Multichannel Systems MEA1060-Up-BC Manual - Manual (Page 27)

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5 Operating the MEA Amplifier
5.1 Signal Amplification and Filters
The MEA amplifier with blanking circuit is a 60-channel preamplifier with a broad bandwidth.
Filter specifications and gain are defined by the following filter amplifier.
Different filter settings are used for different applications to enhance the signal-to-noise ratio.
The pass band of the filter amplifier should be chosen according to the signal type. It is generally
useful to set the upper limit of the amplifier near the highest expected signal frequency, but also
at a safe distance to make sure that the full gain is used for signal amplification.
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 provides custom amplifiers with a bandwidth of your choice, from 0.1 Hz
to 10 kHz. Please note that it is often useful to acquire the data with a broadband amplifier and
use the digital filter of the free MC_Rack program to change the pass band and filter the raw
data. 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 you will have a lower signal to noise ratio.
The standard gain of a MEA amplifier is 1200 (1100 in case of a MEA amplifier with blanking
circuit), which is fine for most applications, but MCS can also provide amplifiers with a gain of
your choice (from 100 to 5000) as well. For large signals (for example, from whole-heart
preparations), you need a lower gain to prevent a saturation of the amplifier. Please note that
the gain is a fixed hardware property; and that you cannot change the gain of the amplifier by
software controls. For more information on the technical specifications of your amplifier,
please see the separate data sheet that is delivered with each amplifier.
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 , 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 first illustration shows the broad frequency band of the MEA1060-BC amplifier alone
(without Filter Amplifier); the following illustration shows a typical frequency band of the
MEA amplifier with standard gain and bandwidth (in blue). Output signal amplitudes were
divided by the input signal amplitude and the resulting gain was plotted versus the input signal
frequency on a logarithmic scale. A straight line at approximately 70 % of the specified gain
intersects the plotted curve at the lower and upper limit of the pass band. The low-pass filter
property of the combined MEA1060 amplifier and MC_Card (in black) is only slightly different.