ECG IN-Amp Gain Resistor Question

[twincitian]

Hi.

First time posting. Wish I had found this site months ago, would have come in handy.

As shown in the picture(taken from openECGproject : 3-Lead Wireless ECG document):



The gain resistor for the IN-Amp is actually made up of 3 resistors. The center tap of the two 22K resistors going to the DRL(Driven Right Leg) connection.

According to the document:
"This method was utilized because two separate amplifiers
needed to be interfaced to the right leg common-mode driver". This comment I don't understand.

Anyone know why this was done instead of using just two resistors, each having half the value of Rg and using the center tap for the DRL?

Thanks Much.

 

[crutschow]

The comment says two separate amplifiers need to be interfaced to the right leg common-mode driver. Do you know what those two separate amps are? If you posted the complete circuit, the reason for the three resistor may be more apparent.

But, in general, it would seem that you could use two resistors instead of three.

 

[twincitian]

Hi.

Thanks for the response.

The document is located at:
**broken link removed**
There is no main schematic, only portions of it.

The driver for the right leg is listed but only one amplifier is shown. Not sure where else they meant for the DRL signal to go.

I agree it seems I should be able to use only two resistors. In fact, a number of schematics I found use only two resistors. This schematic recently popped up and I thought it was interesting enough to investigate. I will probably go with the three resistor design because it's easy and cheap but I won't have a good explanation for the customer as to why I did it that way.

Anybody got any ideas?

Thanks