Chapter3 DigitizerBasics
NI5102 User Manual 3-6 ni.com
Figure3-5. DynamicRange of an 8-Bit ADC with Three Different Gain Settings
•Source impedance—Many digitizers and most digital storage
oscilloscopes (DSOs) havea 1 MΩinput resistance in the passb and
with an X1 probe and a 10 MΩinput resistance with an X10 probe.
Ifthe source impedance is large, the signal will be attenuated at
the amplifierinput and the measurement will be inaccurate. If the
sourcei mpedance is unknownbut suspected to be high, change
the attenuation ratio on your probe and acquire data. If the X10
measurementresults in amplitude gain, your measurement may be
inaccurate. Tocorrect 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