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EEG Digital Concepts

practice for EEG registry

QuestionAnswer
Describe an A/D Converter. A device that converts the continuous analog EEG signal to numbers or digits. This conversion is done by sampling the epoch of EEG at pre-selected intervals and recording the polarity and amplitude of the wave at each of those points.
What should the input impedance be for a digital EEG instrument? Greater than 10 mega-ohms.
Define aliasing. When the ADC samples the analog signal at a rate less than twice its fastest frequency, and the analog signal is then misinterpreted as a slower frequency waveform.
Define the Nyquist frequency. The Nyquist frequency is also known as the critical sampling rate. It must be at least twice the fastest frequency, if sampling is slower, aliasing can occur.
Describe the effects of digital filtering on a waveform. Digital filtering causes a phase shift where the waveform appears to be advanced or delayed in time. Excessive low frequency filtering (LFF) causes a shift to the left; excessive high frequency filtering (HFF) causes a shift to the right.
What should the sampling rate be for a digital EEG instrument? A minimum of 200 Hz, Preferably 250-450Hz
Define Sampling rate. The number of digital points per second used to represent the analog signal. Number of points/analysis time
What should the common mode rejection ratio (CMRR) be for a digital EEG Instrument? The common mode rejection ration (CMRR) should be at least 80 dB.
What should the analog to digital conversion specifications be for a digital EEG instrument. Greater or equal to 12 bit ADC. The recording should be able to resolve activity down to 0.5 mV and as high as several millivolt without clipping.
Created by: moeegtech