Portable Health Monitoring Device
A wrist-worn continuous vitals monitor with a Type BF applied part, seven-day battery life and BLE upload to a clinician dashboard.
- Client
- Confidential
- Sector
- —
- Year
- 2025
- Duration
- 26 weeks
- Layers
- 8
- Board size
- 32 × 24 mm
- Placements
- 186
- IPC class
- Class 2
Stack-up: 0.8 mm HDI, 1+N+1 microvia, ENIG, via-in-pad filled and capped
The challenge
The analog front end needed a 20 µVpp noise floor to resolve the PPG signal at low perfusion, on a board 32 mm across that also carried a BLE radio, a buck-boost converter and a colour display. The first-pass prototype from a previous supplier measured 140 µVpp and could not hold a reading during movement.
Our approach
The AFE was moved onto its own quiet island with a dedicated low-noise LDO fed from the switcher, and the display and radio were placed on the opposite side of an eight-layer HDI stack-up with a solid ground layer between them. The buck-boost switching frequency was moved to 2.2 MHz and synchronised to the AFE conversion clock so its residual sits outside the measurement band. Firmware gates the radio so no transmission occurs during a conversion window.
The outcome
Measured noise floor came in at 18 µVpp, inside the target. Battery life reached seven days against a five-day requirement. IEC 62304 Class B documentation was produced alongside the firmware, and the device cleared IEC 60601-1-2 immunity testing without modification.
Measured outcome
140 → 18µVpp
AFE noise floor
7days
Battery life
32 × 24mm
Board area
0cycles
Immunity retest
Noise as a system budget
We allocated the 20 µVpp target across contributors before layout: LDO output noise, conversion clock jitter, switching residual and radio coupling each received a share. That made the design decisions arithmetic rather than argument.
Synchronisation instead of suppression
Filtering a switching residual out of a PPG band costs area and settling time. Moving the converter to 2.2 MHz and locking it to the conversion clock puts the residual where it does no harm — a firmware and clocking decision that saved four passive components and a millimetre of height.
Isolation and applied-part classification
The Type BF classification set creepage and clearance requirements at the electrode interface which fixed the connector position and the keep-out geometry before routing began.
From the bench
The AFE island, separated from the radio by a solid reference layer.
Have a board that needs designing?
Send us the constraints — schematic, mechanical envelope, volume, timeline. You will get a considered response from an engineer within one business day, not a brochure.
We reply within one business day, from an engineer.