Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

FILTERING AN ECG SIGNAL - before or after the notch?

Status
Not open for further replies.

spottymaldoon

New Member
I have taken Analog Devices' standard application of their AD620 op amp to make the front end of an electrocardiograph (three electrodes are strapped to the subject).

In the attached schematic this is followed by a tunable 60 Hz notch filter with a dual op amp buffer stage and followed by a high pass filter (1000Mfd capacitor) at "B".

A simple op amp amplifier with gain 100 follows and the output is connected to a 10 bit 3 V A/D converter (using PIC24FJ).

I am worried about the placement of the high pass filter at "B" - its purpose is to minimize the grossest low frequency excursions of the signal (e.g when the subject moves) and I could have placed it at "A"

I'd be obliged if somebody would comment on this whole arrangement and whether the big cap would be better placed elsewhere? Please also comment on my switch to single power supply devices for the latter stages.
 

Attachments

  • ECG schematic.jpg
    ECG schematic.jpg
    188 KB · Views: 4,077
You might be interested in the ECG circuit given in the datasheet for the AD8420. Apparently, the problem with the circuit in the AD620 datasheet is that the DC excursions that occur when the patient moves are amplified by the AD620 limiting the gain that the AD620 can be set at, because those DC excursions are amplified and can saturate the AD620. That's not ideal because the inamp is where you want most of the gain due to the high CMRR provided by the inamp. In the AD8420 datasheet circuit, the DC excursions are canceled out in the inamp, by using an integrator to drive the REF pin, and so the gain of the inamp can be set much higher without saturating the output with DC excursions. Then the inamp is followed only with a low pass filter with a 50 Hz corner to attenuate 60 Hz noise and other higher frequency noise.
 
Hi, am working on a project of a heart rate monitor and am planning to use the fingertip method. Jst need suggestions which sensor I can preferably use.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top