Electron beam intensity profile measuring system and method

A system for measuring the intensity profiles of the electron beams of color kinescopes includes a camera having a CCD. A color field is placed on the kinescope screen and a pixel in the center of one of the colored stripes is selected. The color field is turned off and the beam is scanned in short lines in one direction and incrementally stepped across the selected pixel in the perpendicular direction. The charge level on the selected pixel is representative of the beam intensity and is recorded. The entire beam is stepped across the pixel to measure the intensity profile in one direction. The directions of scanning and stepping are then interchanged to measure the beam intensity profile in the normal direction. The process is then repeated for the other electron beams in the kinescope.

BACKGROUND 
This invention relates generally to the production of kinescopes for color 
television receivers and particularly to a system and method for measuring 
the intensity profile of the electron beams of such kinescopes. 
The screens of many kinescopes are composed of phosphor stripes each of 
which emits a different color of light when impacted by electrons. Each 
kinescope includes an electron gun which provides, electron beams for 
individually scanning each of the color light emitting phosphors. The 
electron beams are scanned across the screen in a raster fashion so that 
each of the electron beams impacts the phosphor which emits the desired 
light color. The electron beams are individually modulated so that the 
primary light colors are combined to produce the desired color at each 
spot on the screen. Because each electron beam must be individually 
modulated in accordance with the intensity of the beam, it is necessary to 
measure the intensity profile of the electron beams to permit optimization 
of the electron beam modulation and other characteristics of the beam. 
A current method commonly used in measuring the electron beam profile 
utilizes a narrow, light transparent slit in an opaque member. The narrow 
slit is aligned with a photomultiplier tube which measures the light 
transmission through the slit. The slit is carefully centered over the 
appropriate color phosphor and the electron beam to be measured slowly 
scans a raster line across the slit. As the raster line passes the slit, 
the output voltage of the photomultiplier tube is proportional to the 
intensity profile of the electron beam. Thus, the intensity profile along 
one axis, for example, the horizontal axis of the beam is indicated by the 
change in output of the photomultiplier tube. The slit is then 
repositioned over a different color producing phosphor line and the 
process repeated until all the electron beams are measured. The slit is 
then rotated 90.degree. and the raster lines are swept in a direction 
90.degree. to that of the original sweeping and the process repeated to 
obtain the electron beam intensity profile in the perpendicular, for 
example vertical, direction. 
The above method of measuring the electron beam intensity profile suffers 
several significant disadvantages. Substantial time and labor are spent 
mechanically positioning the slit over the phosphor stripes of the various 
colors. Thus, the measurement of the profiles of all three beams along 
both the horizontal and vertical axes at one position on the screen 
necessitates the mechanical positioning of the slit six different times. 
Typically measurements are taken at various locations on the screen and 
accordingly the measurements at each location requires the positioning of 
the slit six times. For this reason, substantially more time is spent in 
positioning the slit with respect to the phosphor stripes than is spent in 
actually taking the beam profile measurements. Additionally, because the 
slit is mechanically positioned with respect to the phosphor stripes, the 
accuracy of the measurements is dependent upon the positioning of the 
slit. For these reasons, there is a need for a system and method of 
electron beam intensity profile measurement which is more accurate and 
subtantially less time consuming. The present invention fulfills these 
long felt needs. 
SUMMARY 
A system for measuring the intensity profiles of the electron beams in a 
CRT having a screen composed of triads of phosphors which produce 
different colors of light when impacted by the electron beams includes a 
CCD camera. The camera images a color field which is scanned on the screen 
by one beam while the other color beams of the CRT are off. The center of 
one of the triads is identified and a CCD pixel in the proximity of the 
center of the triad is selected. Means is provided for turning off the 
color field. Deflection means deflects the electron beam whereby the beam 
impacts the screen in the proximity of the selected pixel. Beam bender 
means incrementally steps the electron beam across the pixel in one 
direction and subsequently in another direction normal to the one 
direction while the deflection means scans the beam in short lines in a 
direction substantially normal to the direction of incremental stepping 
whereby the beam is incrementally stepped across the pixel in the one 
direction and then the other direction. The intensity representative 
signal on the pixel for each of the incremental steps is stored whereby 
the intensity profiles of the electron beams in both of the scanning 
directions are measured.

