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docs: fix BOM errors found in adversarial review

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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:
cah
2026-03-30 22:03:08 -06:00
parent 8898cb7b95
commit 5774b03e60
1 changed files with 39 additions and 36 deletions
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75
README.md
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@@ -10,7 +10,7 @@ A soft-input LDPC decoder ASIC targeting the ChipFoundry chipIgnite shuttle (Sky
### Free-Space Optical Downlinks (CubeSat, UAV-to-Ground) ### 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 ### Underwater Optical Modems
@@ -108,24 +108,25 @@ A minimal breakout board for silicon bring-up and firmware demo, designed for im
``` ```
USB-C USB-C
| |
+-----v------+ +-----v------+ +--------+
| FT232RL | +--------+ | CH340C | | SPI |
| USB-UART |---->| SPI | | USB-UART |---->| Flash |
+-----+------+ | Flash | +-----+------+ | W25Q32 |
| | W25Q32 | | +---+----+
+-----v------+ +---+----+ +-----v------+ |
| AP2112K | | | AP2112K | +----v-----------+
| 3.3V LDO | +----v-----------+ | 3.3V LDO | | |
+-----+------+ | | +-----+------+ | Caravel |
| | Caravel | | | QFN-64 |
+-----v------+ | QFN-64 | +-----v------+ | (LDPC decoder |
| AP2112K | | (LDPC decoder | | AMS1117 | | inside) |
| 1.8V LDO |-->| inside) | | 1.8V 1A |-->| |
+-----+------+ | | +-----+------+ +----+-----------+
| +----+-----------+ | |
+-----v------+ | +-----v-----------+ |
| 25 MHz XTAL|--------+ | SiT8008 25 MHz |--+
+------------+ | CMOS oscillator |
+-------------------+
Reset btn, Power LED, 2x Status LEDs 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 | | 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 | | 3.3V LDO regulator | AP2112K-3.3TRG1 | 1 | $0.35 |
| 1.8V LDO regulator | AP2112K-1.8TRG1 | 1 | $0.35 | | 1.8V LDO regulator (1A) | AMS1117-1.8 | 1 | $0.25 |
| USB-UART bridge | FT232RL | 1 | $4.50 | | USB-UART bridge | CH340C | 1 | $0.50 |
| SPI flash (32 Mbit) | W25Q32JVSSIQ | 1 | $0.65 | | SPI flash (32 Mbit) | W25Q32JVSSIQ | 1 | $0.65 |
| USB-C connector | USB4110-GF-A | 1 | $0.60 | | USB-C connector | USB4110-GF-A | 1 | $0.60 |
| Decoupling caps (100nF) | CL05B104KO5NNNC | 12 | $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 | | Reset button | PTS645SM43SMTR92 | 1 | $0.15 |
| LEDs + resistors | -- | 5 | $0.50 | | LEDs + resistors | -- | 5 | $0.50 |
| PCB fabrication (qty 5) | JLCPCB 2-layer FR4 | 1 | $2.00 | | 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) ### 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--------+ +-------------+ +----------+ +----v--------+ +-------------+ +----------+
| GMAPD/SiPM |---->| TIA |---->| Fast | | GMAPD/SiPM |---->| TIA |---->| Fast |
| Detector | | AD8015 | | Comp. | | Detector | | AD8015 | | Comp. |
| (HV bias) | | 240 MHz BW | | ADCMP607 | | (bias ~30V) | | 240 MHz BW | | ADCMP607 |
+----+---------+ +-------------+ +----+-----+ +----+---------+ +-------------+ +----+-----+
| | | |
+----v--------+ +----v-----+ +----v--------+ +----v-----+
@@ -187,9 +188,9 @@ A reference design for the optical receiver frontend, sharing the same PCB as Pa
**Part B signal chain:** **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 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) 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 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):** **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 | | Transimpedance amplifier | AD8015ARZ | 1 | $8 |
| Fast comparator | ADCMP607BCPZ | 1 | $6 | | Fast comparator | ADCMP607BCPZ | 1 | $6 |
| Companion MCU | RP2040 | 1 | $1 | | 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 | | SMA connector (ext. clock) | SMA-J-P-H-ST-EM1 | 1 | $1 |
| Passives + connectors | -- | ~20 | $5 | | Passives + connectors | -- | ~20 | $5 |
| **Part B additional total** | | | **~$66** | | **Part B additional total** | | | **~$59** |
### Full Bench Demo System ### 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 | | 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 | | GMAPD array (MIT Lincoln Lab / BAE) | 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 | | 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:** **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)) 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) 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 | | Item | Est. Cost | Status |
|------|-----------|--------| |------|-----------|--------|
| chipIgnite shuttle | Contest-covered | GDSII submitted | | chipIgnite shuttle | Contest-covered | GDSII submitted |
| Part A breakout board (assembled qty 5) | $30-50 | KiCad design complete, fab-ready on silicon return | | Part A breakout board (assembled qty 5) | $25-40 | KiCad design complete, fab-ready on silicon return |
| Part B optical frontend (additional) | ~$66 | Schematic complete, components specified (DNP) | | Part B optical frontend (additional) | ~$59 | Schematic complete, components specified (DNP) |
| Full demo system (TX + RX + optics) | $150-250 | Documented, post-silicon integration | | 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 | | 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 ## 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)** **Phase 2: Silicon Bring-Up (Oct/Nov 2026, on silicon return)**
- Part A breakout board ordered from JLCPCB (~$2/board, 5-unit MOQ) - 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) - Board assembly (hand-solder or JLCPCB SMT assembly)
- First silicon bring-up: VERSION register read over UART, firmware demo execution - First silicon bring-up: VERSION register read over UART, firmware demo execution
- Measure real-silicon decode latency and power, compare to simulation predictions - Measure real-silicon decode latency and power, compare to simulation predictions