Note: Descriptions are shown in the official language in which they were submitted.
~08Z3~ RC~ 70,33~
This invention relates to a kinescope pincushion
distortion correction circuit.
It is known in the art that side or East-West
pincushion distortion of the raster on a kinescope such as
utilized in a television receiver may be substantially ~ ;
eliminated by modulating the horizontal rate deflection
current amplitude through the horizontal deflection coils by
a substantially parabolic current component at a vertical
scanning rate. Generally the desired modulation has been
accomplished by passive circuits in which a control or
primary winding of a saturable reactor or transformer is
energized by vertical rate energy and a secondary winding is
placed in circuit with the horizontal deflection winding.
The horizontal deflection current amplitude is modulated
by the vertical deflection current such that the raster width
is reduced at the top and bottom of the raster.
Another known arrangement for side pincushion -~
distortion correction involves a capacitor coupled in
20 parallel with the vertical de~lection winding. As is '
disclosed in copending Canadian application Serial No.
244,531 filed on January 29, 1976 for Peter E. ~aferl,
the capacitor is charged by energy from the horizontal
retrace pulse under the control of switches. In both the
p~ssive saturable reactor circuits and in the switched
vertical deflection circuit according to the aforementioned ;;~
copending application, side pincushion correction is
obtained by loading the high voltage transformer of the
horizontal deflection system during the horizontal
retrace time. In order to obtain correctly shaped side
,~ :
~0~2354 RCA 70,334
1 pincushion correction,the loading of the high voltage
transformer is modulated at the vertical deflection rate, as
by the vertical deflection current. Thus, maximum loading
occurs at the top and bottom of the picture and minlmum
loading occurs at the center of the picture.
The variable loading of the horizontal retrace
pulse at the vertical rate results in the generation of a
further pincushion distortion, known as inside pincushion
distortion to distinguish from the outside or peripheral
pincushion distortion ordinarily referred to. This further
pincushion distortion occurs within the raster as a result
of time modulation of the start of horizontal scan caused
by the vertical rate loading. Increased trace duration
resulting from time modulation of the horizontal retrace
15 pulse at the top and bottom of vertical scan increases the .
portion of the resonant period of the deflection coil 26
with S correction capacitor 28 subtended during trace.
Thus, the inside pincushion distortion appears in the reg1on
between the center line and the extreme left and right
sides of the picture as an insufficient pincushion correction.
The amount of inside pincushion correction depends
upon the geometry of the picture tube and on the amount of
outside pincushion distortion requiring correction. With the
advent of wide-angle large viewing screen picture tubes it
has been found that the inside pincushion distortion may be
objectionable to the point that correction is required.
A prior art arrangement for the solution of the
inside pincushion correction problem, in addition to structure
utilized for conventional pincushion correction, uses a
separate saturable reactor or transductor in series with the
~flZ35~ ~c A 70,334
I horizontal defl~ction wlnding. The con-trol winding of the
saturable reactor is driven by a vertical deflection ra-te
signal and modulates the inductance of the horizontal
deflection circuit to correct for the change in "S" shaping
and thereby correct the inside pincushion distortion. This
prior art solution has disadvantages which include critical
design of the saturable reactor, temperature dependence of
the saturable reactor, cost of the saturable reactor, and a
control range so limited as to oEten be insufficient to
compensate for construction tolerances.
~ pincush~on correction c~rcuit ~n acco~dance
with an embodiment of the present lnvention includes an
impedance coupled in series with a horizontal deflection
winding. The impedance circuit contains two branches, a
15 first branch connected between first and second terminals, ?
and a second branch connected between the first and a third -~
terminal, one branch of which is always in series with the
deflection winding. The second branch of the impedance
circuit is paralleled with the first branch by a controllable
20 switch. The controllable switch is gated on at a time during
the second half of the horizontal retrace interval. The time
during the second half of the horizontal retrace interval at
which the switch is gated on is progressively advanced during ~ ,
a first portion of the vertical scan interval and is
25 progressively retarded during the second portion of the
vertical scan interval.