DETAILED DESCRIPTION 
FIG. 1 shows an electron beam intensity profile measuring system 10 coupled 
to a kinescope 11 having a screen 12. The light output of the kinescope 
11, represented by the arrows 13, is directed to a camera 14. The camera 
14 includes a lens 16 which is a standard optical light focussing lens and 
a CCD 17 (charge coupled device). The CCD 17 can be a linear array of 
pixels oriented substantially perpendicular to the phosphor stripes of 
which the screen 12 is composed. Alternatively, the CCD 17 can be a planar 
array of pixels with the pixels being arranged in rows and columns. When a 
planar CCD array is utilized, a row or column which extends substantially 
normal to the phosphor lines of the screen 12 is selected for processing 
and the other pixels are ignored. 
The output of the camera 14 is provided to a data processor 18 over a line 
19. The transfer of data from the pixels of the CCD 17 to the data 
processor 18 is well known to those skilled in the art. The data processor 
18 controls a deflection circuit 21, a gun control 22 and a beam bender 23 
which are coupled to the kinescope 11 by output lines 24, 25 and 26, 
respectively. The deflection circuit 21, the gun control 22 and the beam 
bender 23 are well known commercially available components. The deflection 
circuit 21 is coupled to the yoke 27 of the kinescope 11 and is used to 
scan the electron beams horizontally and vertically across the screen 12. 
The deflection circuit 21 therefore also is used to scan the electron 
beams in the short horizontal and vertical lines needed to utilize the 
present invention as explained more fully hereinafter. The gun control 22 
is used to turn the red, green and blue electron guns within the kinescope 
11 on and off at the appropriate times. The beam bender 23 is used to step 
the short vertical and horizontal scan lines in the appropriate direction 
during the measurement of the electron beam intensity profile in a manner 
described hereinafter. 
In FIG. 2a the CCD 17 is substantially perpendicular to a phosphor stripe 
28. The CCD 17 can be a linear array very similar to that illustrated or 
it can be a particular row or column of a planar CCD array. In either 
event, a pixel PG which lies at the close proximity to the center of the 
phosphor line 28 is selected as the pixel used to measure the electron 
beam profile. The electron beam 29 initially is positioned above and to 
the left of the selected pixel PG. The beam 29 is shown as being 
substantially circular in cross section, typically the configuration is 
elliptical. The electron beam 29 is vertically scanned in short scan lines 
by the deflection circuit 21 (FIG. 1) as indicated by the scan arrow 31. 
At the same time, the electron beam 29 is incrementally stepped to the 
right, as indicated by the arrow 32, by the beam bender 23. As the beam 29 
passes over the center pixel PG the charge level on the pixel PG changes 
in accordance with the intensity of the electron beam in the manner shown 
in FIG. 3. Thus, as shown in FIG. 3 when the center of the electron beam 
passes over the pixel PG, the maximum intensity is realized and the 
minimum intensity is realized when the edges of the electron beam pass 
over the pixel PG. Accordingly the beam intensity profile is measured by 
reading and storing the intensity proportional charge level on the pixel 
PG for the scan lines across the pixel. After the entire beam has passed 
over the pixel PG, the electron beam 29 is repositioned above and to the 
left of the pixel PG and the scanning and stepping directions reversed, as 
indicated by the scan arrow 33 and step arrow 34 in FIG. 2b. Thus, in FIG. 
2b the deflection circuit 21 (FIG. 1) scans the electron beam in short 
horizontal lines, e.g. perpendicular to the phosphor line 28 while the 
beam bender 23 incrementally steps the electron beam vertically across the 
center pixel PG. After the entire electron beam 29 has passed over the 
pixel PG, the intensity profile of the beam in both the horizontal and 
vertical directions has been measured without any mechanical movement of 
any of the measuring elements. Additionally, after the first electron 
beam, for example the green beam, is measured a pixel centered on a blue 
phosphor stripe can be selected and the process repeated for the blue 
beam. A pixel for the red electron beam can then be selected and the 
process repeated. Thus the profiles of all beams can be measured in both 
directions without mechanically manipulating any of the components of the 
system. 
