5- Amplifier Flashcards
Define what’s the voltage
The voltage is the difference in electrical potentials.
Site two requirement for measurement of electrical signals.
Noise and interference should be as low as possible and the measurement should influence the signal as low a possible.
Site the Amplitude and frequencies of ECG and the place for recording.
Electrocardiogram - Thorax - >1000 microVolts - 0,01-300Hz
Site the Amplitude and frequencies of EEG and the place for recording.
Electroencephalogram - Skull - 50 microvolts - 0.06 to 100 Hz
Site the Amplitude and frequencies of EVP and the place for recording.
Brain evoked potentials - skull - 20 micro volts - 1 to 300 Hz
Site the Amplitude and frequencies of ERG and the place for recording.
Electroretino gram - Cornea - >100 microvolt - 0 to 20 Hz
Site the Amplitude and frequencies of EMG and the place for recording.
Electromyogram - Muscle - >1000 microvolts - 10 to 5000 Hz
What’s the nyquist theorem ?
It says you should sample twice as fast as the higher signal component of the signal is, in other words you should oversample.
What is the aim of “OVERSAMPLING” ?
Allows the analysis of details in the signal
Site the basic component of a recording system.
1- Body as the source 2-Electrodes for recording 3- DC decoupling (All commo, signal due to electrode polarisation or skin contact create a voltage drop). 4- Pre Amplifier 5- Filter 6- Decoupling for patient safety (patient should not be directelly linked to voltage) 7- ADC 8- Saving and processing
Site and define the different amplifier requirements
1-High input impedance & Low input capacitance (done is most cases by selecting an amplifiers with metal oxide semi conductor field effect transistor or MOS FET)
2-High common mode rejection ratio (done with high quality components, symmetric design and differential amplifier)
3-A low input bias current (input transistors, capacitive decoupling)
4-Low Interferences (low noise circuitry, high signal to noise ratio and a shielded setup).
Site the four types of analogue filters and define their role.
Low pass (allows only low frequency) High pass (for decoupling of DC signal) Band pass (increases the signal to noise ratio, you can select a frequency range) and Notch filter (reduces the main hum=bourdonnement, you select a specific frequency so it doesn't work if wanted signal is in this frequency range)
Describe the principle of a differential amplifier
amplifies the difference between two input voltages but suppresses any voltage common to the two inputs. It has two input terminals, a ground and a output terminal. .
What’s the difference between an open loop gai and a differential amplification ?
OLG without wiring, diff ampl with wiring.
Define the use, the unitity and the calculus of Common mode rejection ratio.
Number that gives you an idea of how good your AMP is to amplify a certain Diff signal without amplifying a common mode signal. The idea is to short circuit both input terminal and see how much does that system amplify. The unity is dB and the calculus is : 20xlog(/vid- div /Vg/).
