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) <noreply@anthropic.com>
This commit is contained in:
73
README.md
73
README.md
@@ -10,7 +10,7 @@ A soft-input LDPC decoder ASIC targeting the ChipFoundry chipIgnite shuttle (Sky
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### Free-Space Optical Downlinks (CubeSat, UAV-to-Ground)
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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.
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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.
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### Underwater Optical Modems
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@@ -108,24 +108,25 @@ A minimal breakout board for silicon bring-up and firmware demo, designed for im
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```
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USB-C
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+-----v------+
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| FT232RL | +--------+
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| USB-UART |---->| SPI |
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+-----+------+ | Flash |
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| | W25Q32 |
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+-----v------+ +---+----+
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| AP2112K | |
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| 3.3V LDO | +----v-----------+
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+-----+------+ | |
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| | Caravel |
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+-----v------+ | QFN-64 |
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| AP2112K | | (LDPC decoder |
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| 1.8V LDO |-->| inside) |
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+-----+------+ | |
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| +----+-----------+
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+-----v------+ +--------+
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| CH340C | | SPI |
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| USB-UART |---->| Flash |
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+-----+------+ | W25Q32 |
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| +---+----+
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+-----v------+ |
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| 25 MHz XTAL|--------+
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+------------+
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| AP2112K | +----v-----------+
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| 3.3V LDO | | |
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+-----+------+ | Caravel |
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| | QFN-64 |
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+-----v------+ | (LDPC decoder |
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| AMS1117 | | inside) |
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| 1.8V 1A |-->| |
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+-----+------+ +----+-----------+
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| |
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+-----v-----------+ |
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| SiT8008 25 MHz |--+
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| CMOS oscillator |
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+-------------------+
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Reset btn, Power LED, 2x Status LEDs
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```
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@@ -144,10 +145,10 @@ A minimal breakout board for silicon bring-up and firmware demo, designed for im
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| Component | Part | Qty | Est. Cost |
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|-----------|------|-----|-----------|
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| 25 MHz crystal oscillator | ABM8-25.000MHZ-B2-T | 1 | $0.50 |
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| 25 MHz CMOS oscillator | SiT8008BI-73-25E | 1 | $0.90 |
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| 3.3V LDO regulator | AP2112K-3.3TRG1 | 1 | $0.35 |
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| 1.8V LDO regulator | AP2112K-1.8TRG1 | 1 | $0.35 |
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| USB-UART bridge | FT232RL | 1 | $4.50 |
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| 1.8V LDO regulator (1A) | AMS1117-1.8 | 1 | $0.25 |
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| USB-UART bridge | CH340C | 1 | $0.50 |
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| SPI flash (32 Mbit) | W25Q32JVSSIQ | 1 | $0.65 |
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| USB-C connector | USB4110-GF-A | 1 | $0.60 |
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| Decoupling caps (100nF) | CL05B104KO5NNNC | 12 | $0.60 |
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@@ -155,9 +156,9 @@ A minimal breakout board for silicon bring-up and firmware demo, designed for im
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| Reset button | PTS645SM43SMTR92 | 1 | $0.15 |
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| LEDs + resistors | -- | 5 | $0.50 |
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| PCB fabrication (qty 5) | JLCPCB 2-layer FR4 | 1 | $2.00 |
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| **Total (excl. Caravel chip)** | | | **~$11** |
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| **Total (excl. Caravel chip)** | | | **~$8** |
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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).
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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).
