dBFS to dBm Calculator

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This tool converts deciBel Full Scale (dBFS) to deciBel milliwatt (dBm).

Enter:

  • dBFS value in dB
  • Peak-to-peak voltage supported by the analog to digital converter
  • Input impedance

The calculator gives the highest spur level in dBm.

Background

Spur Free Dynamic Range (SFDR) is defined as the ratio of the root-mean-square (RMS) value of the peak signal amplitude to the RMS value of the amplitude of the peak spurious. When running an ADC evaluation board, you can observe these experimentally by computing an FFT on the collected time domain samples.

Most Analog-to-digital converter data sheets specify a peak-to-peak voltage.

SFDR and V p-p

If however, an RMS voltage is specified, then use this calculator to convert from V RMS to V peak-to-peak.

Example Calculation

For an 87 dBFS specification with a 2 Volt peak-to-peak input sinusoid and 50 ohm input impedance, the max spur level works out to -77 dBm.