Minimising this Circuit. Inputs Needed

Hi all,

This is my very first post and I am so glad that I found this wonderful community. Currently I am developing some wireless sensors that makes use of the circuitry attached below. This is an ECG sensor which I adopted from an experiment in Hardvard University. However, since in developing something really small, space is of concern. I am trying to reduce the circuitry below and would love to accept suggestions or solutions on how I can do that.

One of the solution I had in mind was to remove the voltage divider (1.5V) which was used as a voltage rail so the ECG signal would not exceed 1.5V. Please help. Thanks

Secondly, from the diagram circled A,B and C, is there a way that I can calculate these values accurately? I cant seem to recall how to calculate the gains of circles marked A and B. Thanks again.


**broken link removed**

Look into changing the opamps to something that will still work in the application but you can purchase in smaller packages. That will give you most of your size reduction - much more so than passive components.

C1 has unity gain. A1 & B1 are integrators so they are more complicated.

Remember that OpAmps have a very high gain. So the negative feedback makes the voltage at the negative input virtually equal to the voltage at the positive input.

So calculate the voltage at the positive input and then calculate what the output voltage of the Op Amp has to be to make the voltage at the negative input equal.

There was a post about 1 or 2 weeks ago about an integrator, so I suggest you do a search for it. I replied to it, so search for ljcox and "integrator.

Circuit A1 is an integrator, which removes small DC bias.
Circuit B1 is an amplifier/buffer. It has a low frequency gain of about 30, but it's also a low-pass filter.
Circuit C1 generates a Vcc/2 reference, so that the op-amps can operate with a single supply. You can eliminate C1 by taking a center-tap from your (I presume 3V) battery.
OPA2336EA is mis-labeled. You're apparently using OPA4336EA (quad). But you should be able to switch to a dual if you eliminate C1.
None of these components dissipate any noticeable power; I assume you're using, at the largest, 0402 SMD.
If this circuit is more than 1.5 cm^2 (without wires) then keep working on it.

Guys, thank you so much for the inputs. Really appreciate it so much. Currently im trying to reduce the size to somewhat 1cm X 1cm but it is almost impossible to do..

Let me try work something out. In the meantime keep those suggestions coming.