In the drawings:
FIGURE 1 is a representation of a television raster
showing inside pincushion distortion;
FIGURE 2 is a diagram, partially in block and
partially in schematic form of a portion of a television
receiver embodying a pincushion correction ci ~ it according
~4
: '
~0~23S4 RCA 70,334
I to the invention;
FIGURE 3 shows voltage and current waveforms occur-
ring in the pincushion correction arrangement of FIGURE 2
durin~ operation over one vertical interval;
FIGURE 4 is a schematic diagram of a firSt
embodiment of a portion of the pincushion correction
arrangement of FIGURE 2; and
FIGURE 5 is a schematic and block diagram oE a
second embodiment of a portion of the pincushion correction
arrangement of FIGURE 2.
FIGURE 1 illustrates inside pincushion distortion
as it appears on a television raster displaying a crosshatch
line pattern indicated generally by 10. The right and left
sides of the crosshatch pattern are defined by vertical lines
12 and 14. Lines 12 and 14 are straight, indicating that the ;-
raster is East-West outside pincushion corrected by the ;
invention in a manner described below. Vertical grid lines
16 and 18 lying between the center and the sides of the
raster are curved, as indicated by their departure from the
straight dotted lines, indicating the presence of inside
pincushion distortion.
FIGURE 2 shows the deflection system of a television
receiver including synchronizing signal separator 20 which
receives composite video sign~ls from the video detector,
not shown. Separator 20 separates vertical synchronizing
signals from the composite video and applies them to an
input terminal of a vertical deflection generator 22. Vertical
deflection generator 22 uses the vertical synchronizing
signals to generate a vertical deflection current for
lV~32354
RCA 70,334
1 application to a vertical deflection winding, not shown,
connected to the output terminals Y-Y of yenerator 22.
Synchronizing signal separator 20 also separates
horizontal synchronizing signals from the composite video
and applies them to an input terminal of a horizontal
deflection generator 24. Horizontal generator 24 processes
; the horizontal synchronizing signals to produce a generally
~ sawtooth current through horizontal deflection winding 26.
; "S" shaping of the horizontal deflection current is
10 produced by a capacitor 28 coupled in series with horizontal `
deflection winding 26. A horizontal scanning rate voltage
illustrated as waveform 34 having retrace pulse~ 35 appears
across the series connected horizontal deflection winding and
the S capacitor during operation. A retrace capacitor 13 is
coupled from the junction ~f capacitor 28 and horizontal
generator 24 to ground or a similar reference potential.
The horizontal deflection winding 26 is also coupled
in series with a pincushion correction circuit, in this
embodiment speci~ically an inside-outside pincushion
correction circuit, indicated generally by 30 and which
includes an impedance circuit 31 and switch 40. Impedance
circuit 31 has a first terminal 32c coupled by conductor 27
to horizontal deflection winding 26, winding 32b coupled in
a first branch between the first terminal 32c and ground, a
third terminal 37, and a coupling circuit including capacitor 36
and inductor 32a connected in a second branch between the
first terminal 32c and the third terminal 37. Tap 32c -
divides inductor 32 into magnetically coupled upper winding
32a and lower winding 32b. A leakage inductance is
associated with windings 32a and 32b. This leakage inductance ;
decouples windings 32a and 32b so that currents having ~ -
differing waveshapes can flow from tap 32c through the
~6
:
RCA 70,33~
~O~lZ3S4
1 windings. Resistor 33 has a high resistance and damps
transformer 32 to prevent undesirable oscillations.
