Biomedical Instrumentation

System Constraints and Models

Browser port of the Webster / Northrop four-panel figure. Drag the sliders — the same equations as biomedical_signal_models_visualizations.py update live.

1. Skin-electrode source loading

\(V_{measured}=V_{bio}\,Z_{in}/(Z_{in}+Z_{skin})\), \(Z_{skin}=100\,\mathrm{k}\Omega\)

Amplifier \(Z_{in}\): 10 MΩ

2. Linear vs nonlinear transduction

Thermistor \(R(T)=R_0 e^{\beta(1/T-1/T_0)}\) vs strain-gauge \(V \propto P\)

3. InAmp 60 Hz common-mode rejection

\(A_d=1000\), \(V_{cm}=100\,\mathrm{mV}\) at 60 Hz, \(\mathrm{CMRR}_{dB}=20\log_{10}|A_d/A_{cm}|\)

CMRR: 80 dB

4. Johnson (thermal) noise floor

\(V_{n,rms}=\sqrt{4 k_B T R \Delta f}\)

T: 300 K

Δf: 500 Hz

References: Webster, Medical Instrumentation: Application and Design; Northrop, Analysis and Application of Analog Electronic Circuits in Biomedical Engineering.