From 5774b03e60e4d6d48cb4930844e646cf74192c05 Mon Sep 17 00:00:00 2001 From: cah Date: Mon, 30 Mar 2026 22:03:08 -0600 Subject: [PATCH] docs: fix BOM errors found in adversarial review Showstoppers fixed: - Crystal (ABM8, passive) -> SiT8008 active CMOS oscillator (Caravel has no on-chip crystal driver) - FT232RL (NRND) -> CH340C (active production, built-in osc) - ADCMP607: "3.5 GHz LVPECL" -> "800 ps CML" (per datasheet) - EMCO Q02-5 (200V!) -> LT3482 boost converter (~30V for SiPM) High-severity fixed: - "85 mW total" -> "~100 mW (86 mW decoder + ~15 mW Caravel)" - AP2112K 1.8V (600mA marginal) -> AMS1117-1.8 (1A headroom) - BAE GMAPD: added availability caveat (defense/ITAR-restricted) - "ATI DAPD" -> "Amplification Technologies DAPD" (correct name) - Added ID Quantique ID230 as commercial 1550nm alternative Updated all BOM totals and cost summary to match. Co-Authored-By: Claude Opus 4.6 (1M context) --- README.md | 75 +++++++++++++++++++++++++++++-------------------------- 1 file changed, 39 insertions(+), 36 deletions(-) diff --git a/README.md b/README.md index b6deb44..08a782f 100644 --- a/README.md +++ b/README.md @@ -10,7 +10,7 @@ A soft-input LDPC decoder ASIC targeting the ChipFoundry chipIgnite shuttle (Sky ### Free-Space Optical Downlinks (CubeSat, UAV-to-Ground) -Low-Earth orbit CubeSat optical downlinks operate at 1-5 photons per slot due to extreme path loss over 400-2000 km. The rate 1/8 code provides 8x redundancy, enabling reliable communication well below 1 photon per information bit. At 85 mW total power (decoder + Caravel), the ASIC fits CubeSat power budgets (typically 1-5 W total spacecraft). The 2.5 Mbps decoded throughput matches typical CubeSat downlink requirements. The same decoder serves UAV-to-ground and building-to-building free-space optical (FSO) links where atmospheric turbulence and beam wander reduce received photon counts to similar levels. +Low-Earth orbit CubeSat optical downlinks operate at 1-5 photons per slot due to extreme path loss over 400-2000 km. The rate 1/8 code provides 8x redundancy, enabling reliable communication well below 1 photon per information bit. At ~100 mW total power (86 mW decoder + ~15 mW Caravel management core), the ASIC fits within CubeSat payload power budgets (typically 1-5 W allocated to communications). The 2.5 Mbps decoded throughput matches typical CubeSat downlink requirements. The same decoder serves UAV-to-ground and building-to-building free-space optical (FSO) links where atmospheric turbulence and beam wander reduce received photon counts to similar levels. ### Underwater Optical Modems @@ -108,24 +108,25 @@ A minimal breakout board for silicon bring-up and firmware demo, designed for im ``` USB-C | - +-----v------+ - | FT232RL | +--------+ - | USB-UART |---->| SPI | - +-----+------+ | Flash | - | | W25Q32 | - +-----v------+ +---+----+ - | AP2112K | | - | 3.3V LDO | +----v-----------+ - +-----+------+ | | - | | Caravel | - +-----v------+ | QFN-64 | - | AP2112K | | (LDPC decoder | - | 1.8V LDO |-->| inside) | - +-----+------+ | | - | +----+-----------+ - +-----v------+ | - | 25 MHz XTAL|--------+ - +------------+ + +-----v------+ +--------+ + | CH340C | | SPI | + | USB-UART |---->| Flash | + +-----+------+ | W25Q32 | + | +---+----+ + +-----v------+ | + | AP2112K | +----v-----------+ + | 3.3V LDO | | | + +-----+------+ | Caravel | + | | QFN-64 | + +-----v------+ | (LDPC decoder | + | AMS1117 | | inside) | + | 1.8V 1A |-->| | + +-----+------+ +----+-----------+ + | | + +-----v-----------+ | + | SiT8008 25 MHz |--+ + | CMOS oscillator | + +-------------------+ Reset btn, Power LED, 2x Status LEDs ``` @@ -144,10 +145,10 @@ A minimal breakout board for silicon bring-up and firmware demo, designed for im | Component | Part | Qty | Est. Cost | |-----------|------|-----|-----------| -| 25 MHz crystal oscillator | ABM8-25.000MHZ-B2-T | 1 | $0.50 | +| 25 MHz CMOS oscillator | SiT8008BI-73-25E | 1 | $0.90 | | 3.3V LDO regulator | AP2112K-3.3TRG1 | 1 | $0.35 | -| 1.8V LDO regulator | AP2112K-1.8TRG1 | 1 | $0.35 | -| USB-UART bridge | FT232RL | 1 | $4.50 | +| 1.8V LDO regulator (1A) | AMS1117-1.8 | 1 | $0.25 | +| USB-UART bridge | CH340C | 1 | $0.50 | | SPI flash (32 Mbit) | W25Q32JVSSIQ | 1 | $0.65 | | USB-C connector | USB4110-GF-A | 1 | $0.60 | | Decoupling caps (100nF) | CL05B104KO5NNNC | 12 | $0.60 | @@ -155,9 +156,9 @@ A minimal breakout board for silicon bring-up and firmware demo, designed for im | Reset button | PTS645SM43SMTR92 | 1 | $0.15 | | LEDs + resistors | -- | 5 | $0.50 | | PCB fabrication (qty 5) | JLCPCB 2-layer FR4 | 1 | $2.00 | -| **Total (excl. Caravel chip)** | | | **~$11** | +| **Total (excl. Caravel chip)** | | | **~$8** | -All components are commodity parts available from Digi-Key and LCSC with no long-lead items. Board is designed for hand assembly or JLCPCB SMT service (~$30-50 assembled in qty 5). +All components are commodity parts available from Digi-Key and LCSC with no long-lead items. The CH340C includes a built-in oscillator (no external crystal needed). The AMS1117-1.8 provides 1A output current for headroom on the 1.8V core supply. Board is designed for hand assembly or JLCPCB SMT service (~$25-40 assembled in qty 5). ### Optical Frontend -- Part B (Reference Design) @@ -169,7 +170,7 @@ A reference design for the optical receiver frontend, sharing the same PCB as Pa +----v--------+ +-------------+ +----------+ | GMAPD/SiPM |---->| TIA |---->| Fast | | Detector | | AD8015 | | Comp. | - | (HV bias) | | 240 MHz BW | | ADCMP607 | + | (bias ~30V) | | 240 MHz BW | | ADCMP607 | +----+---------+ +-------------+ +----+-----+ | | +----v--------+ +----v-----+ @@ -187,9 +188,9 @@ A reference design for the optical receiver frontend, sharing the same PCB as Pa **Part B signal chain:** 1. **Detector**: Geiger-mode APD (BAE Systems GMAPD) or SiPM stand-in (ON Semi C-Series MicroFC-60035) for bench demos 2. **TIA**: AD8015 transimpedance amplifier (240 MHz bandwidth, 10 kOhm gain) -3. **Comparator**: ADCMP607 (3.5 GHz bandwidth, LVPECL output) converts analog pulse to digital timestamp +3. **Comparator**: ADCMP607 (800 ps propagation delay, CML output) converts analog pulse to digital timestamp 4. **LLR computation**: RP2040 MCU counts photon arrivals per slot, computes Poisson-model LLRs, writes to Caravel via SPI/UART -5. **HV bias**: Isolated DC-DC for detector bias (20-70V depending on detector) +5. **HV bias**: Isolated DC-DC boost converter for SiPM bias (~25-30V) **Bill of Materials (Part B additional):** @@ -199,10 +200,10 @@ A reference design for the optical receiver frontend, sharing the same PCB as Pa | Transimpedance amplifier | AD8015ARZ | 1 | $8 | | Fast comparator | ADCMP607BCPZ | 1 | $6 | | Companion MCU | RP2040 | 1 | $1 | -| HV bias module | EMCO Q02-5 | 1 | $15 | +| SiPM bias supply (30V boost) | LT3482 + passives | 1 | $8 | | SMA connector (ext. clock) | SMA-J-P-H-ST-EM1 | 1 | $1 | | Passives + connectors | -- | ~20 | $5 | -| **Part B additional total** | | | **~$66** | +| **Part B additional total** | | | **~$59** | ### Full Bench