Current intended operating rails: +2.5 V and −2.5 V
RF traces:VIN and VOUT, nominally 0.180 mm on L1, referenced to L2 GND
Latest reported routing status: zero airwires, dangling traces, and active ERC/DRC errors
Important hold points
OPA855 decoupling is unresolved.
The previous supply capacitors were removed. Exact local bypass requirements must be verified directly from the OPA855 device datasheet before release. A multi-GHz amplifier should not be fabricated without an approved supply-decoupling implementation.
Stackup is provisional.
The current “PCBWay Custom” stackup is not an approved PCB Power India stackup. Obtain:
exact four-layer construction
finished copper thicknesses
L1–L2 dielectric thickness and Dk
recommended L1 width for 50 Ω
impedance tolerance and coupon/test availability
SNSPD footprint remains provisional.
Confirm:
real die dimensions and thickness
exact bond-pad coordinates and metallurgy
signal and return pad locations
backside electrical requirements
approved die-attach material
Wire-bond finish is unresolved.
The PCB pads are exposed top-copper lands with solder paste suppressed. Select ENIG, ENEPIG, or soft gold only after agreement between the SNSPD supplier, bonding laboratory, and PCB Power.
OptiCool mechanics remain provisional.
Board fits the nominal pod envelope in 2D.
Mounting-hole coordinates are not verified.
RF/DC feedthrough mating geometry and cable clearance are not confirmed.
Do not add or drill mounting holes from assumed dimensions.
Cryogenic qualification is not established.
OPA855 operation on this exact PCB at 4 K is unverified.
L1 inductance, Q, self-resonance, and DC resistance at 4 K are unverified.
Connector, laminate, solder, adhesive, and capacitor behavior at 4 K require validation.
Results from the referenced paper do not automatically qualify this exact BOM or thermal arrangement.
Simulation status
Behavioral U1 transient:
J1 = 1.5 V
nominal bias = 15 µA
switching threshold = 20 µA
J3/J4 = ±2.5 V
measured transient gain ≈ 7.025 V/V
This was not a verbatim TI OPA855 macro-model simulation.
The supplied TI .sub file is valid, but the built-in simulator cannot access uploaded include files.
The photon event was represented as an electrical hotspot surrogate, not an optical-field simulation.
Required release sequence
Verify the OPA855 device-datasheet bypass network and restore the required local components.
Obtain and apply PCB Power’s production stackup.
Recalculate/tune VIN and VOUT for 50 Ω.
Confirm SNSPD and wire-bond process data.
Verify OptiCool mounting and connector geometry.
Run fresh ERC, DRC, airwire, return-path, keepout, and Gerber inspections.
Generate new Gerbers, drill files, IPC-D-356, BOM, and pick-and-place files.
Submit to PCB Power for CAM/DFM review.
Order a small bare-board/prototype quantity first.
Do not use earlier manufacturing exports: they predate major changes including the two-pad SNSPD footprint, routing updates, capacitor removal, L1 addition, and R3 output load.
Hi. The PCB is currently at the engineering-prototype stage, with supply decoupling, PCB Power stackup, SNSPD bonding requirements, and OptiCool mechanics still to be finalized before manufacturing release.
OPA855: ±4.9 V is experimental cryogenic operation only; total supply exceeds the 5.5 V datasheet absolute maximum. NEVER apply ±4.9 V at room temperature.
SNSPD bias: use J1 SNSPD_BIAS through R5=100 kΩ; target about 1.4–1.5 V for approximately 14–15 µA (Isw=16 µA), not 2 V/100 kΩ.
R4
Resistance
50Ω
R2
Resistance
75Ω
R5
Resistance
100kΩ
U1
TP3
TP1
TP2
C1
J4
J3
J2
J1
Full PCB Transient Simulation
Purpose
Transient-only verification of the complete current readout topology: detector bias at J1, OPA855 supply entries J3/J4, and output at J2.
Datasheet-compliant supply condition
J3 / V+S_RAW: +2.5 V
J4 / V-S_RAW: −2.5 V
Total OPA855 supply: 5.0 V
This uses the OPA855 datasheet nominal total supply value and remains inside its 3.3–5.25 V recommended operating range. The previous ±5 V condition is not valid for normal datasheet operation.
Detector-bias and event setup
J1 / SNSPD_BIAS: +0.75 V
R5: 100 kΩ (installed)
Nominal pre-event bias: approximately 7.5 µA
Photon-equivalent event: 2 ps trigger at 20 ns in a backend-compatible SNSPD switching surrogate.
The physical photon is top incident on the SNSPD die. Its electrothermal conversion is represented electrically by the trigger only. This bias is a conservative starting point for the uploaded model defaults—not a calibrated operating point for the actual detector.
Included PCB circuit
DIE1 detector surrogate, R4=50 Ω, R5=100 kΩ
U1 non-inverting behavioral amplifier, feedback R1=453 Ω and R2=75 Ω
The measured gain matches the populated feedback network: 1 + 453/75 = 7.04 V/V. The 2.64 mV output is far inside the ±2.5 V rails; no clipping occurred.
Waveform
Full PCB transient
Waveform data CSV
Loading CSV...
Model limitation
The run includes the complete PCB topology and real populated passive values. However, the detector event is a backend-compatible electrical surrogate and U1 is a behavioral amplifier, because the exact uploaded thermal-port SNSPD model and an OPA855 macro-model require the separate LTspice workflow. Do not interpret pulse height or recovery as calibrated device performance.