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Old 3rd Mar 2006, 8:06 pm   #18
tubesrule
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Join Date: Jul 2004
Location: Michigan USA
Posts: 325
Default Re: PC as a standard convertor

Jeff,
There are indeed two IC's on the bottom of the converter; the second modulator chip, and the image FLASH ROM. It was a tough decision to go double sided mounting, but the circuitry dictated it. By putting the second modulator chip directly under the first one, both output pins are positioned as close as possible to the RF connector/combiner circuitry. The FLASH is in a VSOP32 package, and it would have wasted a great amount of top side area to connect it to the VQ100 fpga. By placing it directly under the fpga, the pins on the FLASH practically connect directly to the pins on the fpga directly above it. These short interconnects also help with the high frequencies used in this converter. The FLASH bus will run as high as 36MHz, with internal frequencies of the fgpa reaching over 106MHz for the 819 line output. These high frequencies were required to oversample the output enough to reduce filter requirements.
Engineering for the converter is complete, and it will be possible to program a unit for the following standards (each unit can only support one standard and one RF System at a time):

PAL->405/25
PAL->441/25
PAL->455/25
PAL->625/25
PAL->819/25
NTSC->343/30
NTSC->441/30
NTSC->525/30

I have also already calculated tables for all System A, E, F, and early/late M frequencies. I can add System L if someone requires this. So far, 4 switch positions are dedicated to setting 15 channel frequncies plus modulator off, one switch is for equalization pulse enable/disable for standards that did not originally have eq pulses, and one switch for disabling the converter so the unit can be used as a stand alone modulator. In this mode, a sound trap filter is provided on the video input, but no additional video filtering is done.
That leaves two switch positions left for future options. If anyone has suggestions for these, possibly more channels, I welcome the feedback.

Darryl
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