Multichannel Systems STG1000 Manual - Manual (Page 67)

Analog Output Signals
61
Fig. 6 Rise time with programmed 5 V and 500 μA pulses, 100 k
Ω load resistance.
With a higher load resistance, the current pulse (cyan) shows a different kinetic behavior: There is
no overshoot, and the rise time increases significantly (about 20 μs).
11.6 Amplitude-Dependant Time Lag
For most standard applications, you can assume that the STG output is identical (in normal
tolerances of electronic components) to the stimulus protocol in the WYSIWYG editor of the
MC_Stimulus program. However, there are some special situations where you should confirm the
output with an oscilloscope. The deviation from the programmed pulse protocol is due to the
intrinsic properties of the electronic components and may vary slightly between different STG
units. As there is no true linear relationship between, for example, the amplitude dependant time
lag and the amplitude size, the STG's behavior cannot be precisely predicted, and therefore it is
not possible to show a corrected output in the MC_Stimulus display. The only possibility is to
measure the output with an oscilloscope before starting the experiment.
In the following, you will find some general rules that might help you to decide whether your
planned pulse protocol is subject to these limitations. It might be necessary to check and adapt
your pulse protocol according to these findings.
The actual output as shown in the figures below was documented by a standard oscilloscope. The
same pulse protocol and the same channel number of the STG outputs were used for measuring
the voltage and the current output. The devices were set up according to the recommendations
under "Voltage Mode" and "Current Mode".
For very small pulse amplitudes (< 200 mV or < 100 μA), which are generally not used in
biological applications, the time lag between the digital Sync Out output (as a reference point)
and the analog output signals increases with a decreasing amplitude, that is, the lower the
amplitude, the higher the time lag. You should check the actual pulse amplitude and
duration if you need short pulses with a high accuracy. It might be necessary to program longer
pulses to make sure that (a) the output amplitude matches the setpoint voltage and (b) the
duration is long enough for your application. This might be especially important if you apply
biphasic current pulses to discharge the electrode with the inverted phase. In the following, a few
general examples and recommendations are described.
Time lag of positive phase