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Motion Picture Formats Compared to Standard TV and HDTV Formats
To review a bit of cinema and television history, most movies were and are filmed in what is referred to as "wide-screen" format. The Movie Industry uses this format because wide screen is closer to the human eyes' width and height perception. There are many so-called "wide-screen" formats currently in use by the Movie industry. Among the more popular are: 1.85 and 2.35; however, older movies were filmed in many screen ratios including: 1.33, 1.17, 1.375, 1.66, 1.75, 2.21, 2.40, 2.55, 2.59, and 2.76 (These ratios are more correctly written as "1.85:1...etc") Both standard NTSC and SDTV are 1.33:1 (4:3) with High Definition ATSC (16:9) at 1.78:1. Normal US movie screen standards have more or less settled on 1.85:1. There is little to no loss of picture information when converting the most common movie format, 1.85:1 to the HDTV format of 16:9 (1.78:1).
Diode Modulator
The diode modulator is used to correct the inner pin distortion associated with the flat faceplate of true flat tubes. Op-amp U24401provides gain and filtering for the WIDTH_REF line from the deflection SIP. This signal is comprised of a vertical rate parabola riding on a DC level that drives the pin output circuit. C24434 is the S-cap during the top and bottom of the vertical raster. At the very center, the effective value of the S-cap is the series combination of C24423 and C24418. This series combination causes the equivalent value of the S-cap to be less in the middle stretching the raster gradually as the vertical scan approaches the center and gradually decreases as it approaches the end of vertical scan. Because the S-CAP is floating above ground, a "bath tub" shape waveform is required for optimum performance and dynamic focus voltage waveform to maintain a constant peak-to-peak voltage. It is also required that the waveform be phase locked to the horizontal deflection. An interlock provides protection for the horizontal output transistor by routing ground from the Power Supply Deflection (PSD) board through J24401-3 to the deflection SIP. Without this ground, horizontal drive is defeated. T24401 and C24420 form a tuned circuit at twice the scan rate or 4H to give second harmonic correction. R24427, R24428, CR24405, CR24406, and C24419 form a "mouthtooth" damping circuit across the S-Cap. U24402 is used as an error amplifier and a filter. Its output is a DC voltage that is used to drive R24404. This DC voltage is switched to ground by Q24402 at a horizontal frequency. This generates a rectangular voltage waveform that is phase locked to the horizontal frequency. C24422 acts as a phase delay that is used to center the dynamic focus waveform. This rectangular voltage waveform is then buffered by U24402. This buffer also provides constant drive impedance for the double
27 integrator, U24403. The rectangular voltage waveform is then AC coupled into a parabola generator. This generates a horizontal parabola voltage waveform that is locked to the horizontal frequency. The parabola generator consists of U24403, R24414, R24412, R24413, C24408, C24407, C24405, and C24406. The output of U24403-7 is AC coupled into two different paths. The first path couples into a peak-to-peak detector. This consists of CR24402, CR24403, C24410, C24411, R24419, and R24407. It is by this means that the amplitude of the parabola waveform is held constant across different horizontal frequencies. The second path AC couples the parabola wave shape into the wave shaper. This circuit is used to generate the "bath tub". It consists of C24409, R24416, R24417, R24418 and CR24401. U24403 is then used as a buffer in order to drive the high voltage amplifier.