A controllable switch designated generally as 40 is
coupled in series with the branch of impedance circuit 31
containing capacitor 36. This controllable switch is a
bidirectional thyristor-diode switch having a diode 42
coupled in parallel with a thyristor 44. Switch 40 can be
an integrated thyristor-rectifier (ITR). The cathode of
diode 42 and the anode of thyristor 44 are coupled together
and to capacitor 36, while the anode of diode 42 is coupled
to the cathode of thyristor 44, and both are coupled to a
reference potential.
Switch drive control circuit 46 is coupled to an
output terminal of horizontal deflection generator 24 for
receiving synchronizing information at the horizontal deflect-
ion rate. Such information is in the form of periodic
horizontal retrace pulses similar to illustrated portion 35 of
waveform 34. Switch drive control circuit 46 is also coupled
to an output terminal of vertical deflection generator 2~ for
receiving vertical rate signals. Switch drive control circuit
46 processes the vertical and horizontal-rate synchronizing
information and produces a repetitive sequence ~llustrated as
48 of pulses 50 in a manner described below. The sequence
of pulses repeats at the vertical deflection rate.
Pulses 50 occur during the second half of each
horizontal retrace pulse interval. The trailing edge of
individual pulses 5Q of pulse sequence 48 oCcurSat the time
of termination of the retrace pulse. At the beginning of
each repetitive sequence 48, corresponding to the top of
the vertical scan, the leading edge of each pulse 50 occurs
immediately prior to the tralling edge, so the pulses 50 are
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~08~3~ RCA 70,334
1 short in duration. Pulses 5~ occurring after the beginning
of vertical scan but before center of vertical scan having
leading edges which are progressively advanced in time
relative to the trailing edge. At the center of vertical
scan, corresponding to the middle of the sequence of pulses
48, the leading edge of the individual pulses 50 approach
the time of the center of the retrace pulse 35.
rom the center of the sequence 48 of pulses to
the end of each sequence, which correspond to the middle and
10 the bottom of vertical scan, respectively, the leading -
edges of the pulses 50 are progressively retarded relative ~ ;
to the time of center of retrace, until at bottom of
vertical scan maximum retardation of the leading edye
occurs, and the duration of a pulse 50 is again short.
Accordingly it can be seen that the pulses 50 progressively
increase in duration from beginning to middle of vertical
scan, and progressively diminish in duration from the middle
to the end of vertical scan~ Repetitive sequence 48 of
pulses 50 is coupled from switch drive control circuit 46
to gate 45 of thyristor 44.
Pincushion correction circuit 30 comprises a
switch-variable impedance coupled in series with deflection ;
winding 26. When switch 40 is open, pincushion correction
circuit 30 presents the high inductive impedance of
winding 32b in series with the deflection winding. When
switch 40 is closed, circuit 30 presents a low capacitive
impedance in series with deflection winding 26. This
arrangement corrects for both inside and outside pincushion
distortion.
The average impedance presented to deflection
--8--
~08Z3S~L
RCA 70,334
1 winding 26 by pincushion correction circuit 30 at the top
and at the bottom of the raster is high because switch 40 is
closed relatively late by pulse 50. At the center of the
raster, corresponding to the center of the vertical scanning
interval, the average impedance presented by pincushion
correction circuit 30 is relatively low, because swltch 40
is closed relatively early during the second half of the
horizontal retrace interval.
At the top and at the bottom of the raster the
late closing of switch 40 during the second half of the
horizontal retrace interval and resulting high average
impedance in series with deflection winding 26 reduces the
deflection current I26 flowing in deflection winding 26.
This results in reduced horizontal trace width at the top and
at the bottom of the raster, or outside pincushion distortion~
correctlon. Also, the increased impedance of deflection
winding 26 in series with pincushion correction circuit 30
results in decreased loading of the hori~ontal retrace
pulse. This decreased loading increases the duration of ~`
the horizontal retrace pulse, which tends to compensate
for the change in "S" shaping caused by the time modulation
of the horizontal retrace pulse resulting from the previously
described prior art pincushion correction arrangements. Thus
the variation in impedance of pincushion correction 30
appearing at tap 32c corrects for-both inside and outside
- pincushion distortion.
