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Appendix B Digitizer Basics
©
National Instruments Corporation B-3 NI 5911 User Manual
Figure B-3. 1 MHz Sine Wave Sample
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 LSB. Figure B-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 B-4. Transfer Function of a 3-Bit ADC
1 µ
= Sample Rate 2 MS/s
= Sample Rate 20 MS/s
Range 0-5 V
Voltage Fluctuations
in This Region Will
Be Unnoticed
000
001
010
011
100
101
110
05 V
111
CBIHWum.book Page 3 Thursday, October 29, 1998 1:56 PM