Multichannel Systems MEA2100-System Manual - Manual (Page 38)

MEA2100-System Manual
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4.5 Bandwidth and Gain Specification
The MEA2100 amplifier with blanking circuit is a 120-channel headstage with a hardware defined
bandwidth. Default settings for the hardware filter will be 1 Hz to 3 kHz. However, a different
bandwidth can be achieved by an additional software program, called “MEA2100 Configuration”,
no hardware modification is necessary. The firmware defined bandwidth marks the upper and
lower limit of the frequency range, filtering within this range can be done with software filters
in MC_Rack.
Note: To change the filter settings, you can use the add on software “MEA2100 Configuration”.
Please see the manual for the “MEA2100 Configuration” software in the Appendix.
Depending of the hardware revision the MEA2100-System, it has a fixed hardware gain factor
of 5, the gain factor is 2 in older hardware revisions.
The ADCs (Analog Digital Converter) of the MEA2100 system have a resolution of 24 bit,
the MC_Rack software can record and display data with a resolution of 16 bit. To handle the
complete 24 bit range, the input voltage range selection in the MC_Rack software can select
a window of 16 bit out of these 24 bits, resulting in the following signal ranges:
+/- 812 μV; +/- 1727 μV, +/- 3545 μV; +/- 7090 μV;
+/- 14 mV; +/- 28 mV, +/- 57 mV; +/- 114 mV; +/- 227 mV
A smaller input range results in a better resolution in bits/μV, signals larger than the selected
range will be clipped. In summary, the procedure has exactly the same functionality as a software
selectable gain, even though, strictly speaking, it is not.
DC Offset Correction
The internal baseline restore routine is used to eliminate DC offsets of the electrode channels
and set all baseline values to zero. This has to be a slow process. If the routine corrected too fast,
slow signals would be eliminated as well.
All electrodes on an array have different DC offsets at the beginning of an experiment. The
DC offsets are amplified by the headstage, and the amplified output signal of the preamplifier
is likely to exceed the input range of the filter amplifier. In order to eliminate this DC offset,
a so-called baseline restorer is integrated in the headstage. For signals in the usual measurement
range, the baseline restore routine acts like a high pass filter with a very low cut-off frequency
of roughly 0.01 Hz.
Due to the low cut-off frequency, the baseline restorer takes some time to stabilize after
switching on the amplifier or after replacing the MEA. One to two minutes are quite normal.
During this time, the filter amplifier input will be overloaded and you will see only a straight
line with very low noise. This is considered a normal behavior and should not trouble you.
Please wait until the baseline restore routine has been completed. After about one minute, the
baseline restorer of the headstage has corrected the DC offset, and the output signals are now
in the operating range of the filter amplifier. You should see now a noise level of about 20 μV.