During the second half of the horizontal retrace
interval, retrace capaci~or 13 supplies energy in the form ~ -
of current I26 to deflection winding 26 in series with
pincushion correction circuit 30. During that pOrtiGn of the
.... , .................. ., , :
, '! -' :,, : ' ' '
' ' : ' '
~L08235~
RCA 70,33~
1 second half of the horizontal retrac2 interval when switch
40 is open, no current can flow in the branch of impedance
circuit 31 containing capacitor 36. Thus, the only path for
; deflection current I26 is through the high inductive
impedance of windin~ 32b. This results in a relatively
high voltage appearing at tap 32c during the second half of
the horizontal retrace interval. Referrina to FI~,URE 3e, thi~ ;~
is illustrated by pulse 56. At the instant when switch 40
is closed by application of a pulse 50 to gate 45 of
thyristor 44, the impedance at tap 32c decreases abruptly as
deflection current I26 divides, with a portion of I26
continuing to flow in winding 32b and the remainder flowing
through winding 32a and capacitor 36 as I36. This decrease
in impedance results in an abrupt decrease in the voltage at
tap 32c at the instant that pulse 50 is applied, as can be
seen in FIGURE 3e by the lagging edge of pulse 56 of tap 32c -~
voltage waveform 54. -
Current begins to flow in the branch of impedance
circuit 31 containing capacitor 36 at the instant that
20 switch 40 closes. Current I36 continues to increase during ~;
the remainder of the second half of the horizontal retrace -
.. ..
interval. Since switch 40 closes relatively late at the top ~;
and bottom of the raster compared with the center of the
raster, current I36 at the end of the horizontal retrace
interval is smaller at the top and at the bottom of the
raster than at the center of the raster. Consequently, ; ;
more of deflection current I26 flows in the branch of
impedancecircuit 31 containing capacitor 36 at the center of
the raster than at the top and at the bottom. This can be
seen by reference to FIGURE 3f, where the left and right
--10--
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~ 23S~
RCA 70,334
1 sides of the waveform correspond to top and bottom of the
raster respectively.
Due to the coupling between deflection current I26
and capacitor current I36 attributable to transformer 32,
deflection current I26 and capacitor current I36 increase and
decrease in consonance during the trace interval. However,
the relative mag~itudes of I26 and I36 during -trace are
determined by the closing time of switch 40 during retrace.
Because of the coupling between current I~6 and current I36,
capacitor curren~ I36 decreases to zero at the center of
the horizontal trace interval, and begins to increase in
the negative direction during the second half of the
horizontal trace interval. During the second half of the
horizontal trace interval, diode 42 of switch 40 conducts
current I36, and thyristor 44 is open. At the end of the
horizontal trace interval, d0flection current I26 and
capacitor 36 current I36 g to zero, as can be seen by
comparing deflection current waveforms 58 of FIGURE 3g and ~ -
currqnt I36 of FIGURE 3f. Diode 42 opens, and thyristor 44
is open because no gating pulses are applied so switch 40
; opens during the first half of the horizontal trace
interval in preparation for a new cycle.
Capacitor 36 is in series with a portion I36 f
deflection current I26 during the entire trace interval.
Capacitor 36 causes S correction of current I36. The amount
of additional S correction of deflection current I26
provided by capacitor 36 depends upon the proportion of
capacitor current I36 to the deflection current. At the
top and at the bottom of the raster, capacitor current I36
is relatively small because of late closing of switch 40.
--11--
10~23~ RCA 70,334
I Consequently, capacitor 36 provides less S correction of
deflection current I26 at the top and at the bottom af
raster than at the center of the raster, where early closing
of switch 40 allows greater current flow in capacitor 36.
Thus, as shown by waveform 60 of FIGURE 3g, control of
switch 40 provides variation in S corr~ction as a function
of the vertical scan.
