How do ADCs affect RF receiver performance?
An ideal N-bit ADC sampling a full-scale sine has quantization-limited SNR = 6.02N + 1.76 dB over the Nyquist band. Real converters are described by SINAD and ENOB = (SINAD − 1.76)/6.02, SFDR, and noise spectral density (dBFS/Hz). Processing gain from filtering to a narrower bandwidth adds 10·log10(fs/(2B)).[1][2]
What is undersampling?
Sampling a band-limited signal in a higher Nyquist zone (above fs/2) aliases it to baseband intentionally, letting the ADC act as a mixer. The ADC’s analog input bandwidth and clock jitter must support the RF frequency; jitter-limited SNR is −20·log10(2πfinσt).[3]
How is ADC noise referred to the antenna?
An ADC can be given an equivalent noise figure: NFADC = PFS(dBm) − SNR − 10·log10(fs/2) + 174 (dB). Front-end gain must lift the antenna noise above this floor without overloading the ADC on blockers — the core analog-digital gain trade-off.[2]
What filtering does an ADC need?
An anti-aliasing filter attenuates signals that would alias into the band of interest. Its requirements fall as sample rate rises; high-speed RF-sampling ADCs often include digital down-converters and decimation filters.
Frequently asked questions
What is ENOB?
Effective number of bits computed from measured SINAD.
Is SFDR the same as SNR?
No; SFDR is carrier-to-largest-spur, SNR includes total noise.
Why does jitter matter more at high frequency?
The voltage error from timing uncertainty is proportional to signal slew rate.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “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.
- “The Data Conversion Handbook”. W. Kester (ed.), Analog Devices / Newnes. 2005.
- “MT-008: Converting Oscillator Phase Noise to Time Jitter”. W. Kester, Analog Devices. tutorial.