Pass 148

PDLVDS-RX — photodiode LVDS receiver

Clean-room receiver for the Miniscope Zero optical uplink: Excelitas C30737LH Si APD → OPA657 TIA → LMH7220 comparator (LVDS out, DAC-set threshold) → ADN2813 CDR → STM32H723 + USB3300 USB-HS. Design target: 50 Mbps line rate, 8b/10b (40 Mbps payload); the paper's mode: 8 Mbps Manchester (16 Mbaud), as transmitted. LT3757 flyback APD bias 150–420 V. USB-C powered; verify on any laptop over USB, no FPGA attached.

2026-11-06 01:46 PST (2026-11-06T09:46:30Z UTC) · commit bbb5dd6 (bbb5dd6f7feb79646a227933fdb7ac9fb2345904)

ADOPTED

East edge cleared: the J2 CDR pair escape reworked. Diagnosis chain: the pair (J2.5/6 pads at x=98.08) escaped east into a shared channel at x=99.375 whose fanout topology forced the heal to re-lay it identically after every rip (three attempts); the sacrificial-fence mechanism proved lossy on this stack – a no-op heal run drops fence tracks layer-specifically (In2 loses the out-of-outline column at save, F.Cu loses tracks through save_checkpoint) and routed runs rename survivors to GND (three 123 mm GND-named fence columns found by geometry census and deleted by exact geometry; committed exp177 verified phantom-free by the same census). Working recipe: DENSE fence (0.3 mm pitch, 28 tracks, x 98.9..100.7 full height), wide rip of both pair nets east of x=96.5 (46+28 segments), heal (CLKP took a real interior route: 28 s, 3 vias), fence removal by name AND geometry, then a zone refill (the heal checkpoint refills with the fence still on; without a post-removal refill the F.Cu GND pour keeps fence-shaped slots and reads +1 unconnected island). KiCad DRC referee against committed exp177 (217/44): violations 217 -> 209, copper_edge_clearance 33 -> 20 with ZERO items east of x=98 remaining (the +3V3D east trunk and the whole CDR_CLKP/CLKN east run are gone), clearance 35, shorting 0, unconnected 44 UNCHANGED after the refill. Remaining edge items are exactly the J1 south field (20, placement-decision class). New CLKN path passes close to SWCLK on In2 (one clearance item, named for the clearance campaign).