Adjustment of the size of capacitor 36 determines
the nature of the S correction provided. When capacitor 36
is adjusted to make capacitor current I36 of the same
frequency as deflection current I26, pincushion correction
circuit 30 enhances outside pincushion distortion correction.
When capacitor 36 is made smaller, so that capacitor current
I36 contains higher frequency components than deflection
,
current I26, inside pincushion distortion correction is
provided. Capacitor 36 cannot be made arbitrarily small,
because picture compression at the external line or left
of the raster begins to accompany the pincushion distortion.
This compression begins to occur where the conduction angle
of capacitor current I36 during trace is about ~20,
; corresponding to a frequency of 12KHz.
A particularly advantageous configuration of
pincushion correction circuit 30 occurs when tap 32c is a
center tap on transformer 32. In this arrangement, the -
impedance presented at tap 32c when switch 40 is closed is
the reactance of capacitor 36 in series with the leakage ~ `
inductance of transformer 32, because substantial cancellation
of the flux in windings 32a and 32b occurs. In effect, the
reactance of capacitor 36 appears in series with deflection
winding 26 during trace with an apparent magnitude determined
by the conduction time of switch 40.
..
RCA 70,334
:~01~23S~
1 Other embodiments of impedance circuit 31 will also
provide pincushion correction. Outside pincushion correction
can be provided by an impedance circuit consisting of an
imp~dance such as a resistor, inductor or capacitor coupled
between first (32c) and second ~GND) terminals connected in
series with the deflection winding, paralleled by a direct
connection from first ~32b) to third (37) terminals and by
a control switch (40) as described. Also, a further impedance
could be placed in series between first and third terminals
and in series with the switch to reduce switch current and/or
avoid energy dissipation. As a further alternative, the
further impedance might as in the impedance circuit 31 include
two impedances, an inductor and a capacitor.
FIGURE 4 shows in schematic form a circuit suitable
for use as switch drive control circuit 46 in conjunction
with a conventional v0rtical deflection system. Circuit 46
compares a vertical-rate parabola with a horizontal-rate
sawtooth to produce voltage wave~orm 48 having pulses 50
which progressively advance in time during the first half
of vertical trace and which are progressively retarded during
the second half of trace for application to switch gate 45
of FIGURE 2.
Vertical de1ection generator 22 comprises a class B
push-pull vertical deflection amplifier 106 and vertical
aeflection coil and top-bottom pin correction circuits 108
serially coupled with a deflection coil coupling capacitor 110
and a current sampling resistor 112. A feedback path is
coupled from the junction of capacitor 110 and resistor 112
to the deflection amplifier 106.
A vertical-rate parabola appears in known manner
across capacitor 110 and resistor 112 during operation. This
-13-
~L013Z3S4 RCA 70, 334
1 vertical-rate parabola is coupled to the base of a transistor
104 of a differential amplifier 100 of switch drive control
circuit 46 by way of a pincushion amplitude control resistor
114 and resistor 116.
; 5 Horizontal-rate retrace pulses 35 are coupled to
the base of a transistor 102 of differential amplifier 100
from horizontal deflection generator 24 by way of diode 118
and resistor 120. The base of transistor 102 is also
coupled to a sawtooth forming capacitor 122 and a charging
resistor 124 by way of a pedestal forming resistor 126. ;
In operation during the horizontal trace interval,
diode 118 conducts, thereby maintaining transistor 102
~ conductive and capacitor 122 discharging. Transistor 104 is
- nonconductive because of bias by resistor 128. With
transistor 104 nonconductive, no voltage appears across
resistor 130 for coupling through emitter follower
transistor 132 to gate 45 of thyristor 44.
