Pass 150

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 03:33 PST (2026-11-06T11:33:43Z UTC) · commit 04b5078 (04b507822882d7c63c65482672b053b5d1c78e60)

ADOPTED

First re-route of the re-placed board (exp179, pass 149): three heal campaigns over the bare board (residue/stuck set first while the field was empty, then two full sweeps resumed across a VM restart from the 60-group checkpoint). 234 groups connected in total. KiCad DRC referee against the bare exp179 (154 violations / 303 unconnected): violations 167 (silk_overlap/silk_over_copper 148 – the designator-text class the re-placement created, tail work; copper_edge_clearance 7; shorting_items 6, named below; CLEARANCE 0 and DANGLING 0 – the heal lays are clean), unconnected 303 -> 82. Residue by net (DRC items): GND 56 (never healed – the pour alone strands pads/islands; gets its own heal next), +VA 18 (the one total failure: every group exhausted the search cap; two clusters 12 mm apart around U13/front-end, mechanism to be diagnosed with the board rendered), TIA_OUT 8 (front-end enclosure: U1.6 and C5.1 each failed after ~146 s searches), +3V3A 4 (U7.6/U7.25 sealed pads), APD_A 4 (D1.2/4/6 sealed under the shield can), DP_CON 4 (J1.B6), I2C_SDA 4, +3V3D 2 (U11.14), +3V3D_CDR 2 (U4.12), APD_K 2 (D1.5), CAP_CLK 2 + CAP_DATA 2 (U5-U6 corridor), plus the sealed-pad set (U7 ULPI ring, U4.4/22/28, SWCLK, C23.1 PHY_1V8A). Next: hand-stub fanout for the sealed pads (hw/hand_stub.py exists for exactly this), GND heal, shorts prune, then the residue diagnoses. Placement dividend already visible: +5V, the ULPI bus’s U6 side, both CDR pairs and the HV chain connected in seconds-to-minutes where the old placement ground for hours.