STK RevM20 sensor front end

Simultaneous electrochemical sensing on a compact four-layer flex PCB

Prototype · 3 current channels + pH · 4-layer FPC · 41.8 × 42.5 mm

Key design decisions

  • Acquisition and coupling. Continuous TIAs and simultaneous ADC sampling preserve channel timing. Shared RE/CE saves connections, with electrical and chemical crosstalk left for measurement.
  • Precision and sourcing. The ADG704 substitution was checked for pin/control compatibility. Leakage, on-resistance, resistor tolerance and reference errors drive the per-range calibration plan.
  • Layout and assembly. GND/power continuity, high-impedance inputs and USB routing were reviewed. Double-sided FPC assembly requires fixture, reflow and USB mechanical-support review.

STK RevM20: continuous TIAs and pH buffer, simultaneous ADC, DAC setpoints and ESP32-S3 USB acquisition

Verification and next step

CAD evidence: 0 DRC/ERC violations and 0 unconnected items under the configured checks; BOM/placement matching for 196 fitted parts. Audit scope and exclusions.

Next: factory review → USB-only bring-up → dummy-cell accuracy, noise and crosstalk tests. Reset/startup and selected-channel EIS still need physical validation. No measured accuracy is claimed.

Requirements · Error budget · Validation plan · 한국어

RevM20 / FW18 · Design baseline: 15 October 2026 · Earlier AD5941 toolkit