Chapter3 DigitizerBasics
NI5102 User Manual 3-4 ni.com
Vertical Sensitivity
Verticalsensitivity describes the smallest input voltage change the d igitizer
can capture. This limitation is because one distinct digital voltage
encompassesa rangeo f analog voltages. Therefore, it is possible that a
minutechange in voltage at the input is not noticeable at the output of
the ADC. This parameter depends on the input range, gain of the input
amplifier,and AD Cresolution. It is specified in volts per least significant
bit(V/LSB). F igure 3-4 shows the transfer function of a 3-bit ADC with a
vertical range of 5 V having a vertical sensitivity of 5/8 V/LSB.
Figure3-4. Transfer Function of a 3-Bit ADC
ADC Resolution
ADC resolution limitst he accuracy of a measurement. The higher the
resolution (numberof bits), the m ore accuratethe measurement. An 8-bit
ADC divides the vertical range of the input amplifier into 256 discrete
levels.With a vertical range of 10 V, the 8-bit ADC cannot resolve volta ge
differencessmaller than 39m V.In comparison, a 12-bit ADC with
4,096 discrete levels can resolve voltage differences as small as 2.4 mV.
Record Length
Record length refers to the amount of memory dedicated to storing
digitizedsamples for postprocessing or display. In a digitizer, record length
limits the maximum duration of a single-shot acquisition. For example,
witha 1,000-sample buffer and a sample rate of 20 MHz, the duration of
acquisition is 50 µs (the number of points multiplied by the acquisition
time/point or 1,000 ×50 ns). With a 100,000-sample buffer and a sample
Range 0-5 V
Voltage Fluctuations
in This Region Will
Be Unnoticed
000
001
010
011
100
101
110
05V
111