National Instruments NI 5102 用户手册
Chapter 3
Digitizer Basics
3-4
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Vertical Sensitivity
Vertical sensitivity describes the smallest input voltage change the digitizer
can capture. This limitation is because one distinct digital voltage
encompasses a range of analog voltages. Therefore, it is possible that a
minute change 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 ADC resolution. It is specified in volts per least significant
bit (V/LSB). Figure 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.
can capture. This limitation is because one distinct digital voltage
encompasses a range of analog voltages. Therefore, it is possible that a
minute change 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 ADC resolution. It is specified in volts per least significant
bit (V/LSB). Figure 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.
Figure 3-4. Transfer Function of a 3-Bit ADC
ADC Resolution
ADC resolution limits the accuracy of a measurement. The higher the
resolution (number of bits), the more accurate the 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 voltage
differences smaller than 39 mV. In comparison, a 12-bit ADC with
4,096 discrete levels can resolve voltage differences as small as 2.4 mV.
resolution (number of bits), the more accurate the 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 voltage
differences smaller than 39 mV. 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
digitized samples for postprocessing or display. In a digitizer, record length
limits the maximum duration of a single-shot acquisition. For example,
with a 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
digitized samples for postprocessing or display. In a digitizer, record length
limits the maximum duration of a single-shot acquisition. For example,
with a 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
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
0
5 V
1 1 1