Chapter 3 Digitizer Basics
NI 5102 User Manual 3-6 ni.com
Figure 3-5. Dynamic Range of an 8-Bit ADC with Three Different Gain Settings
• Source impedance—Many digitizers and most digital storage
oscilloscopes (DSOs) have a 1 MΩ input resistance in the passband
with an X1 probe and a 10 MΩ input resistance with an X10 probe.
If the source impedance is large, the signal will be attenuated at
the amplifier input and the measurement will be inaccurate. If the
source impedance is unknown but suspected to be high, change
the attenuation ratio on your probe and acquire data. If the X10
measurement results in amplitude gain, your measurement may be
inaccurate. To correct this, try reducing the source impedance by
+127 LSB
+38.4 LSB
–38.4 LSB
0 LSB
–128 LSB
+127 LSB
+7 LSB
–8 LSB
0 LSB
–128 LSB
+127 LSB
+153 LSB
–154 LSB
0 LSB
–128 LSB
Acquired Signal
a. Gain = 1, Input Range ±5 V, Number of LSBs = 15
b. Gain = 5, Input Range ±1 V, Number of LSBs = 77
c. Gain = 20, Input Range ±250 mV, Number of LSBs = 307.2
