The electrocardiogram
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The electrocardiogram. Op-amps, instrumentation amps, filters. This is your data. V ( arb ). Time (sec). EKG. The EKG is a powerful diagnostic tool. Regularly used by cardiologists. . Disclaimers. We are not real doctors. Neither are you. Do not try to interpret your EKG. . Safety.

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The electrocardiogram

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The electrocardiogram

Op-amps, instrumentation amps, filters


This is your data

V (arb)

Time (sec)


EKG

The EKG is a powerful diagnostic tool. Regularly used by cardiologists.


Disclaimers

  • We are not real doctors. Neither are you. Do not try to interpret your EKG.


Safety


Safety

  • We will review this in lab, but basically

    • 100 K resistors between you and breadboard.

    • Unplug your laptop while collecting data.


Privacy

  • Your EKG could be considered private medical information under Federal HIPAA laws.

  • If using this data makes you at all uncomfortable – then use one of the instructors as your subject.


The circuit

AD623 – Instrumentation amplifier


The Op-Amp


Dynamic model of an op-amp


The op-amp follower


Dynamic model of the follower


Simplification for op-amp circuit analysis

  • If the op-amp is wired with negative feedback, and -

  • Changes are “slow” (less than ~100 kHz), then –

    • Assume no current flow through into the inputs.

    • The two input voltages are equal.


What does this circuit do?


What does this circuit do?


What does this circuit do?


The instrumentation amplifier

Wikipedia


AD623

Data sheet


Let’s look at the filters now…

Vout


Impedance (Z)General form of Ohm’s Law V = I Z

Example: capacitor


RC circuit (via impedances)

Voltage divider

Vout


Do you remember how to plot Vout/Vin ?

w = logspace(0,4,100);

j = sqrt(-1);

R = 10e3;

C = 1e-6;

Z1 = R;

Z2 = 1./(j*w*C);

loglog(w,abs(Z2./(Z1+Z2)));


Resistors in series and parallel

Impedances in series:

Impedances in parallel:

Can you derive these relationships?


What about two filters in series?

Vout

Vin


The circuit


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