During the horizontal retrace interval, the
positive-going voltage pulses coupled to the cathode of
, 20 diode 118 render it nonconductive. This opens the discharge
path of capacitor 122, which then begins to charge as can be
seen from voltage waveform 132 of FIGURE 3b. Also, the
constant current flow through resistor 126 stops due to
nonconduction of diode 118 and the base voltage of
transistor 102 rises abruptly. Referring now to FIGURE 3c,
the pulses occurring during the horizontal retrace period
at the base of transistor 102 are shown generally by 134.
Each individual voltage pulse consists of a pedestal created
by resis~or 126 and a superimposed ramp portion created by
the charge of capacitor 122 through resis~or 124. Thus the
arrangement of diode 118, resistors 120,124 and 126 and
capacitor 122 constitute a ramp-on pulse generator.
' '' , ~
S4
RCA 70,334
1 FIGURE 3c also shows a shallow parabola 136 which
represents the voltage applied to the base of transistor 104
of differential amplifier 100 from vertical deflection
generator 22. The parabola 136 intersects the ramp portion
of pulses 134. When the parabola 136 is more negative than
the pulses 134 applied to base 102, transistor 10~ will turn
on and provide an output pulse to thyristor 44 by way of
emitter follower 132. When parabola 136 is more positive
than pulses 134, there is no output to thyristor 44
The most negative portion o parabola 136 occurs at
the middle point of vertical trace. Consequently, the
parabola will intersect the sawtooth and thereby provide a
pulse 50 of FIGURE 3d output at a time which is most advanced
relative to the horizontal retrace pulses at the center of
vertical scan. At the top and bottom of vertical scan,
parabola 136 is most positive and intersects pulses 134 -
relatlvely ~te, producing a pulse 50 output of relatively
short duration.
The points of intersection of parabola 135 with
20 the pulses 134 can be adjusted by means of resistor 138. `~
Resistor 138 adjusts the base bias of transistor 104,
thereby shifting the parabola 136 relative to the pulses at
the base of transistor 102. This in turn results in all the
gating pulses 50 being advanced or delayed by the same
amount, thereby causing a constant change of picture width.
The change in picture width occurs when circuit 30 is
dimensioned to provide a large pincushion correction, in ~ -
which case raster correction does not require the entire
interval of the second half of retrace. An offset of the
vertical parabola moves the turn-on time of switch 40
within the second half of retrace, changing the energy in the
-15~
RCA 70,334
I deflection winding at start of trace. Resistor 140 in
conjunction with resis-tor 142 sets the basic base bias for
transistor 104.
Resistor 114 in conjunction with resistor 116
determines the magnitude of the vertical parabola 136
applied to the base of trans1stor 104. It should be noted
that correction of trapezoidal distortion of the raster can ~
be achieved by connecting a suitable capaci.tor 115 across ;
resistor 116 and/or by connecting capacitor 117 from the
10 junction of resistor 114 and 116 to ground. Connecting a
capacitor across resistor 116 advances tha phase of the vertical
parabola at the base of transistor 104 while a capacitor
from the junction of resistors 114 and 116 to ground delays
the parabola~ An advancing phase moves the point of maximum
pincushion correction upward from the center of the raster
towards the top, and phase delay moves the maximum point
towards the bottom. This in turn results in trapezoidal ~,
correction.
Another embodiment of the switch drive control
circuit 46 for use in conjunction with a switched vertical
deflection circuit such as that described in the aforementioned
copending application is shown in FIGURE 5. Switch drive
control circuit 46 of FIGURE 2 includes a parabola
generator designated generally by 300 and a pulse generator
designated generally by 320 as shown in FIGURE 5. Parabola
generator 300 and pulse generator 320 receive retrace pulses
illustrated as 35 from horizontal deflection generator 20/ by
way o~ transformer winding 203d and a pulse waveform 330 fro~
the switched vertical deflection modulator circuit. Pulse
generator 320 produces switch gate voltage waveform 48 for
-16-
:.
~08Z3S4
RCA 70,334
1 application to thyristor ~ of pincushion correction circuit
30.
