1. ECG Biopotential Amplifier ASHLEY MULCHRONE ZEXI LIU

2. Basic Requirements o Take a weak electrical signal from the body, and amplify it (gain ≈ 1000) o Must be designed for a particular frequency range in order to obtain optimal signal to noise ratios o Protects the patient from harm – no currents must appear at the input terminals o High input impedance and low output impedance to provide minimal loading and avoid signal distortion

3. Main Components Preamplifier o Provides initial amplification o High input impedance (≥10 M ) o High CMRR to eliminate large offset signals Driver Amplifier o Amplify signal for appropriate recording Isolation Circuitry o Blocks ECG from unwanted 60 Hz frequencies and high input voltages Driven Right Leg Circuit o Provides a reference point instead of ground

4. Preamplifier Design Vo’ G1 = (V2-V1)/(Vin+ - Vin-) = 1 + 2RF/FG G2 = R2/R1 = 1 Vo’/(V2-V1) = G1G2 = G1 Problem: DC offset could be very big (±300mV) compared to AC signal (~1.5mV) of interest. INA326

5. Solution o Make preamp gain small. o Implement high-pass filtering along with signal conditioning. o Boost AC component via a separate gain stage. o Allows independent adjustment of any desired gain value and performs low-pass filtering of high frequency noise.

7. Preamplification gain G1 = 2 *200k/(40k+40k) = 5 Output stage gain G2 = 1M/5k = 200 Overall gain = 5 * 200 = 1000 High pass filter is designed around A4 to remove DC component, Fcutoff = 1 /(2*pi*RC) ~0.05Hz Low pass filter around A3 to remove high frequency noise, Fcutoff = 1 /(2*pi*RC) = 106.1 Hz

8. Question?