April 10, 2009

Sensor interface in 373

by Andrey Filippov

I’m considering using Xilinx high speed Serial I/O – 4 of the GTP in XC6SLX45T in CSG324 package (15mm x 15mm) to interface the sensor boards – it can be very attractive to be able to migrate to higher performance sensors from the current Aptina 5MPix ones.  It would also enable higher bandwidth to the next version of the 10359 board – up to four of 3Gb/s channels, reduce EMI and enable longer cables.

The problem is that normally you need a large chip on the other (sensor) end capable of encoding data in a way compatible with the GTP – it would be an overkill for the simple CMOS sensor module. But it seems there is a way to use a tiny (5mm x 5mm) 3 – channel (plus clock – total 4) Texas Instruments SN65LVDS301 FlatLink(tm)3G that encodes 24 bit parallel data plus 3 sync signals into serial data. Maximal “pixel” rate – 65 MHz (not enough for MT9P031) but with additional register or better CPLD (like XC2C64A in CP56 6mm x 6mm package) it would be possible to double the pixel rate and add some scrambling to reduce disparity – not that critical as the data rate per pair would be only 480Mb/s. It seems that it would be possible to make GTP to accept that slow data rate, bond 4 channels (each still has to be able to recover it’s own clock) and use SN65LVDS301’s clock as a master in this bonding with a comma mask ox 10’b1111111111 and comma pattern of 10’b1111100000.

Most likely I’ll still use smaller XC6SLX25 (w/o “T”) first and use the bank that has GTP-s in 45T to connect the 30-pin parallel flex connector (compatible with the 10353 and the existent sensor boards) first, upgrading to high speed serial I/O in the next revision/model. that will be rather simple task as it will not require major PCB redesign – FPGA is side-by-side with the sensor connector, so those traces do not intersect with other ones.

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