Multichannel Systems STG4002 Manual - Manual (Page 71)

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11
Analog Output Signals
11.1 Output Modes
The stimulus generator operates in voltage and current mode. Choose voltage or current mode
in the main window of MC_Stimulus II. Please make sure that you use the appropriate stimulation
mode for your experiment. The difference between current and voltage controlled stimulation
is described in the following.
In voltage mode, the voltage level is held constant and the current output depends on the
electrode resistance. The higher the electrode resistance, the lower is the output current.
In current mode, the stimulus generator guarantees a stable current output independent of
the electrode resistance, where the voltage is defined by Ohm's law. The higher the electrode
resistance, the higher is the output voltage. Therefore, the kinetic properties of the stimulus
output is affected by the load resistance, which is usually the electrode resistance. If the
resistance is too high, the output current is limited by the compliance voltage, that is,
too high resistances will result in a clipping of the output signal.
Please consider the time and voltage / current resolution of the stimulus generator.
The minimum pulse has an amplitude of 1 mV in voltage mode or 200 nA in current mode
supported by MC_Stimulus II; the firmware / DLL supports a 14 bit resolution, which means
200 nA for an output current range of 0.8 mA, and a time length of 20 μs. Please note that
if you work near these limits, that is, if you use very small amplitudes or very short pulses,
the output waveform may not exactly match the programmed waveform.
Resolution Limits
Ground
All stimulation channels of the STG are optically isolated from each other. Each channel has an
independent ground (GND), which is usually connected to the ground of the experimental setup,
for example, the amplifier, so that all devices refer to the same ground. Please make sure that you
always use the appropriate ground for the channel in use.