Model 2601B-PULSE System SourceMeter Instrument Reference Manual Section 4: Sourcing and measuring
2601B-PULSE-901-01A April 2020 4-41
Operation considerations for the ADC
The following paragraphs discuss autozero and NPLC caching with the analog-to-digital converter (on
page 7-1) (ADC).
Autozero
When the pulser is disabled, the ADC of the 2601B-PULSE uses a ratiometric A/D conversion
technique. To ensure reading accuracy, the instrument must periodically obtain fresh measurements
of its internal ground and voltage reference. Separate reference and zero measurements are used for
each aperture.
You can set autozero to occur automatically or turn it off and run it manually.
By default, autozero is set to AUTO, which automatically checks the reference measurements
whenever a signal measurement is made. If the reference measurements are out of date when a
signal measurement is made, the instrument automatically makes two more A/D conversions, one for
the reference and one for the zero, before returning the result. Thus, occasionally, a measurement
takes longer than normal. This extra time can cause problems in sweeps and other test sequences in
which measurement timing is critical.
To avoid the extra time for the reference measurements, you can select OFF. This setting disables
the automatic reference measurements. Note that with automatic reference measurements disabled,
the instrument may gradually drift out of specification. Select the autozero ONCE option to refresh the
reference and zero measurements that are used for the current aperture setting.
To minimize the drift, a reference and zero measurement should be made immediately before critical
test sequences.
When the pulser is enabled, two high-speed digitizing sampling ADCs are used to measure voltage
and current. These ADCs do not use a ratiometric conversion technique, so the autozero settings are
ignored when the pulser is enabled.
Front-panel autozero
To change autozero from the front panel:
1. Press the CONFIG key.
2. Press the MEAS key.
3. Turn the navigation wheel to select AUTO-ZERO, and then press the ENTER key or the
navigation wheel .
4. Turn the navigation wheel to select the mode (OFF, ONCE, or AUTO), and then press the
ENTER key or the navigation wheel .
5. Press the EXIT (LOCAL) key to return to the previous display.
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