MAX1219 Datasheet, PDF (19/21 Pages) Maxim Integrated Products – 1.8V, Dual, 12-Bit, 210Msps ADC for Broadband Applications

1.8V, Dual, 12-Bit, 210Msps ADC for
Broadband Applications
Signal-to-Noise Ratio (SNR)
For a waveform perfectly reconstructed from digital
samples, the theoretical maximum SNR is the ratio of
the full-scale analog input (RMS value) to the RMS
quantization error (residual error). The ideal, theoretical
minimum analog-to-digital noise is caused by quantiza-
tion error only and results directly from the ADC’s reso-
lution (N bits):
SNR_dB[max] = 6.02dB x N + 1.76dB
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. RMS noise includes all spec-
tral components to the Nyquist frequency excluding the
fundamental, the first six harmonics (HD2–HD7), and
the DC offset.
Signal-to-Noise Plus Distortion (SINAD)
SINAD is computed by taking the ratio of the RMS sig-
nal to all spectral components excluding the fundamen-
tal and the DC offset. In the case of the MAX1219,
SINAD is computed from a curve fit.
Spurious-Free Dynamic Range (SFDR)
SFDR is the ratio of the RMS amplitude of the funda-
mental (maximum signal component) to the RMS value
of the next-largest noise or harmonic distortion compo-
nent, excluding DC offset. SFDR is usually measured in
dBc with respect to the fundamental (carrier) frequency
amplitude or in dBFS with respect to the ADC’s full-
scale range.
Intermodulation Distortion (IMD)
IMD is the ratio of the RMS sum of the intermodulation
products to the RMS sum of the two fundamental input
tones. This is expressed as:

IMD
=
20
×
log



V^2IM1
+
V^2IM2
+ ...+
V^2IMn


V₁₂ + V₂₂


The fundamental input tone amplitudes (V₁ and V₂) are at
-7dBFS. The intermodulation products are the amplitudes
of the output spectrum at the following frequencies:
• 2nd-order intermodulation products (IM2): f_IN1 + f_IN2,
f_IN2 - f_IN1
• 3rd-order intermodulation products (IM3): 2f_IN1 - f_IN2,
2f_IN2 - f_IN1, 2f_IN1 + f_IN2, 2f_IN2 + f_IN1
• 4th-order intermodulation products (IM4): 3f_IN1 - f_IN2,
3f_IN2 - f_IN1, 3f_IN1 + f_IN2, 3f_IN2 + f_IN1
• 5th-order intermodulation products (IM5): 3f_IN1 - 2f_IN2,
3f_IN2 - 2f_IN1, 3f_IN1 + 2f_IN2, 3f_IN2 + 2f_IN1
Full-Power Bandwidth
A large -1dBFS analog input signal is applied to an
ADC, and the input frequency is swept up to the point
where the amplitude of the digitized conversion result
has decreased by 3dB. The -3dB point is defined as
the full-power input bandwidth frequency of the ADC.
Offset Error
Ideally, the midscale MAX1219 transition occurs at 0.5
LSB above midscale. The offset error is the amount of
deviation between the measured transition point and
the ideal transition point.
Gain Error
Ideally, the positive full-scale MAX1219 transition
occurs at 1.5 LSB below positive full scale, and the
negative full-scale transition occurs at 0.5 LSB above
negative full scale. The gain error is the difference of
the measured transition points minus the difference of
the ideal transition points.
Effective Number of Bits (ENOB)
ENOB specifies the dynamic performance of an ADC at
a specific input frequency and sampling rate. An ideal
ADC’s error consists of quantization noise only. ENOB for
a full-scale sinusoidal input waveform is computed from:
ENOB
=


SINAD −1.76
6.02 
Total Harmonic Distortion (THD)
THD is the ratio of the RMS sum of the first six harmon-
ics of the input signal to the fundamental itself. This is
expressed as:
THD
=

20 × log 
(V₂₂
+ V₃₂
+ V₄₂
+ V₅₂
+ V₆₂
+ V₇₂
)



V₁

where V₁ is the fundamental amplitude, and V₂ through
V₇ are the amplitudes of the 2nd- through 7th-order
harmonics (HD2–HD7).
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