DLP7000: how to achieve maxim pattern rate for DLP7000 8bit greyscale

Hello HT,

Welcome to the DLP section of the TI-E2E community.

To help understand let's look at the limiting case in which we load and "reset" the DMD at the fastest possible Global reset rate.  For the DLP7000 this comes out to 43 µs per bitplane.  For one 8-bit grayscale frame that will be 8 x 43.22 µs = 345.76 µs which gives about 2.89 kHz - again this is the limiting case, utilizing Global reset with modulated illumination

Now during each bitplane we must have the modulated illumination:

• MSB -- on for the whole 43.22 µs bitplane time
• MSB - 1 -- on for 1/2 of the bitplane time
• MSB - 2 -- on for 1/4 of the bitplane time
• MSB - 3 -- on for 1/8 of the bitplane time
• LSB + 3 -- on for 1/16 of the bitplane time
• LSB + 2 -- on for 1/32 of the bitplane time
• LSB + 1 -- on for 1/64 of the bitplane time
• LSB -- on for 1/128 of the bitplane time

Now if we arrange the order of bitplanes as MSB, LSB, MSB-1, LSB+1, MSB-2, LSB+2, MSB-3, LSB+3, then we switch the source on at the beginning of the MSB bitplane time and then off after 1/128th of the LSB bitplane, back on 1/2 way through the MSB-1 bitplane time and back off after 1/64th of the LSB+1 bitplane time and so on --  It would look kind of like this:

The shortest pulse your illumination would have to achieve is between MSB-3 & LSB+3 which is about 8.1 µs.

Again, this is the limiting case.  Please notice all of the "dark time" in this scheme -- it is a little over 3/4 of the entire 8-bit frame. 

To get to a reasonable "dark time" of say about 1/3 of the 8-bit frame, then display the MSB for 8 times as long.  This means that the 8-bit frame rate will be about 1.22 kHz.  The illumination will be on as follows (since 43 µs is the fastest we can switch the array):

• MSB -- on for 8 * 43 µs
• MSB - 1 -- on for 4 * 43 µs
• MSB - 2 -- on for 2 * 43 µs
• MSB - 3 -- on for 43 µs
• LSB + 3 -- on for 1/2 of 43 µs
• LSB + 2 -- on for 1/4 of 43 µs
• LSB + 1 -- on for 1/8 of 43 µs
• LSB -- on for 1/16 of 43 µs

In this scheme there is only dark time in the last four bits, but the frame time is now 821 µs (hence 1.22 kHz).  The smallest illumination pulse will be about 64.8 µs

This is how to achieve much faster 8-bit display times.

Fizix

If we allow dark time in the last five bits then the frame will be illuminated as follows:

• MSB -- on for 4 * 43 µs
• MSB - 1 -- on for 2 * 43 µs
• MSB - 2 -- on for 43 µs
• MSB - 3 -- on for 1/2 of 43 µs
• LSB + 3 -- on for 1/4 of 43 µs
• LSB + 2 -- on for 1/8 of 43 µs
• LSB + 1 -- on for 1/16 of 43 µs
• LSB -- on for 1/32 of 43 µs

For a frame time of 516 µs which gives about 1.94 kHz.

The 2.8 kHz is the limiting case and would require that you control the illumination with precision and would also have a whopping 75% dark time.  Your µ-controller/FPGA that feeds data to the DLPC410 would have to be able to send formatted data at the rate you require.

Fizix