As described in the aforementioned copending
application, horizontal deflection genera-tor 207 responds to
horizontal synchronizing pulses 205 to produce a generally
sawtooth horizontal deflection curren-t in deflection winding
26 deployed about kinescope 210. Winding 26 is serially
coupled with pincushion correction circui-t 30 as described
in conjunction with FIGURE 2. ~Iorizontal deflection generator
I0 207 also drives horizontal output transformer 208~Transformer -
208 has two secondaries, 208b and 208e, whieh produce
oppositely~poled horizontal retrace pulses for eharging
eapaeitor 215. Transformer seeondary 208b coupled in series
with thyristor 213 and with eoil 214 begins to eharge saw-
tooth capacitor 215 during eaeh horizontal retrace pulse.
; Thyristor 213 is gated on for a maximum interval of each
horizonta~ retrace pulse at the top of vertical scan. During
the first or top half of scan, gating pulses 231 applied to
; the gate of thyristor 213 by top-of-scan pulse width modulator
273 progressively decrease the conduction time of thyristor 213.
Consequently, a decreasing voltage waveform 227
appears across capacitor 215.
During the seeond half of vertical sean, bottom-of-
sean pulse width modulator 281 gates thyristor 217 with
gating pulses 232 which progressively increase in duration.
Consequently, during the second h~f of vertical scan, thyristor
217 in conjunction with transformer secondary 208c and coil
216 charge capacitor 215 with an increasing negative voltage.
The voltage 227 appearing across capacitor 215 is integrated
by vertical deflection coil 218 to form a substantially
~ ; ~
-17- ~
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~0~3~ RcA 70,334 -
. ~
I sawtooth deflection current.
Vertical sawtooth generator 220 responds to :
vertical synchronizing pulses 221 and to the current through ;
deflection coil 218 to produce oppositely poled vertical-rate
waveforms 269 and 270. Modulators 273 and 281 are driven by
voltages 269 and 270 from generator 220. A ramp-on-pedestal
pulse voltage waveform generator 335 which may be similar to
the ramp~pedestal pulse generator described in detail in
conjunction with FIGURE 4 is driven by horizontal retrace
10 pulses 35 from transformer secondary 208d. Modulators 273
and 281 have second inputs driven by voltage waveform 334
from generator 335. Pulses 334 are similar to inverted
pulses 134 of FIGURE 3c. Pulse width modulators 273 and 281
produce as first output signals the progressively varying : :
15 width pulses 231 and 232 respectively for application to ~
thyristors 213 and 217. ~-
Pulse width modulators 273 and 281 have second :~
output slgnals, obtained from transistors 272 and 280 ~ :
respectively, the collectors of which are coupled through
20 resistor 336 to groundr A voltage 330 representing the sum
of the output voltage waveforms of transistors 272 and 280
appears as an input waveform to parabola generator 300.
Pulse waveform 330 is applied to normally saturated
amplifier transistor 301. The tips of the pulses 330 bring :~
transistor 301 out of saturation, creating positive pulses
at the collector of transistor 3010 A diode 302 coupled from
collector to base of transistor 301 improves the transient :
response of transistor 301. A detector diode 303 couples
the positive pulse output of transistor amplifier 3Ql to an
integrating capacitor 304. A parabolic voltage 306 appears : -
: ,
-18-
:
~0~!3235~
RCA 70,334
I across capacitor 304 representing the integrated output of
transistor 301, with the peak of the parabola occurring at
the center of vertical scan in response to the maximum
duration of the pulse tips of waveform 330. Variable resistor
308 adjusts the rate of discharge of integrating capacitor
304. The vertical rate parabolic waveform 306 is coupled
from capacitor 304 by an emitter follower sta~e designated
generally as 310. A low pass filter designated generally
as 312 attenuates horizontal-frequency currents of the
parabolic waveform 306. A shape control resistor 314
couples a parabolically varying current 316 to pulse processor
320 in response to parabolic voltage 306.
