. 4
The third embodiment to be described hereinafter with
reference to Fig. 4 is substantially similar in construction
to the second embodiment except that a parallel circuit con-
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sisting of a capacitor 37 and a resistor 38 is interconnected
between the collectors of the transistors Q12 and Q13 (or Q14
and Q15) The collector currents of the transistors Q12 and
Q13 (or Q14 and Q15) are made substantially equal by suitably
selecting the value of the resistor 38.
Fourth Embodiment, Fig. 5
;
The fourth embodiment shown in Fig. 5 is substantially
similar in construction to the first embodiment shown in Fig. 2
except that a resistor 39 is connected in series to the base
of the transistor Q12 (or Q14) so that the feedback from the
collector to the base of the transistor Q12 (or Q14) may be
increased. Therefore the loss of the high-frequency components
~, in the luminance signal may be well compensated.
Fifth Embodiment. Fig. 6
' The fifth embodiment shown in Fig. 6 is the combina-
... .
tion of the second, third and fourth embodiments shown in Figs.
3, 4, and 5, respectively, That is, the parallel circuit con-
sisting of the resistor 35 and the capacitor 36 is intercon-
nected between ground and the base of the transistor Q12 (or
Qls), another parallel circuit consisting of the capacitor 37
and the resistor 38 is placed between the collectors of the
transistors Q12 and Q13 (or Q14 and Qls),
is connected in series to the base of the transistor Q12 (or
Q14) The adverse effects caused by the ambient temperature
variation may be further minimized and the loss of the high-
frequency components of the luminance signal may be further
i well compensated.
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