Resolution and Input Range

The resolution of the A/D converter on a digitiser card, or D/A converter of a waveform generator, defines the smallest voltage difference (voltage step) that can in theory be recognized. The table below gives the theoretical step changes for different resolutions within commonly used input range settings. The actual resolution (ENOB or Effective Number Of Bits) depends on further factors in the design of the cards front-end circuity.

Resolution makes a big difference to what can be seen of a signal shape, which is why so much effort goes into the design of the Spectrum cards. Compared to a 8 bit converter the resolution of the 12 bit and 14 bit A/D are 16 and 64 times better respectively, whilst 16 bit it is 256! There is always some trade-off between speed of conversion and resolution, however the latest converters can provide remarkably high resolution up into the GHz sampling range.


    Voltage Step per LSB for given +/- range
Resolution Steps +/- 50 mV +/- 100 mV +/- 200 mV +/- 500 mV +/- 1 V +/ 2 V +/- 5 V +/- 10 V
8 Bit 256 390 uV 780 uV 1.6 mV 3.9 mV 7.8 mV 15.6 mV 39 mV 78 mV
12 Bit 4096 24.4 uV 48.8 uV 0.1 mV 0.24 mV 0.49 mV 1 mV 2.4 mV 4.9 mV
14 Bit 16384 6 uV 12 uV 24 uV 61 uV 122 uV 244 uV 610 uV 1.2 mV
16 Bit 65536 1.5 uV 3 uV 6 uV 15 uV 30 uV 61 uV 152 uV 305 uV



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