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Understanding ADC Resolution Differences on USB-6008/6009 Input Modes

Updated Aug 7, 2026

Reported In

Hardware

  • USB-6008
  • USB-6009

Issue Details

I noticed that the USB-6008/6009 User Guide lists different ADC resolutions for differential and single-ended measurements. I want to understand why the single-ended resolution is one bit lower than the differential resolution as shown in the following table:
 
ModelADC Resolution
NI USB-600812 bits differential
11 bits single-ended
NI USB-600914 bits differential
13 bits single-ended

 

I want to understand why the single-ended resolution is one bit lower than the differential resolution.

Solution

The USB-6008/6009 uses the Analog-to-Digital Converter (ADC) differently depending on the configured input mode.
  • Use differential mode when measuring the voltage difference between two input signals.
  • Note that differential measurements use the full ADC range, allowing both positive and negative values to be represented directly.
  • Understand that one ADC bit functions as the sign bit when operating in differential mode.

 

For single-ended measurements:
  • Measure signals relative to the common ground reference.
  • Recognize that the ADC uses only the positive portion of its range.
  • Expect the effective resolution to decrease by one bit because the sign bit is not required.

 

Although the sign bit is not used for single-ended measurements, negative voltages can still be measured.
  • Use the internal resistor network that scales the input range from -10 V to +10 V into a 0 V to +10 V range before reaching the ADC.
  • Note that only half of the ADC range is available to represent the full analog input range.
  • Expect the effective measurement resolution to be reduced by one bit compared to differential mode.

Additional Information

The resolution difference is a result of how the ADC range is allocated in each measurement mode rather than a limitation of the hardware itself.
 
For newer NI USB data acquisition devices such as the USB-6001, USB-6002, and USB-6003, the analog input architecture differs from that of the USB-6008 and USB-6009. As a result, the ADC resolution specification remains the same regardless of whether the analog input channel is configured for differential or single-ended measurements.

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