MAX1332 Datasheet, PDF (23/25 Pages) Maxim Integrated Products – 3Msps/2Msps, 5V/3V, 2-Channel, True-Differential 12-Bit ADCs

3Msps/2Msps, 5V/3V, 2-Channel, True-
Differential 12-Bit ADCs
CNVST
ANALOG
INPUT
t_AD
t_AJ
SAMPLED
DATA (T/H)
T/H ^TRACK
HOLD
TRACK
Figure 21. T/H Aperture Timing
between the measured midscale transition point and
the ideal midscale transition point.
Gain Error
Gain error is a figure of merit that indicates how well the
slope of the actual transfer function matches the slope
of the ideal transfer function. For the MAX1332/
MAX1333, the gain error is the difference of the mea-
sured full-scale and zero-scale transition points minus
the difference of the ideal full-scale and zero-scale
transition points.
For the unipolar input, the full-scale transition point is
from 0xFFE to 0xFFF and the zero-scale transition point
if from 0x000 to 0x001.
For the bipolar input, the full-scale transition point is
from 0x7FE to 0x7FF and the zero-scale transition point
is from 0x800 to 0x801.
Aperture Jitter
Aperture jitter (t_AJ) is the sample-to-sample variation in
the aperture delay.
Aperture Delay
Aperture delay (t_AD) is the time defined between the
falling edge of the CNVST and the instant when an
actual sample is taken (Figure 21).
Signal-to-Noise Ratio (SNR)
SNR is a dynamic figure of merit that indicates the con-
verter’s noise performance.
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] = 6.02_dB x N + 1.76_dB
In reality, there are other noise sources such as thermal
noise, reference noise, and clock jitter that also
degrade SNR.
For the MAX1332/MAX1333, SNR is computed by tak-
ing the ratio of the RMS signal to the RMS noise. RMS
noise includes all spectral components to the Nyquist
frequency excluding the fundamental, the first five har-
monics, and the DC offset.
Signal-to-Noise Plus Distortion (SINAD)
SINAD is a dynamic figure of merit that indicates the
converter’s noise and distortion performance.
SINAD is computed by taking the ratio of the RMS sig-
nal to the RMS noise plus distortion. RMS noise plus
distortion includes all spectral components to the
Nyquist frequency excluding the fundamental and the
DC offset:
SINAD(dB)
=
20
×
⎡
log_⎢
⎣
(NOISE
SIGNAL_RMS
+ DISTORTION)_RMS
⎤
⎥
⎦
Effective Number of Bits (ENOB)
ENOB specifies the global accuracy of an ADC at a spe-
cific 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 a dynamic figure of merit that indicates how much
harmonic distortion the converter adds to the signal.
THD is the ratio of the RMS sum of the first five harmon-
ics of the fundamental signal to the fundamental itself.
This is expressed as:
⎛
THD = 20 × log^⎜
V2²
+
V3²
+
V4²
+
V5²
+
V6²
⎞
⎟
⎝⎜
V1
⎠⎟
where V₁ is the fundamental amplitude, and V₂ through
V₆ are the amplitudes of the 2nd- through 6th-order
harmonics.
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