ECG (Heart) Signal Acquisition

We get many requests for assistance on the design of ECG (heart signal) monitoring. Please understand that, though we have some familiarity with these designs, we are not authorities on the subject. We have never designed production equipment of this type.

Requirements for ECG signal acquisition can vary widely. Acquisition of a signal to detect heart rate, for example, may be very simple. Input circuitry for diagnostic equipment must be very high performance and is more complex and demanding. There is a whole range of applications between these extremes. We find it very difficult to judge the scale and needs of your project.

There are many tradeoffs that can dramatically affect the design and amplifier selection:

  • Single power supply or dual (±) power supply
  • Supply voltage
  • Current consumption requirements
  • Size or package type restrictions
  • Galvanic isolation requirements
  • Type of electrodes and leads
  • Temperature range
  • Expected usage and noise environment

There is no one “best” amplifier for ECG signal acquisition. The right selection may be any one of perhaps 30 different types depending on the factors listed above (and others that we can’t guess). Very good input stages can be made with general purpose op amps. One general recommendation, however, may save you some time and grief—FET or CMOS amplifiers are generally provide better signals. Their very low input bias current reduces signal artifacts produced by the varying electrode contact resistance when the subject moves.

Single supply circuitry may seem simple and appealing but these designs can be more challenging to implement. Dual (±) power supply designs are generally easier.

Optimization of tricky parts of the circuit (such as right-leg drive) can be difficult for experienced circuit designers working with hands directly on the equipment. Much depends on your electrode and lead configuration and other factors that are difficult to predict or replicate. These issues can be virtually impossible for us to diagnose from afar.

Our assistance is best limited to help with specific circuit problems once a design approach is selected. Questions such as “can you recommend a circuit” leave us bewildered. We can help with amplifier selection if we know something of the influencing factors (the list above). Otherwise, we’re just guessing.

Note to Students—

ECG signal acquisition appears to be a popular class assignment or research project. We understand why. There is much theory to be learned and practical application experience to be gained from this type of project. We don’t want to deprive you of an important learning opportunity or discourage innovation by providing a “canned solution.” Furthermore, a good solution will vary greatly, depending on the goals of the project and factors mentioned above. Good luck.

Resources:

6204.Design Considerations for ECG Systems.pdf   Presentation with general background on ECG signal acquisition

6114.ECG Cardiotachometer.pdf   An ECG Cardiotachometer Design Example

ADS1298 ECG Data Acquisition System Component, product page

INA333 product data sheet. See figures 36 and 37.