# Readout Circuit ## Description Four-layer cryogenic DC-coupled SNSPD readout amplifier based on the TI OPA855, targeting approximately 16.7 dB gain and multi-gigahertz bandwidth at 40 K. ## Project Details - **Owner:** anicvedi - **Created:** 8/20/2026 - **Last Updated:** 8/27/2026 - **Visibility:** Public - **Operating Voltage:** 4.9V - **Implementation Details:** 4-layer FR4, OPA855 WSON-8, DC-coupled SNSPD readout - **Domain:** Cryogenic instrumentation - **Operating Temperature:** 40K - **Copies:** 1 ## Key Components ### J1 — 132255-11 - Role Details: SNSPD_BIAS edge-launch SMA input; center pin feeds R5 100k and shields remain GND - Datasheet URL: https://www.amphenolrf.com/en-us/assets/file/4065786425/ - Manufacturer Name: Amphenol RF - Functional Group: SNSPD Bias - Role: Biasing - Connector Type: RF / Coaxial Connectors - Part Type: Connector - Manufacturer Part Number: 132255-11 - License: https://creativecommons.org/licenses/by/4.0/ **Pins:** - 1 [pin 1] - 2 [pin 2] - 3 [pin 3] - 4 [pin 4] - 5 [pin 5] ### J2 — 132255-11 - Part Type: Connector - Connector Type: RF / Coaxial Connectors - Role Details: VOUT 50 ohm coax interface - Manufacturer Name: Amphenol RF - License: https://creativecommons.org/licenses/by/4.0/ - Manufacturer Part Number: 132255-11 - Functional Group: Output Interface - Datasheet URL: https://www.amphenolrf.com/en-us/assets/file/4065786425/ - Role: Coupling **Pins:** - 1 [pin 1] - 2 [pin 2] - 3 [pin 3] - 4 [pin 4] - 5 [pin 5] ### J3 — 132255-11 - Role Details: V+S_RAW edge-launch SMA supply input; center pin to V+S_RAW and shield pins to GND - Functional Group: Positive Supply Input - Datasheet URL: https://www.amphenolrf.com/en-us/assets/file/4065786425/ - Role: Power Input - Manufacturer Part Number: 132255-11 - License: https://creativecommons.org/licenses/by/4.0/ - Manufacturer Name: Amphenol RF - Connector Type: RF / Coaxial Connectors - Part Type: Connector **Pins:** - 1 [pin 1] - 2 [pin 2] - 3 [pin 3] - 4 [pin 4] - 5 [pin 5] ### J4 — 132255-11 - Manufacturer Name: Amphenol RF - Part Type: Connector - Connector Type: RF / Coaxial Connectors - Manufacturer Part Number: 132255-11 - License: https://creativecommons.org/licenses/by/4.0/ - Functional Group: Negative Supply Input - Role: Power Input - Role Details: V-S_RAW edge-launch SMA supply input; center pin to V-S_RAW and shield pins to GND - Datasheet URL: https://www.amphenolrf.com/en-us/assets/file/4065786425/ **Pins:** - 1 [pin 1] - 2 [pin 2] - 3 [pin 3] - 4 [pin 4] - 5 [pin 5] ### TP1 — S2761-46R - Role Details: V+_FILT bring-up access - Part Type: Test Point - Manufacturer Name: Harwin Inc. - Datasheet URL: https://www.harwin.com/api/download/datasheet/S2761-46R - Role: Sensing (Shunt) - License: https://creativecommons.org/licenses/by/4.0/ - Manufacturer Part Number: S2761-46R - Functional Group: Bring-up Test Points **Pins:** - ~ [pin 1] ### TP2 — S2761-46R - Datasheet URL: https://www.harwin.com/api/download/datasheet/S2761-46R - Role: Sensing (Shunt) - Manufacturer Name: Harwin Inc. - Part Type: Test Point - Role Details: V-_FILT bring-up access - Functional Group: Bring-up Test Points - Manufacturer Part Number: S2761-46R - License: https://creativecommons.org/licenses/by/4.0/ **Pins:** - ~ [pin 1] ### TP3 — S2761-46R - Manufacturer Name: Harwin Inc. - Part Type: Test Point - Functional Group: Bring-up Test Points - Datasheet URL: https://www.harwin.com/api/download/datasheet/S2761-46R - Role Details: GND bring-up access - License: https://creativecommons.org/licenses/by/4.0/ - Role: Sensing (Shunt) - Manufacturer Part Number: S2761-46R **Pins:** - ~ [pin 1] ### U1 — OPA855IDSGT - Manufacturer Name: TI(德州仪器) - Role: Amplification - Manufacturer Part Number: OPA855IDSGT - Part Type: Operational Amplifier - Role Details: OPA855 datasheet total supply max = 5.5 V (e.g. ±2.75 V). ±4.9 V is an experimental cryogenic over-voltage reported by the reference paper; do not apply at room temperature and use only under controlled research conditions. - Package or Case Code: WSON-8_L2.0-W2.0-P0.50-TL-EP - Functional Group: Amplifier Core - JLCPCB Part Class: Extended Part - LCSC Part Number: C2870367 - Datasheet URL: https://www.ti.com/lit/ds/symlink/opa855.pdf **Pins:** - ~{PD} [pin 8] - EP [pin 9] - FB [pin 1] - IN- [pin 3] - IN+ [pin 4] - NC [pin 2] - OUT [pin 6] - VS- [pin 5] - VS+ [pin 7] *The full schematic, PCB layout, bill of materials, and interactive design are available at [https://www.flux.ai/anicvedi/readout-circuit~bj](https://www.flux.ai/anicvedi/readout-circuit~bj).* --- *Generated from [https://www.flux.ai/anicvedi/readout-circuit~bj](https://www.flux.ai/anicvedi/readout-circuit~bj)*