31 Mar
2025
31 Mar
'25
1:01 p.m.
On 3/30/25 6:44 PM, Martin Bishop wrote:
Your driver design sketches and comments are
substantially on the money. Thank you for making them public. However, an effective
implementation in discrete components would not be "tiny" - even with 0402
passives and a pick / place machine on the case.
No, not tiny. With the BGA parts of the FPGA and DDR3 SDRAM, I'd
already made the choice that this board would have to be commercially
assembled so smaller parts were acceptable. Even so, at one point I
mocked it up just to see if it would fit with SOT-23 and 0603 parts and
it did, just barely, across a double-height QBUS board. That was one of
my simpler designs for this, though. So dunno. If you can lay out the
circuit to drive two bus lines in a chain of components that's only one
SOT-23 wide, then I think it fits. It might stretch up the board a
ways, but I have room in that direction.
Perhaps someday, someone will do a Q/U driver on a
multi project wafer - or is that unafordable. Or, to fly another kite - what about FPAA
(Field Programmable Analog Array) components ?
I hadn't thought about those multi-project wafers. Don't know if that'd
make sense. I keep hoping that one day soon we'll start to see
hobbyist-level 3d printing of ICs. Maybe only 1µm feature size or even
larger but think what people would do with that. Not out there yet though.
Regarding comparators, as receivers, the TLV3501 (for
example) is a 5v / 5 ns part - add hysteresis and set the H/L thresholds using resistors.
Certainly receives OC signals for me.
Yup, that's the sort of part I was thinking of. I'd used the MAX9107
but the TI part is even faster. One thing I could never find was a
comparator that was both fast and had a OC/OD output. Or one that ran on
3.3V so it could drive the FPGA directly but was rated for higher
voltages than Vcc on the inputs.
Should you make further progress very interested to
hear of it
I'm not sure where I'm going to go with these ideas but if I do
anything, I'll be sure to let people know.
Dave