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An electrocardiogram (ECG) is a recording of the electrical activity on the body surface generated by the heart. ECG measurement information is collected by skin electrodes placed at designated locations on the body. The ECG signal is characterized by six peaks and valleys labeled with successive letters of the alphabet P, Q, R, S, T, and U
The front end of an ECG must be able to deal with extremely weak signals ranging from0.5 mV to5.0 mV, combined with a dc component of up to ±300 mV—resulting from the electrode-skin contact—plus a common-mode component of up to1.5 V, resulting from the potential between the electrodes and ground. The useful bandwidth of an ECG signal, depending on the application, can range from0.5 Hz to50 Hz—for a monitoring application in intensive care units—up to1 kHz for late-potential measurements (pacemaker detection). A standard clinical ECG application has a bandwidth of0.05 Hz to100 Hz.
ECG signals may be corrupted by various kinds of noise. The main sources of noise are:1- power-line interference:50–60 Hz pickup and harmonics from the power mains2-electrode contact noise: variable contact between the electrode and the skin, causing baseline drift3-motion artifacts: shifts in the baseline caused by changes in the electrode-skin impedance4-muscle contraction: electromyogram-type signals (EMG) are generated and mixed with the ECG signals5-respiration, causing drift in the baseline6-electromagnetic interference from other electronic devices, with the electrode wires serving as antennas, and7-noise coupled from other electronic devices, usually at high frequencies.
for power and control desgin must be take attention for the following
Safe PowerThe isolated power is supplied by a battery, which is recharged in a charging station when not in use. Both supply voltages (±5 V) are generated by capacitive charge pumps, which cannot generate unsafe voltages—even under fault conditions—because they do not require any inductors. These devices also feature a shutdown mode,which allows the MicroConverter to power down the devices when the system is not in use.
In addition to the control circuit and the safe power supply, the series resistors, Rx1, Rx2, and Rx3, provide protection for the patient—in order to comply with AAMI (Association for the Advancement of Medical Instrumentation) standards for safe current levels. These standards require that rms ground currents or fault current from the electronics must be less than50 µA .
