TDT RZ2 Manual page 325

System 3
Signal Resolution
Signal resolution is dependent on the sampling rate used. PCM D/A converters allow
users to generate precise pulsed signals, including square waves with durations of
only 1 sample. When using the maximum sampling rate of ~200kHz, the sample
period is 5.12 microseconds. The IZ2/IZ2H has an effective bandwidth of 80 kHz for
continuous (non-pulsed) waveforms.
Designing the Stimulus Signal
The IZ2/IZ2H Stimulator system offers flexible stimulus delivery capable of generating
complex patterns of pulses or arbitrary waveforms.
This allows you to make use of the full range of the stimulation gizmos in the
Synapse library, or create your own user gizmo for custom stimulation patterns.
IZ2 Serial Number > 2000 or any IZ2H
The Signal Injector gizmo provides default values for the non-stimulating channels.
This can be zero voltage (or current), open circuit, or channel shorted to ground.
Use the IZ2 object settings to enable the shunt resistors on all channels and to
toggle voltage or current mode.
Monitoring the Stimulation
PCM A/D converters on the IZ2/IZ2H monitor the actual output voltage and a
chosen bank of eight channels is sent back to the RZ. This information is available
from the output of the IZ2 object. The IZ2 runtime UI allows you to select which
bank of eight channels is updating on the Monitor output (the rest of the channels
of the Monitor output will be latched) by clicking on the column of LEDs.
Note: There is a single pole 16kHz lowpass filter on these inputs. The filter can affect
impedance checking beyond 10 kHz.
Note: The onboard A/D converters provide the feedback clip at +/-20V, which is higher
than any possible output signal in either voltage or current mode.
Important Notes Regarding the Channel Indicator LEDs
In current mode, the IZ2 can stimulate a maximum 300 uA per channel (up to 15
V) and the IZ2H can stimulate up to 3 mA per channel (up to 15 V) through the
electrode and the return path.
Channels connected to ground (Fill Value set to 'IZ2 Ground' in the Injector gizmo)
are switched into voltage mode and set to output 0V, so the monitored voltage will
always be 0V and the LED status lights for grounded channels will remain dim.
Channels that are open circuit (Fill Value set to 'IZ2 Open' in the Injector gizmo)
in current mode will follow the voltage in the tissue. This must occur so that no
current flows across the electrode. The open circuit electrode then acts like a
recording electrode that is following the voltage at the electrode tip. This may cause
the LED for an Open channel to light up. For example, if there is a 15V potential
relative to ground at the tip of an open circuit electrode, there must also be a 15V
potential on the stimulator side of the electrode so that no current is flowing across
that electrode. Therefore, an open channel nearby the stimulating channel may show
a non-zero voltage on the voltage monitor. If this measured voltage is greater than
7-11
IZ2/IZ2H Stimulator