Multichannel Systems STG1000 Manual - Manual (Page 73)

Analog Output Signals
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Fig. 12 STG output with programmed 200 mV and 20 μA pulses, duration 100 μs for each phase.
About 10 μs is the standard delay of the voltage output at 200 mV (U, yellow). The delay of the
current output at 20 μA (cyan) is increased due to the small current amplitude. At 100 μA or
higher, the time lag of the current output would be comparable to the standard delay of the
voltage output.
11.7 Capacitive Behavior of Stimulating Electrodes
Regarding the generally used stimulus pulses, stimulating electrodes behave as plate capacitors.
They need some time to discharge themselves after stimulation. As a result, artifacts interfere with
the recording, and electrodes deteriorate over time due to electrolysis. This effect takes place
especially in current mode because the current cannot flow back to the stimulus generator due to
the high output resistance in current mode and thus is kept in the electrode.
To reduce the effect described abovew in current mode, you should use biphasic pulses for
stimulation. The stimulus signal should be immediately followed by an inverse signal of the same
area (product of current and time), which helps to discharge the electrode. The easiest way is to
use the same signal amplitude with an opposite polarity.
Multi Channel Systems recommends to use voltage driven stimulation. In voltage mode, it is not
necessary to use a biphasic stimulation for discharging the electrodes, because the electrode
should be discharged at a voltage of 0, that is, it would be sufficient to apply the negative phase
only.
Warning: When using MEA electrodes of TiN material, stimulation with a higher amplitude is
possible if you apply the negative pulse first . Also, regard the safe charge-injection limit
as described in the MEA User Manual. Otherwise, electrodes can be damaged during stimulation.