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Deal with the design challenge of signal acquisition in ECG equipment

the interference signal of ECG includes 50/60hz interference from power supply, motion artifacts caused by patient activities, radio frequency interference caused by electrosurgical equipment, defibrillation pulse, pacemaker pulse and other monitoring equipment. How to deal with the challenges in the process of signal acquisition? This article will show you the solution skills

signal acquisition challenge

the emergence of large DC offset and a variety of interference signals will lead to challenges in the measurement of ECG signals. We can design different fixtures according to different samples and experimental methods. The voltage of typical electrode can reach up to 300mV. Interference signals include 50/60hz interference from the power supply, motion artifacts caused by patient activities, radio frequency interference caused by electrosurgical equipment, defibrillation pulses, pacemaker pulses and other monitoring equipment

the accuracy required in ECG will vary with the change of terminal equipment:

standard monitoring equipment requires a frequency between 0.05 ~ 30Hz

the tempering color of the diagnostic device does not change after heating; The equipment requires a frequency between 0.05 ~ 1000Hz

some 50hz/60hz common mode interference can be offset with the help of a high input impedance instrument amplifier (INA) that can eliminate the common noise of AC lines at two input terminals. In order to further eliminate the line power supply noise, the signal is reversed through the right leg by virtue of the amplifier and driven back to the patient. With only a small amount of micro current or even less, significant CMR improvements can be achieved and kept within the limits of UL544. In addition, 50/60hz digital notch filter will be used to further reduce interference

analog front-end options

optimizing power consumption and PCB area of analog front-end are very critical for portable ECG. After technical improvements, a variety of front-end options are currently available:

1 Use low resolution ADC (all filters required)

2 Using high-resolution WDS ⑶ series, the accuracy is 1% ADC (less filters are required)

3 use Σ-Δ ADC (no filter, amplifier except ina, DC offset)

4 Use sequential and synchronous sampling methods

when using low resolution (16 bit) ADC, the signal needs to be significantly increased (the increase is usually 100 ~ 200 times) to achieve the necessary resolution. Use high resolution (24 bit) Σ-Δ In ADC, the signal needs 4 ~ 5 times of moderate gain. Therefore, the second gain stage and circuit required to eliminate the DC offset can be removed. This will achieve an overall reduction in area and cost. Σ-Δ The method will also retain the entire frequency content of the signal and provide sufficient flexibility for data post-processing

with the help of the sequential method, a single channel that creates ECG leads can be multiplexed to an ADC. In this way, the best thing between adjacent channels is the offset of biodegradable plastics. With the help of synchronous sampling method, dedicated ADC can be used for each channel, so there is no offset between channels mentioned above


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