June 1969 Radio-Electronics
[Table of Contents]
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Electronics,
published 1930-1988. All copyrights hereby acknowledged.
A 720-line HDTV display is made up of 1,280 vertical lines and 720 horizontal lines of pixels, which gives a total of 921,600 pixels. A 1080-line HDTV has 1,920 vertical lines and 1,080 horizontal lines, for a total of 2,073,600 pixels. In 1969, a 230 vertical line by 230 horizontal line electroluminescent (EL) flat-screen television display with 52,900 pseudo-pixels was considered a big deal - and it was since it was the starting point for digital flat-screens of today. Interestingly, while the "pixel" distribution was square, the actual display retained the standard 4:3 aspect ratio, meaning horizontal element width was 33% greater than the vertical element. Since each EL element was addressed individually, there was no ability of a picture element to be shared by adjacent "pixels," so displaying a circle would result in a very pixelated picture. A standard cathode ray tube (CRT), while having 525 vertical lines of phosphor "dots," it had effectively an infinite number of horizontal lines since the video intensity signal was analog. The CRT's electron gun, during its sweep, could simultaneously illuminate adjacent phosphor dots, giving a smoothing effect that could render a true circle - even though under close inspection it had a fuzzy edge. BTW, an iPhone 8 Plus display has 1080 x 1920 pixels (same as 1080p HDTV) for a total of 2,073,600 pixels. A Galaxy S8 has 1440 x 2960 pixels (same as 1440p HDTV) for a total of 4,262,400 pixels.
Flat-Screen TV Has 52,900 Picture Elements
Experimental flat-screen set is checked by project director Yoshiyama. Model uses some 8,600 components.
New York - Curious visitors jammed the darkened interior of Panasonic's booth at the March IEEE Show to view TV programs on a screen no thicker than this magazine. The 50-pound experimental set is likely to be a forerunner of flat-screen models that can be hung on walls.
The 8.0 x 10.7 - inch electroluminescent screen has 230 vertical and 230 horizontal electrode strips. A phosphor layer between these strips (diagram, right) provides 52,900 picture elements. The 0.04 x 0.03-inch size of each element maintains the standard 4:3 picture ratio.
Resolution is fair, but the phosphor has a distinct green hue and contrast and brightness are low. Writing in Electronics, project director Masami Yoshiyama compares the image detail to that obtained from some low-cost video tape recorders. Instead of the odd-even scan pattern used in conventional receivers, both fields are successively displayed on the same horizontal lines. This boosts brightness but cuts resolution.
Lumped Video Delay
Screen photo made during IEEE show. Image is a dark green color.
Electroluminescent (EL) flat panel.
Here is how a single horizontal line of the 230 x 230 matrix is scanned. The horizontal electrode receives a negative selecting pulse, while blanking pulses dim the lines not being scanned. Simultaneously, a sampled video signal for the entire line is applied to all the vertical electrodes. This is accomplished with a 50.6-μsec lumped delay line, which holds the video for the scan line until it can be displayed simultaneously when the horizontal pulse is applied.
The brightness of each element is a function of the video pulse amplitude on the vertical strips, varying exponentially, within limits, with the pulse width. The input transistor to each vertical strip serves as a variable resistor, its collector resistance modulated by the sampled video from the delay line.
Then, after one line has been scanned, a counter, triggered by the horizontal sync signal, steps the horizontal pulse distributor to the next line. A second horizontal pulse generator simultaneously delivers blanking pulses to all other lines.
The cutaway drawing of the matrix display panel shows an impedance layer between the horizontal electrodes and the phosphor layer. This reflective coating of barium titanate improves brightness and contrast because of its nonlinear characteristics. The vertical strips are transparent, and the horizontal electrodes are aluminum evaporated.
Panasonic plans to test a display panel with an improved phosphor coating shortly. The zinc sulphide compound used now requires dim lighting for comfortable viewing.
The prototype model demonstrated at the Show was equipped with provisions for video tape recorders and closed-circuit cameras in addition to VHF reception. With circuit modifications, the display system could be adapted for graphic and alphanumeric readouts.
IC's are used in the counter circuits and could simplify the brightness circuits.
Some 8,600 components are used in the set, comparable to the number in a desk-top electronic calculator. Power consumption is about 100 watts.
Posted July 25, 2018