The pixel PG is selected by first scanning one electron beam, for example 
the green beam, to produce a green field across the entire screen 12 of 
the kinescope 11. All pixels of the CCD 17 which receive energy from the 
green phosphors thus are illuminated and charged to a higher level. 
Accordingly it is a simple matter to identify the edges of the green 
phosphor stripes and to select a pixel which is centered with respect to 
one of the green phosphor stripes. The green field is then turned off and 
the short vertical and horizontal lines scanned by the green beam while 
the charge level on the selected central pixel is recorded as indicative 
of the beam intensity for the short lines. After the measurement of the 
green electron beam is completed, the green and red guns are turned off 
and the blue beam is utilized to select a pixel centered on a blue stripe 
and the measurement process repeated. It should be noted that because many 
pixels are illuminated by light from each of the colored phosphors a 
plurality of measurements for each electron beam can be made across the 
face of the screen 12 simply by positioning the electron beam 29 in the 
desired positions with respect to the selected pixels. Thus plural 
measurements can be made without moving the CCD or any other element of 
the system 10. 
In the preferred embodiment of FIG. 4, the measurement begins by turning on 
the green field at step 36. In this state, the deflection circuit 21 of 
FIG. 1 scans the green electron beam across the entire screen 12 to 
produce a green field while the red and blue electron guns are turned off. 
Obviously if desired, the red or blue electron beam can be the first to be 
measured. At step 37, the edges of one of the green colored light emitting 
phosphor stripes is identified and at step 38 a pixel PG which is very 
nearly centered within the phosphor stripe is selected. At step 39 the 
green field is turned off. At step 40 the green electron beam is 
positioned to the left and above the selected pixel PG as shown in FIG. 
2a. The electron beam is stepped right one horizontal increment at step 41 
and at step 42 the beam is vertically scanned one short vertical line, as 
indicated by the vertical scan arrow 31 in FIG. 2a. At step 43, the charge 
level on the pixel PG is investigated to determine whether or not the beam 
passed over the pixel PG. When the pixel PG is not high the beam did not 
pass over the pixel PG and step 41 is reentered and the beam is 
horizontally stepped another increment to the right and vertically scanned 
another short line. At step 43 when pixel PG is high, the beam has passed 
over the pixel and the charge level on the pixel is directly proportional 
to the intensity of the electron beam. The reading is read and stored as 
one of the horizontal intensity profile measurements at step 44. At step 
45 when a sufficient number of horizontal steps has not been completed to 
insure that the entire horizontal dimension of the beam 29 has crossed the 
pixel PG, step 41 is reentered and another horizontal incremental step 
taken to repeat the vertical scanning and beam intensity measurement as 
the beam again crosses the pixel PG. The number of incremental steps 
required is dependent upon the type and size of the kinescope being 
measured and accordingly can be manually input when the kinescope is 
placed into the system 10. However, the rapidity and ease of taking the 
measurement permits a large number of incremental steps to be selected to 
insure that the entire beam 29 crosses the pixel PG. When the selected 
number of horizontal incremental steps has been completed, the electron 
beam 29 is repositioned above and to the left of the selected pixel PG at 
step 46. At step 47 the beam is incrementally stepped vertically as 
indicated by the arrow 34 in FIG. 2b and the beam is scanned horizontally 
across the pixel, as indicated by the arrow 33 of FIG. 2b at step 48. At 
step 49 when the pixel PG is not high, the beam failed to pass over the 
pixel PG and step 47 is reentered to repeat the vertical incrementation of 
the beam and to horizontally scan another short line across the pixel. At 
step 49 when pixel PG is high, the intensity indicative charge level of 
the pixel PG is read and stored at step 50. At step 51 when the number of 
vertical steps needed to scan the full vertical dimension of the beam 
across the pixel has not been completed, step 47 is reentered and the 
vertical incremental stepping and horizontal scanning are repeated and the 
intensity is again measured. At step 51 after the required number of 
vertical steps is completed, the horizontal and vertical beam widths are 
read out at step 52 and the intensity profile of the green beam is known. 
The measurement process is then repeated for the red and blue electron 
beams as indicated by steps 53 and 54.