Multichannel Systems STG1000 Manual - Manual (Page 55)

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11 Analog Output Signals
11.1 Output Modes
The stimulus generator operates in voltage and current mode and has separate voltage and
current outputs for each channel. Regardless of the operation mode selected in MC_Stimulus,
both current and voltage outputs are active. Please make sure that you use the appropriate
output for your experiment. The main difference between the current outputs and the voltage
outputs 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, that 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.
Warning: Do not connect any device between a voltage (U) and a current output (I). This could
damage the stimulus generator.
Please regard the time and voltage/current resolution of the stimulus generator. The minimum
pulse has an amplitude of 2 mV in voltage mode or 1 μA in current mode (supported by
MC_Stimulus II; the firmware/DLL supports a 13 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
match the programmed waveform.
Ground
All up to 8 STG channels are optically isolated from each other. Each channel has an independent
ground output (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.
11.2 Voltage Mode
• If you operate the STG in voltage mode, you will usually use the +U and GND outputs. The output
signal is identical with the programmed signal in the normal ranges of the electronics' accuracy.
See illustration "Voltage mode: Standard Setup".
• It is strongly recommended to short-circuit the +I and I outputs with the provided cables for