WhiteP85
Member
Still waiting for the parts to arrive and if I get them soon I might be able to perform some initial testing this weekend.
.....
Hopefully we will be lucky and this will work first time.
The mission is not over ...
The bad news is that the first design does not work and it is going to take a bit more effort to make and test some modifications and get it right.
For the technical folks here are the issues:
1. The LVDS crosspoint switch I used did not work. It is a 1.5 Gbps device and this LVDS signal may be as high as 2.5 Gbps (I am working a little in the dark as I have no equipment (spectrum, network analyzer etc) to check it).
2. Even if I used a higher frequency 2.5 Gbps LVDS crosspoint switch it will not work if the control signal is being used (as I suspect) as the crosspoint switches are for one-way signals only. The MAX9259/MAX9260 Serializer/Deserializer chipset used in the Tesla camera includes an integrated control signal in the reverse direction so crosspoint switches will not pass the control signal.
3. The high-side switch I selected is designed for much higher currents and does not work. The data sheet is a bit fuzzy so I will try something else.
So my next step is to prototype the following:
1. Use two-way 50 ohm 0-4 GHz diode switches (http://www.psemi.com/pdf/datasheets/pe4283ds.pdf) in place of the crosspoint switch to switch the LVDS signal. These are the types of switches used in cell phones and the LVDS signal is of much lower power so should work just fine.
2. Use a more suitable high side power switches (http://www.st.com/web/en/resource/technical/document/datasheet/CD00128782.pdf).
I will order these new parts, along with some adapter boards, and wire them to the existing PCB taking into account the required signal integrity by using 100 ohm twisted pair for the LVDS jumpers. As a quick test I removed the crosspoint switch and jumpered the rear LVDS signal and the camera worked just fine. This indicates that my traces are ok although I will be changing them in the next layout from differential to single ended as shown below. I should also mention that I was able to tap into and regulate the LVDS power, so it will be handy not to have to wire in 12 V externally.
Here is the initial design of the second generation boards. The large traces are 50 ohms using the same standard FR4 PCB to keep cost down. I can get prototype 2-later FR4 PCBs made in about a week for less than $200 but more expensive 4-layer boards needed for narrower traces cost much more or take much longer. I will not be making these until I have prototyped them using the existing boards.
As always - suggestions are welcome.
Thanks for hanging in there.
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