Chapter2 HardwareOverview
©NationalInstruments Corporation 2-5 NI5911 User Manual
Oscilloscope Mode
The ADC converts at a constant rate of 100 MS/s, but you can choose to
store only a fraction of these samples into memory at a lower rate. This
allowsyou tostore waveforms using fewer data points and decreases the
burden of storing, analyzing, and displaying the waveforms. If you need
fastersampling rates, you can use Random Interleaved Sampling (RIS) to
effectively increasethe sampling rate to 1 GS/s for repetitive waveforms.
In oscilloscope mode, all signals up to 100 MHz are passed to the ADC.
Youneed to ensure that your signal is band-limited to prevent aliasing.
Aliasing and other sampling terms are described more thoroughly in
Appendix B, Digitizer Basics.
Sampling Methods—Real Time and RIS
Thereare two sampling methods available in oscilloscope mode, Real Time
and RIS. Using real times ampling,you can acquire data at ar ate of
100 MS/nwherenis a number from1 to 4.3 mill ion. RIS sampling can be
used on repetitive signals to effectively extend the sampling rate above
100 MS/s. In RIS mode, you can sample at rates of 100 MS/s * n, where n
is a number from 2 to 10. The available sampling rates, resolutions, and
bandwidth for flexible resolution mode are shown in Table 2-2.
Flexible Resolution Mode
Table 2-2 shows the relationship between the available sampling rates and
the corresponding bandwidth for flexible resolution mode.
Table2-2. Available Sampling Rates and Corresponding Bandwidth
inFlexible Resolution Mode
Sampling Rate Resolution Bandwidth
12.5MS/s 12bits 4MHz
5MS/s 14bits 2MHz
2.5 MS/s 16 bits 800kHz
1MS/s 18bits 400kHz
500 kS/s 18 bits 200 kHz
200 kS/s 19 bits 80kHz
100 kS/s 19 bits 40kHz
50kS/s 20bits 20kHz