# ECG Circuit Analysis: Calculating Contribution of Eint to Vout

• Engineering
• Ariastity
In summary, the contribution of Eint to the output voltage Vout is not valid, because you cannot neglect the loading effects of the other voltage sources. You must use nodal analysis to solve for Vbody.
Ariastity
What is the contribution of Eint
to the output voltage Vout?

## The Attempt at a Solution

To calculate the contribution of Eint, I removed the other two voltage sources.

Then, I divided them into three potential dividers, giving me:

Vbody= (ZC2/ZC2+ZC1) x Eint;
V1=(Zin1/ZB1+Zin1) x Vbody;
and V2=(Zin2/ZB2+Zin2 )x Vbody

Lastly, Vout= Vbody- V1-V2.

Is this method valid?

You can isolate the contribution of Eint by suppressing the other sources as you've done. That's fine.

The Vbody voltage divider is not isolated. It's loaded by the two other voltage dividers. So you can't rely on the voltage divider equation to produce the true value for Vbody. That mucks up the calculation of V1 and V2 since they both depend on Vbody.

Use nodal analysis for the three nodes (V1, V2, Vbody) to handle the dependencies.

You haven't yet specified what the gain of the amplifier is, so it's not possible to say what Vout will be given V1 and V2.

berkeman

gneill said:
Use nodal analysis for the three nodes (V1, V2, Vbody) to handle the dependencies.

I tried using nodal analysis only to get Vbody without applying voltage divider, and it gives me:
icouple1=(Eint-Vbody)/Zcouple1
and icouple2=Vbody/Zcouple2,
with icouple1=icouple2+ibody.

I don't really know how to go on from there and quantify Vbody in terms of Eint, as further nodes only give me equations that depend on the value of Vbody.

If you have three nodes you need to write three node equations. They will be be interdependent (simultaneous equations) that need to be solved together.

In this case, since it is assumed that the amplifier input impedance is being represented by the external impedances Zin, you could ignore V1 and V2 for now and treat the ZB and Zin pairs as branches of the Vbody node. You'd have to go back and solve for V1 and V2 later. But the important thing is that you can't ignore the loading effects of these branches on the Vbody node when you solve for Vbody. The single-node version of the circuit would look like this:

Note how the two ZB branches parallel the ZC2 impedance. You can write a single node equation to solve for Vbody in this case, taking into account all the branches.,

## What is an ECG circuit?

An ECG (electrocardiogram) circuit is a type of electronic circuit that measures and records the electrical activity of the heart. It is used to diagnose and monitor heart conditions.

## What is Eint and Vout in an ECG circuit?

Eint is the voltage generated by the heart's electrical activity, which is measured by the ECG circuit. Vout is the output voltage of the ECG circuit, which is used to create the visual representation of the heart's electrical activity.

## How is Eint calculated in an ECG circuit?

Eint is calculated by measuring the difference in voltage between two electrodes placed on the skin, which are connected to the ECG circuit. The circuit then amplifies and filters the signal to produce the Eint voltage.

## What is the contribution of Eint to Vout in an ECG circuit?

The contribution of Eint to Vout in an ECG circuit is the relationship between the input voltage (Eint) and the output voltage (Vout). This is determined by the circuit's design and components, and can be calculated using Ohm's law and Kirchhoff's laws.

## Why is calculating the contribution of Eint to Vout important in ECG analysis?

Calculating the contribution of Eint to Vout is important in ECG analysis because it allows us to accurately interpret the heart's electrical activity. By understanding the relationship between the input and output voltages, we can identify abnormalities and diagnose heart conditions.

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