Article Figures & Data
Figures
- Fig. 1.
Basic operation of differential amplifiers. Two inputs come in to an amplifier, and there is one signal output after signal conditioning. If the 2 inputs are of the same polarity and amplitude (upper right), the output signal is zero (common mode rejection of the potentials). If the 2 inputs are of different polarities but the same amplitude (lower right), the output signal is twice the amplitude of the input signals (amplification of different potentials). (From Reference 1, with permission).
- Fig. 2.
Low-frequency filtering. A: A slow oscillatory frequency in the electrocardiogram signal, which may be consistent with respiratory artifact or sweat artifact. B: A 1 Hz low-frequency filter is applied and most of the signal's slow-frequency component is eliminated.
- Fig. 3.
Time constant. The fall time constant refers to the time required for the current from a square wave voltage to decay to 65% of its peak amplitude. Time constant = resistance × capacitance). The low-frequency-filter setting α is 1/time constant. The shorter the time constant the higher the low-frequency-filter setting. The longer the time constant the lower the low-frequency-filter setting.
- Fig. 4.
High-frequency filtering. A: A high-frequency signal that is particularly prominent during inspiration represents snoring artifact. B: A 15 Hz high-frequency filter is applied and the signal's high-frequency component is eliminated.
- Fig. 5.
Notch filtering for 60-Hz artifact. A: A 60-Hz artifact in the submental electromyogram is particularly notable in the first third of the signal. Ideally the technologist should try to replace the sensor to see if the artifact resolves. B: The notch filter appears to significantly attenuate the 60-Hz artifact.
- Fig. 6.
Aliasing. A signal frequency is misrepresented as a slower-frequency waveform. This is typically due to under-sampling. Progressively lower-frequency sampling results in a loss of fidelity of the original waveform.
- Fig. 7.
Balancing concerns in the development of the American Academy of Sleep Medicine Manual for the Scoring of Sleep and Associated Events.
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