USTSIPM01 — Silicon photomultiplier (SiPM) interface module

Complete analog front‑end for Silicon Photomultipliers (SiPM). The module provides resistor-configurable high‑voltage bias for the SiPM sensor and a low‑noise, wideband readout stage suitable for timing and amplitude measurements.

Features

• Footprint for onsemi MicroFC‑60035‑SMT SiPM (6×6 mm, 35 µm microcells).
• On‑board high‑voltage boost converter MAX5026 generating the SiPM bias from the +5 V rail.
• Precision feedback network with design equation Vout = 1.25 V × (1 + R2/R3); default configuration targets to 31.7 V bias.
• Low‑noise wideband amplifier stage OPA836 for SiPM signal readout.
• Pin-header connector for lab bring‑up and diagnostics.

Block Diagram

flowchart LR
    V["3V6"] -->|Bias supply| MAX5026["MAX5026 Boost"]
    MAX5026 -->|VBIAS 25-32 V| SiPM["SiPM MicroFC-60035"]
    SiPM -->|A| OPA836["OPA836 Readout"]
    OPA836 --> OUT["OUT"]
    V33["+3.3 V"] --> OPA836

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Electrical Characteristics (module)

• Supply rails: +3.6 V (bias converter), +3.3 V (analog stage).
• SiPM bias range: designable in ~25–32 V via resistor ratio (see below). Default assembly ≈ 31.7 V.
• Output: single‑ended, wideband path suitable for 50 Ω instrumentation (use external 50 Ω termination at scope/DAQ as required).

Note (SiPM operating point): The sensor is biased at Vout = VBR + VOV, where VBR is the device’s breakdown voltage and VOV is the selected overvoltage. Typical recommended VOV = 1…5 V. Temperature coefficient of VBR ≈ +21.5 mV/°C (adjust bias accordingly).

Bias Network Design

The MAX5026 feedback follows:

Vout = 1.25 V × (1 + R2/R3)

Default population (R2 = 3.9 MΩ, R3 = 160 kΩ) yields:

Vout ≈ 1.25 × (1 + 3.9M/160k) ≈ 31.7 V

Example design for MicroFC‑60035 with typical VBR ≈ 24.7 V:

• For VOV = 3.0 V → target Vout ≈ 27.7 V.
• Choose standard values to satisfy 1.25 × (1 + R2/R3) ≈ 27.7. For example, R3 = 160 kΩ, R2 ≈ 3.394 MΩ (use 3.40 MΩ or parallel combination). Verify with measurement on the assembled board.

Keep the feedback resistors in the MΩ range to minimize divider current, and place them tight to the FB node. Use a low‑leakage layout around FB. Treat the SiPM and the module as ESD‑sensitive.

Operating Guidance

• Start at low overvoltage (e.g., +1…2 V above the measured VBR) and increase gradually while monitoring dark count and pulse shape.
• Observe the maximum average current rating of the chosen sensor (for 6×6 mm devices typically tens of mA). Avoid saturating the device with continuous high optical flux.

Changeable Parameters

• SiPM bias (R2/R3): select to set the required overvoltage window for the specific sensor lot and operating temperature.
• OPA836 gain (R10/R12): non‑inverting stage; A_v = 1 + R10/R12. Default R10 = 12 kΩ, R12 = 1 kΩ → A_v ≈ 13 V/V (~22.3 dB). Adjust these resistors to set the desired voltage gain. (See schematic).