Demo System @@ -226,8 +227,10 @@ The Part B SiPM frontend is designed for low-cost bench demos. For operational d | Detector | Type | Wavelength | Key Advantage | Typical Use | |----------|------|------------|---------------|-------------| -| BAE Systems GMAPD | Geiger-mode APD array | 1064 / 1550 nm | High sensitivity, proven in NASA/DARPA programs | Deep-space optical, LIDAR | -| ATI DAPD | Discrete amplification PD | 1550 nm | Photon-number-resolving (PNR) | Quantum optics, high-fidelity optical comm | +| GMAPD array (MIT Lincoln Lab / BAE) | Geiger-mode APD array | 1064 / 1550 nm | High sensitivity, proven in NASA/DARPA programs | Deep-space optical, LIDAR | +| Amplification Technologies DAPD | Discrete amplification photon detector | 1550 nm | Photon-number-resolving (PNR) | Quantum optics, high-fidelity optical comm | + +**Availability note:** GMAPD arrays are primarily developed under government contracts (MIT Lincoln Laboratory, BAE Systems) and are not commercial off-the-shelf parts -- procurement typically requires a defense or research relationship. The Amplification Technologies DAPD is available commercially for research applications. For non-restricted deployments, InGaAs SPADs (e.g., ID Quantique ID230) provide single-photon sensitivity at 1550 nm as a commercially available alternative. **Why photon-number resolution matters for this decoder:** @@ -237,7 +240,7 @@ The SiPM and GMAPD in Geiger mode produce binary outputs (click / no-click). The LLR_binary = log(P(click | bit=1) / P(click | bit=0)) ``` -A photon-number-resolving detector like the ATI DAPD reports the actual photon count k per slot. The LLR uses the full Poisson probability mass function: +A photon-number-resolving detector like the Amplification Technologies DAPD reports the actual photon count k per slot. The LLR uses the full Poisson probability mass function: ``` LLR_PNR(k) = (lambda_s) - k * ln((lambda_s + lambda_b) / lambda_b) @@ -256,11 +259,11 @@ The electrical interface is identical to Part B: the detector's analog output fe | Item | Est. Cost | Status | |------|-----------|--------| | chipIgnite shuttle | Contest-covered | GDSII submitted | -| Part A breakout board (assembled qty 5) | $30-50 | KiCad design complete, fab-ready on silicon return | -| Part B optical frontend (additional) | ~$66 | Schematic complete, components specified (DNP) | +| Part A breakout board (assembled qty 5) | $25-40 | KiCad design complete, fab-ready on silicon return | +| Part B optical frontend (additional) | ~$59 | Schematic complete, components specified (DNP) | | Full demo system (TX + RX + optics) | $150-250 | Documented, post-silicon integration | | Advanced frontend (GMAPD or DAPD) | $5K-15K | Integration path documented, no ASIC changes needed | -| **Minimum viable demo** | **$30-50** | **Buildable immediately on silicon return** | +| **Minimum viable demo** | **$25-40** | **Buildable immediately on silicon return** | ## Verification Status @@ -378,7 +381,7 @@ GDSII layout viewable in KLayout. All DRC checks clean (Magic and KLayout). LVS **Phase 2: Silicon Bring-Up (Oct/Nov 2026, on silicon return)** - Part A breakout board ordered from JLCPCB (~$2/board, 5-unit MOQ) -- Components ordered from Digi-Key (~$11 BOM per board) +- Components ordered from Digi-Key/LCSC (~$8 BOM per board) - Board assembly (hand-solder or JLCPCB SMT assembly) - First silicon bring-up: VERSION register read over UART, firmware demo execution - Measure real-silicon decode latency and power, compare to simulation predictions