🫀 ECG Analog Front-End — PCB Design & Implementation

ENGR-UH 3611: Electronics | NYU Tandon School of Engineering
A full-semester project designing an ECG acquisition system from Cadence simulation to a hand-soldered PCB, culminating in a miniaturized battery-powered board small enough to fit a smartwatch.

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🎯 Project Overview

Design, simulate, and physically implement an ECG (Electrocardiogram) analog front-end capable of acquiring, filtering, and outputting a clean heartbeat signal from body surface electrodes — progressively miniaturizing the design across three phases.

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📋 Signal Chain

Body Electrodes (3-lead: LA, RA, RL)
        ↓
Instrumentation Amplifier — INA121 (Gain: 500 V/V)
        ↓
Driven Right Leg (DRL) Circuit — common-mode noise reduction
        ↓
Active Band-Pass Filter (0.3 Hz – 100 Hz) — isolates ECG band
        ↓
Twin-T Notch Filter (50/60 Hz) — powerline interference removal
        ↓
Clean ECG Output ✓

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🔁 Project Phases

Phase 1 — Simulation (Cadence Virtuoso)

Designed and validated the full ECG signal chain in Cadence Virtuoso before any physical implementation. All simulation files are in pcb_v1/simulation/.

• Instrumentation Amplifier (3 op-amp topology): Gain of 500 V/V via R_gain (R1 = 510kΩ, Rg = 2kΩ). Verified CMRR and robustness against 10% component mismatch.
• Body Model Simulation: Built a Body_Model_ECG cell in Cadence with LA, RA, RL electrode nodes and 50 Hz coupling capacitors to simulate real powerline interference.
• DRL Circuit: Designed and simulated Driven Right Leg feedback. Compared three cases: floating DRL (unstable), DRL to ground (improved), and active DRL feedback (best CMRR).
• Active Band-Pass Filter (0.3 Hz – 100 Hz): Single op-amp topology, mid-band gain ~2, designed with Rf > R3 and R1C1 >> R2C2.
• Twin-T Notch Filter (50 Hz): RC notch with buffer op-amp. Designed using f₀ = 1/(2πRC), R3 = R/2, C1 = 2C. AC analysis confirmed 50 Hz attenuation.

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Phase 2 — Custom PCB v1 (Altium Designer, ≤ 7cm × 7cm)

Transferred the validated simulation circuit to a custom PCB designed in Altium Designer. All components hand-soldered using SMD and through-hole techniques.

Board specs:

• Supply: ±VDD/VSS dual-rail (2× CR2032 batteries)
• Input: 3.5mm audio jack (SJ-3523-SMT-TR) for LA, RA, RL electrode connection
• Op-amps: TLV9041 (U2–U5)
• 6 decoupling capacitors (1nF, 100nF, 10µF per rail) for stable power delivery
• Full signal chain on a single board — Power Stage, Instrumentation Stage, BP Filter, Twin-T Notch, DRL Stage
• 0805 SMD resistors and capacitors

📹 Signal output demo: Watch on Google Drive

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Phase 3 — Watch-Size PCB (Altium Designer, ≤ 4.5cm × 4.5cm)

Redesigned the full ECG front-end to fit a 3.8cm × 3.5cm form factor — small enough for a smartwatch enclosure — powered by a single CR1616 coin cell battery.

Design constraints:

• PCB dimensions: ≤ 4.5cm × 4.5cm (final: 3.8cm × 3.5cm)
• Single CR1616 coin cell — includes VDD/VSS/GND generation circuitry
• 0805 SMD components only — no through-hole
• On-board LED for power status indication
• On/off power switch
• Audio jack (SJ-3523-SMT-TR) for INN, INP, DRL electrode inputs
• Header pins for VDD, VSS, GND, and signal output only
• Custom schematic and PCB component libraries built from scratch in Altium
• Component cost validated against Digikey (USD)

File	Description
WatchSchematic.SchDoc	Full schematic — all circuit stages
PCB1.PcbDoc	PCB layout file
WatchPCB_Project.BomDoc	Bill of Materials
PedroF_plf2030_gerbers/	Gerber files for fabrication

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🛠️ Tech Stack

Tool	Role
Cadence Virtuoso	Schematic design and SPICE simulation (Phase 1)
Altium Designer	PCB schematic, layout, and Gerber generation (Phases 2–3)
Breadboard + Oscilloscope	Physical validation of signal chain
Hand soldering	SMD and through-hole component assembly

Key ICs: INA121 (instrumentation amplifier), TLV9041 (op-amps), SJ-3523-SMT-TR (3.5mm audio jack)

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📂 Repository Structure

ECG-PCB/
├── pcb_v1/
│   ├── schematic/          ← Altium schematic
│   ├── pcb_layout/         ← Altium PCB layout
│   ├── photos/             ← Physical soldered board
│   └── simulation/         ← Cadence simulation reports (Pre-Lab 4 & 5 PDFs)
│       ├── PreLab4_PedroF.pdf    (IA design + Cadence simulation)
│       └── PreLab5_PedroF.pdf    (Body model, DRL, Twin-T Notch)
├── watch_pcb/
│   ├── schematic/          ← WatchSchematic screenshots
│   ├── pcb_layout/         ← PCB layout screenshots
│   ├── gerbers/            ← PedroF_plf2030_gerbers/
│   └── bom/                ← WatchPCB_Project.BomDoc
└── README.md

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📊 Results

📹 ECG signal output (PCB v1): Watch on Google Drive

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👤 Author

Pedro Felix | Electrical Engineering — NYU Tandon School of Engineering
GitHub