Pulse processor 320 receives horizontal retrace
pulses 35 from transformer secondary winding 208d for
application to the base of inverting amplifier 322. The
negative-going pulse output of inverting arnplifier 322 is
applied to the base of transistor 324 by way of capacitor 328
and diode 326.
Transistor 324 also has applied to its base the
parabolically varying current waveform 316. Current wave~orm
316 tends to maintain transistor 324 conductive between
horizontal retrace pulses. Upon application of a negative-
going horizontal rate pulse ~rom inverter 322, transistor 324 -~
ceases conduction for a period dependent upon the time
required for current 316 to charge capacitor 328 to again
forward-bias transistor 324. The nonconduction period of
. . .
transistor 324 will be least in the center of vertical scan
at which time current 316 is greatest, and nonconduction of
transistor 324 will have the greatest duration at top and
bottom of vertical scan.
--19--
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,. . :
~8Z3S4 RCA 70,334
1 The positive-going pulse output of transistor 324
is taken from the collector and applied to the base of
transistor 340 through resistor 342. Another input signal to
the base of transistor 3~0 is taken from the output terminal
of amplifier 322 through resistor 3A4. A positive pulse
output at the collector of transistor 340 occurs only when
the output signals of both amplifier 322 and transistor 324
are low. A pair of inverting amplifiers couples the pulse
output of transistor 340 to the gate of thyristor 44.
Since the lagging edge of the pulse output of
`; amplifier 322 occurs at the end of the retrace pulse interval,
the output pulse from transistor 340 ends at the end of
retrace pulse interval. The pulse output of transistor 340
has a duration which is maximum at center of vertical scan
and minimum at top and bottom of vertical scan.
The described pincushion correction circuit
simultaneously corrects inside East-West pincushion distortion
and outside East-West pincushion distortion. It is also
highly efficient because loading of the horizontal output
transformer is avoided. The described circuit may be used
in conjunction with conventional pincushion correction
circuits.
When used in conjunction with the switched mode
vertical deflection system as disclosed in the aforementioned
copending application, the disclosed pincushion correction
circuit is par~icularly advantageous. While the switched
mode vertical deflection circuit provides side pincushion
correction
distortion~by loading of the horizontal retrace transformer,
in some applications it is necessary to provide for
simultaneous conduction of the control switches such as 213
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~(~823S4
RCA 70,334
l and 217 of FIGURE 5 at center of vertical scan in order to
achieve sufficient inher~nt pincushion correction. Such
simultaneous conduction of switches 213 and 217 creates a
dissipative current path for the horizontal retrace energy.
By use of the present invention in conjunction with the
switched mode verticai deflection system the dissipative
energy loss is avoided and a very low total power consumption
is achieved.
The following is a listing of values of circuit
elements providing pincushion correction for a 110 large-
screen kinescope such as the RCA Corporation model
number A67-610X:
L26 0.28mH
L32 core ~lOx 45mm, N22
each half one layer of 34 turns of
0.8mm Cu wire, 60~H each half,
leakage l~H.
C36 l~F
C122 0.015~ F ~ ~
C304 4700pF ` :~:.
C328 470pf
~)33 680 ~
R114,116,120,124 4K7 ::
Rl26 lK ~ `
R128 3K3
R130 lOK
R138 4K7 variable
R140 3K9
R142 4K7
R308 lOOK ~:
R314 22K
R342,344 4K7
,:
-21-
.
:: - - . :
. - ::: :. -
2354
RCA 70,334
1 For the above values and kinescope, current components in
the deflection winding due to resonance of the S capacitor
and deflection winding were observed at about 6.5 kHz, while
components due to the pincushion correction circuit were
. 5 observed to be at about 12 kHz. .'
:~ 10
,
, :
.~
; 20
,.
., '
-22-
:
. . - ~.
