Multichannel Systems ME-System Manual - Manual (Page 17)

Welcome to (USB-) ME-Systems
17
2.6 Signal Amplification and Filters
FA and PGA amplifiers combine a band pass filter and the signal amplification in one instrument.
Different filter settings are used to enhance the signal-to-noise ratio. The pass band of the filter
amplifier depends on the signal type. It is generally useful to filter the data with a cutoff at the
highest signal frequency.
For slow signals like field potentials, a bandwidth of 1 to 300 Hz is appropriate. If you like to
record fast signals like spikes, a pass band of 300 Hz to 3 kHz is suitable. Cardiac signals have
fast and slow components; therefore, you usually need a wider bandwidth of 1 Hz to 3 kHz.
Multi Channel Systems MCS GmbH provides custom amplifiers with a bandwidth of your choice,
from 0.1 Hz to 10 kHz. Please note that it is often wise to acquire the data with a broadband
amplifier and use the digital filter of the MC_Rack program to adjust the pass band. This way,
you are much more flexible in designing your experiments. As a further advantage, you can see
the original (not filtered) data as well. This is especially important because all filters are known
to distort signals. On the other hand, you may need a higher sampling rate to avoid aliasing,
and the signal-to-noise ratio is lower. See also the chapter Data Acquisition for more information.
Multi Channel Systems also provides amplifiers with a gain of your choice (from 100 to 5000).
For large signals (for example, from heart preparations), you need a lower gain to prevent
a saturation of the amplifier. Please note that the gain of FAs is a fixed hardware property;
and that you cannot change the gain of the amplifier by software controls. The gain of
PGAs can be flexibly adjusted for each channel from 10 to 5000.
Please note that the ratio of the output signal to the input signal, that is, the gain, is not
a fixed parameter for the complete bandwidth. The gain that was specified for the amplifier,
for example, 1200, is not fully reached at the borders of the amplifier's pass band. The general
rule is, that at the lower and upper limit of the frequency band, the gain is
2 / 2 , that is
approximately 70 %, of the full gain. Therefore, you should use a bandwidth that is at a safe
distance of the signals of interest. Outside the pass band, the gain decreases with the frequency
and finally approaches zero.
The low-pass filter properties of the MC_Card will affect the bandwidth of the complete system
only slightly.
For information on the gain and filters of the amplifiers, please see the appropriate manual.
For more information on gain and filters in general, please refer to standard literature
or contact your local retailer.