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### Optical Frontend -- Part B (Reference Design)
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@@ -169,7 +170,7 @@ A reference design for the optical receiver frontend, sharing the same PCB as Pa
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+----v--------+ +-------------+ +----------+
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| GMAPD/SiPM |---->| TIA |---->| Fast |
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| Detector | | AD8015 | | Comp. |
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| (HV bias) | | 240 MHz BW | | ADCMP607 |
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| (bias ~30V) | | 240 MHz BW | | ADCMP607 |
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+----+---------+ +-------------+ +----+-----+
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| |
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+----v--------+ +----v-----+
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@@ -187,9 +188,9 @@ A reference design for the optical receiver frontend, sharing the same PCB as Pa
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**Part B signal chain:**
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1. **Detector**: Geiger-mode APD (BAE Systems GMAPD) or SiPM stand-in (ON Semi C-Series MicroFC-60035) for bench demos
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2. **TIA**: AD8015 transimpedance amplifier (240 MHz bandwidth, 10 kOhm gain)
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3. **Comparator**: ADCMP607 (3.5 GHz bandwidth, LVPECL output) converts analog pulse to digital timestamp
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3. **Comparator**: ADCMP607 (800 ps propagation delay, CML output) converts analog pulse to digital timestamp
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4. **LLR computation**: RP2040 MCU counts photon arrivals per slot, computes Poisson-model LLRs, writes to Caravel via SPI/UART
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5. **HV bias**: Isolated DC-DC for detector bias (20-70V depending on detector)
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5. **HV bias**: Isolated DC-DC boost converter for SiPM bias (~25-30V)
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**Bill of Materials (Part B additional):**
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@@ -199,10 +200,10 @@ A reference design for the optical receiver frontend, sharing the same PCB as Pa
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| Transimpedance amplifier | AD8015ARZ | 1 | $8 |
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| Fast comparator | ADCMP607BCPZ | 1 | $6 |
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| Companion MCU | RP2040 | 1 | $1 |
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| HV bias module | EMCO Q02-5 | 1 | $15 |
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| SiPM bias supply (30V boost) | LT3482 + passives | 1 | $8 |
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| SMA connector (ext. clock) | SMA-J-P-H-ST-EM1 | 1 | $1 |
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| Passives + connectors | -- | ~20 | $5 |
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| **Part B additional total** | | | **~$66** |
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| **Part B additional total** | | | **~$59** |
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### Full Bench Demo System
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@@ -226,8 +227,10 @@ The Part B SiPM frontend is designed for low-cost bench demos. For operational d
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| Detector | Type | Wavelength | Key Advantage | Typical Use |
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|----------|------|------------|---------------|-------------|
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| BAE Systems GMAPD | Geiger-mode APD array | 1064 / 1550 nm | High sensitivity, proven in NASA/DARPA programs | Deep-space optical, LIDAR |
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| ATI DAPD | Discrete amplification PD | 1550 nm | Photon-number-resolving (PNR) | Quantum optics, high-fidelity optical comm |
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| GMAPD array (MIT Lincoln Lab / BAE) | Geiger-mode APD array | 1064 / 1550 nm | High sensitivity, proven in NASA/DARPA programs | Deep-space optical, LIDAR |
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| Amplification Technologies DAPD | Discrete amplification photon detector | 1550 nm | Photon-number-resolving (PNR) | Quantum optics, high-fidelity optical comm |
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**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.
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**Why photon-number resolution matters for this decoder:**
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@@ -237,7 +240,7 @@ The SiPM and GMAPD in Geiger mode produce binary outputs (click / no-click). The
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LLR_binary = log(P(click | bit=1) / P(click | bit=0))
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```
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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:
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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:
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```
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LLR_PNR(k) = (lambda_s) - k * ln((lambda_s + lambda_b) / lambda_b)
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@@ -256,11 +259,11 @@ The electrical interface is identical to Part B: the detector's analog output fe
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| Item | Est. Cost | Status |
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|------|-----------|--------|
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| chipIgnite shuttle | Contest-covered | GDSII submitted |
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| Part A breakout board (assembled qty 5) | $30-50 | KiCad design complete, fab-ready on silicon return |
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| Part B optical frontend (additional) | ~$66 | Schematic complete, components specified (DNP) |
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| Part A breakout board (assembled qty 5) | $25-40 | KiCad design complete, fab-ready on silicon return |
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| Part B optical frontend (additional) | ~$59 | Schematic complete, components specified (DNP) |
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| Full demo system (TX + RX + optics) | $150-250 | Documented, post-silicon integration |
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| Advanced frontend (GMAPD or DAPD) | $5K-15K | Integration path documented, no ASIC changes needed |
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| **Minimum viable demo** | **$30-50** | **Buildable immediately on silicon return** |
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| **Minimum viable demo** | **$25-40** | **Buildable immediately on silicon return** |
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## Verification Status
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@@ -378,7 +381,7 @@ GDSII layout viewable in KLayout. All DRC checks clean (Magic and KLayout). LVS
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**Phase 2: Silicon Bring-Up (Oct/Nov 2026, on silicon return)**
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- Part A breakout board ordered from JLCPCB (~$2/board, 5-unit MOQ)
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- Components ordered from Digi-Key (~$11 BOM per board)
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- Components ordered from Digi-Key/LCSC (~$8 BOM per board)
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- Board assembly (hand-solder or JLCPCB SMT assembly)
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- First silicon bring-up: VERSION register read over UART, firmware demo execution
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- Measure real-silicon decode latency and power, compare to simulation predictions
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