What is dynamic range and SFDR?

From RF Design Wiki · By the RF Design Wiki editorial team · Published October 21, 2026 · Last reviewed October 21, 2026 · How we research

Dynamic range is the ratio between the largest and smallest signals a system can handle. The spurious-free dynamic range (SFDR) is the range over which two-tone IM3 products stay below the noise floor: SFDR = ⅔·(IIP3 − N_in) in dB, where N_in = −174 + NF + 10·log10(B) is the input-referred noise floor.^[1]

How is SFDR derived?

IM3 referred to the input is P_IM3,in = 3P_in − 2·IIP3. Setting it equal to N_in gives the maximum input P_in,max = (2·IIP3 + N_in)/3, and SFDR = P_in,max − N_in = ⅔(IIP3 − N_in). Some definitions subtract the required SNR from the upper limit.^[1]

What other dynamic range definitions exist?

Compression dynamic range: from noise floor (or sensitivity) to P1dB.
Blocking dynamic range: largest off-channel signal causing 1 dB desensitization.
ADC SFDR: ratio of full-scale carrier to largest spur, in dBc or dBFS.^[2]
Spectrum analyzer dynamic range: optimized by input attenuation that balances DANL and internally generated distortion.^[3]

How can dynamic range be improved?

Lower NF and narrower bandwidth lower the floor; higher IIP3 (more bias current, feedback, better devices) raises the top. Pre-selection filtering keeps strong out-of-band signals from reaching nonlinear stages. Automatic gain control trades instantaneous for total dynamic range.

Frequently asked questions

Why is SFDR two-thirds of the range to IIP3?

Because IM3 rises 3 dB for every 1 dB of input, it reaches the noise floor two-thirds of the way to IIP3.

Is SFDR bandwidth dependent?

Yes; wider bandwidth raises the noise floor and reduces SFDR.

What limits SDR dynamic range?

Often the ADC's SFDR and the analog front-end linearity.

References

Online sources accessed October 21, 2026; printed works cited by edition. See all sources.

“RF Microelectronics, 2nd ed.”. B. Razavi, Prentice Hall. 2012.
“MT-003: Understand SINAD, ENOB, SNR, THD, THD + N, and SFDR so You Don't Get Lost in the Noise Floor”. W. Kester, Analog Devices. tutorial.
“Spectrum Analysis Basics (Application Note 150)”. Keysight Technologies. application note.

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