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10 Cards in this Set
- Front
- Back
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Define differential amplifier.
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A differential amplifier amplifies only the difference in voltage between the two inputs. It does not amplify equal (common) voltages at the two inputs. The more the inouts vary in voltage the more there is to amplify,
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Define input impedance.
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NOT the impedance beetween the scalp and the electrodes. Input impedance is impedance between components of the differential amplifier. It must be HIGH for optimal functioning of the amplifier. Must be at least 10 megaohms.
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Define common mode rejection (CMRR).
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The ration of the amplification of the signals that is different in the two inputs of an amplifier to the amplification of the signals that are the same in the two inputs. CMRR rejects external interference such as 60Hz and radio frequencies by canceling signals common to both inputs. The CMRR should be at least 80dB or (10,000:1)
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Describe the polarity convention of an EEG instrument.
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INPUTS UP DOWN
rules rules Input 1 Negative Positive Input 2 Positive Negative |
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The rule in the design of the EEG instruments is that if input 1 is positive with respect to Input 2, the deflection of that channel will be ______.
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Down
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The rule in the design of EEG instruments is that if Input 1 is negative with respect to Input 2, the deflection of the channel will be _______.
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Up
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Define gain.
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The ratio of output signal to input signal. Gain has no units of measurements.
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Define sensitivity.
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a measure of how much voltage is required to cause a deflection of a certain distance; in EEG usually uV/mm
Equation S = V/A S= Sensitivity V= Voltage A= Amplitude |
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Define amplifier.
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a combination of electronic components designed to increase voltage.
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Define time constant.
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The time required for the waveform to fall to 37% of the peak deflection. Describes the effect of the low frequency filter on square wave pulses, i..e., calibration square wave pulse.
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