130 lines
4.6 KiB
Markdown
130 lines
4.6 KiB
Markdown
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Electrical Engineering Change Notes
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===================================
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Revision 0.0
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### Description
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First revision
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### Manufactured
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Boards ordered from Aisler on August 12th 2020.
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Gerbers used are in the repo.
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### Issues noticed
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* The E1 TX pulse were very weak. Probably would have worked but to rise the pulse amplitude
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to 1.5 V, the series resistance were lowered to 27R. (Original iCEbreaker proto had 33R on
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the icebreaker + 47R on the PMOD. The bitsy proto only had the 47R)
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### Notes
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* Kicad files were not kept since it's the same schematic and layout as rev 0.1
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with some value changed and all boards were either built with new values or reworked.
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Revision 0.1
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------------
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### Description
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This revision is mostly just to keep a record of the changes that were applied
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directly on the r0.0 prototypes and how they were assembled.
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### Changes compared to previous revisions
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* E1 TX side resistors changed to 27R (from 82R)
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* Consequently all other uses of 82R were updated
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* PLL filter switched to use 120R
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* Series resistor for clock switched to 27R (which is probably better)
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* Connection from GND to USB shield changed to 91k (from 1k5)
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* All 47R networks were swapped for 33R.
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* New value was picked so that including the UP5k drive impedance (~20R),
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it matches 50R more closely for USB
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* Other places where it's used don't matter much.
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* E1 LED current is dominated by 595 output impedance anyway.
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* 33R is just as fine for serial termination/EMI isolation for GPS signals.
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* Some silkscreen label was added on the PCB
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### Manufactured
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Rev 0.0 PCBs were used and assembled / reworked to match this revision.
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Two boards in total: one for @LaF0rge and one for @tnt.
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### Issues noticed / remaining
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* Flash footprint is wrong. The selected flash is not using the "wide" variant of SO8.
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* The NT/TE selection pin-header is completely wrong
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* The lightpipe is a bit loose. Turns out the holes came out 10% oversized out of Aisler :/
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Dimensions left as the manufacturer ones and hope that the prod are closer to nominal.
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* The E1 bias configuration should probably have been reversed with the `bias_fixed`
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assigned to the `_n` side. This way the variable bias would have been lower and the common
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mode voltage closer to what the comparator expect for LVDS.
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This however would break compatibility with the proto which is a waste and has no real-world
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impact. The common-mode voltage change is minimal and comparator work fine where it is. And
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even if it was an issue we could put the variable bias lower and flip the input polarity in
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the bitstream.
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Revision 1.0
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------------
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### Description
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Production version, sent to manufacturer for production.
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### Changes compared to previous revisions
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* Silkscreen updated
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* Flash footprint updated to narrow SO8 (150mil)
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* Rewired the NT/TE header properly
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* Changed RF trackwidth to 0.175 mm to account for production stackup
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* Changed board outline to cater to connectors being more outward
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* Extended by 0.5 mm on front/back but only in the center part of the PCB
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to avoid interfering wih the silicone ring
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* Reworked the 'tabs'
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* Adjusted the expected end panel position lines to account for 1 mm silicone thickness
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* Adjust positions of connectors / ...
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* Moved RGB led & lightpipe outward by 500u
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* Moved Serial connector outward by 500u
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* Moved USB outward by 500u
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* Moved GPIO RJ45 outward by 500u
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* Moved dual-RJ45 outward by 500u
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* Moved button outward by 750u
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* As a result of those moves some minor adjustments were made
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* Copper fills extended by 500u on the left side + reworked upper corner
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* Copper fills extended by 500u on the right side
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* To avoid the small protrusions in the planes, vias in the RX CT bias were moved inward
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* Rerouted 1v2 on the bottom to add more distance from GND vias. Also widened the
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T junction to one of the via to 0.6 mm
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### Notes
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* Adding series resistor for `gps_reset_n` and `gps_pps` was considered, but deemed not necessary.
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* Traces are short, always close to ground plane and we have no strong RF/EMI emitter onboard.
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* `gps_pps` is generated by the module itself, so any fast edge is coming from the module.
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* `gps_reset_n` is static.
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* Adding a capacitor between `tx_hi` and `tx_lo` (after the series resistor) was also an option.
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Testing showed it didn't really change / improve the pulse shape and simulation showed increased
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peak current (and thus stress on the UP5k drivers). I considered adding a DNP footprint but area
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was a bit cramped and some more work would have been needed for something that would most likely
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stay unpopulated.
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