• Completed — OPA855 gain network preserved: R1 remains 453 Ω from VOUT/FB to IN− and R2 remains 75 Ω from IN− to GND, for approximately 7.04 V/V (16.95 dB).
• Completed — local supply decoupling: both OPA855 supply rails now have high-frequency and local bulk bypassing.
• Completed — resistive SNSPD bias input: J1 is now the detector-bias connector and feeds VIN through R5 = 100 kΩ.
• Completed — output load correction: the onboard R3 = 200 Ω VOUT shunt was removed; J2 remains the 50 Ω instrument/coax output.
• Completed — PCB cleanup/routing: obsolete VIN/VOUT branches were removed and the revised nets were rerouted with no remaining airwires or dangling traces.
• Completed — DIE1 mechanics preserved: the 6.0 × 6.0 mm body, centered 7.0 × 7.0 mm mounting area, bond-pad banks, and position were not altered.

• R3 = 200 Ω, formerly from VOUT to GND.
• Its PCB branch and the former J1-to-VIN copper branch were removed with the obsolete routing.

Text
J1 center (SNSPD_BIAS) ── R5 100 kΩ ── VIN/readout node
                                            ├── DIE1 P1 (SPICE drain)
                                            ├── U1 IN+
                                            └── R4 50 Ω ── GND

DIE1 P2 (SPICE source) ── GND

U1 OUT/FB ── VOUT ── J2 center
       └── R1 453 Ω ── IN− ── R2 75 Ω ── GND

• PD low disables the amplifier and high enables normal operation, so the existing PD-to-V+S_RAW connection was preserved.
• The exposed pad is to be tied to VS−, so the existing EP-to-V-S_RAW connection was preserved.
• The supply pins require close high-frequency bypass capacitors and also recommend larger 2.2–6.8 µF local capacitors farther from the device.

• ±4.9 V is experimental cryogenic operation only. It exceeds the OPA855 5.5 V total-supply absolute maximum and must never be applied at room temperature.
• Use J1 with an adjustable source around 1.4–1.5 V through R5 = 100 kΩ to target approximately 14–15 µA for a detector with Isw = 16 µA.
• Do not use the reference simulation's 2 V / 100 kΩ setting as the normal operating point; it approaches 20 µA and exceeds the stated switching-current target.

• C1 and C2 were placed near U1's VS+ and VS− pads with short, wide rail connections and nearby ground returns.
• C3 and C4 were placed farther from U1 and connected with 0.5 mm rail traces.
• R5 was placed immediately left of the DIE1 working envelope, close to P1, while preserving the detector geometry.
• VIN and VOUT were rerouted without the former connector/load stubs.
• Deterministic U1 neckdowns were generated before rerouting.

• Airwires: 0
• Dangling traces: 0
• Overlapping copper/traces: no open findings
• Critical ERC/DRC findings: none
• Intentionally remaining manufacturing warning: DIE1 has no manufacturer part number because it is a custom assumed placeholder.
• Intentionally remaining physical warning: the DIE1 bond-pad geometry is still provisional and not fabrication-qualified without detector-maker and bonding-lab data.