MAX1156 Datasheet, PDF (13/15 Pages) Maxim Integrated Products – 14-Bit, 135ksps, Single-Supply ADCs with Bipolar Analog Input Range

14-Bit, 135ksps, Single-Supply ADCs with
Bipolar Analog Input Range
Signal-to-Noise Ratio
For a waveform perfectly reconstructed from digital
samples, signal-to-noise ratio (SNR) is the ratio of the
full-scale analog input (RMS value) to the RMS quanti-
zation error (residual error). The ideal, theoretical mini-
mum analog-to-digital noise is caused by quantization
noise error only and results directly from the ADC’s res-
olution (N bits):
SNR = (6.02 × N + 1.76) dB
where N = 14 bits.
In reality, there are other noise sources besides quanti-
zation noise; thermal noise, reference noise, clock jitter,
etc. SNR is computed by taking the ratio of the RMS
signal to the RMS noise, which includes all spectral
components minus the fundamental, the first five har-
monics, and the DC offset.
Signal-to-Noise Plus Distortion
Signal-to-noise plus distortion (SINAD) is the ratio of the
fundamental input frequency’s RMS amplitude to the
RMS equivalent of all the other ADC output signals.
SINAD(dB)
=
20
×
log



Signal_RMS
(Noise + Distortion)_RMS



Effective Number of Bits
Effective number of bits (ENOB) indicates the global
accuracy of an ADC at a specific input frequency and
sampling rate. An ideal ADC’s error consists of quanti-
zation noise only. With an input range equal to the full-
scale range of the ADC, calculate the effective number
of bits as follows:
ENOB = ^{SINAD −1.76}
6.02
Total Harmonic Distortion
Total harmonic distortion (THD) is the ratio of the RMS
sum of the first five harmonics of the input signal to the
fundamental itself. This is expressed as:

THD
=
20
×
log



V₂₂
+
V₃₂
+
V₄₂
+
V₅₂


V₁


where V₁ is the fundamental amplitude and V₂ through
V₅ are the 2nd- through 5th-order harmonics.
Spurious-Free Dynamic Range
Spurious-free dynamic range (SFDR) is the ratio of the
RMS amplitude of the fundamental (maximum signal
component) to the RMS value of the next largest fre-
quency component.
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