MAX1333 Maxim Integrated Products, MAX1333 Datasheet - Page 23

• Manufacturer Part Number: MAX1333
• Description: (MAX1332 / MAX1333) True-Differential 12-Bit ADCs
• Manufacturer: Maxim Integrated Products

Figure 21. T/H Aperture Timing
between the measured midscale transition point and
the ideal midscale transition point.
Gain error is a
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 (t
the aperture delay.
Aperture delay (t
falling edge of the CNVST and the instant when an
actual sample is taken (Figure 21).
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-
DATA (T/H)
SAMPLED
ANALOG
CNVST
INPUT
T/H
figure of merit that indicates how well the
AJ
t
AD
AD
) is the sample-to-sample variation in
______________________________________________________________________________________
TRACK
Signal-to-Noise Ratio (SNR)
) is the time defined between the
3Msps/2Msps, 5V/3V, 2-Channel, True-
t
AJ
HOLD
Aperture Delay
Aperture Jitter
TRACK
Gain Error
Differential 12-Bit ADCs
tion error only and results directly from the ADC’s reso-
lution (N bits):
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.
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:
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:
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:
where V
V
harmonics.
6
SINAD dB
are the amplitudes of the 2nd- through 6th-order
Signal-to-Noise Plus Distortion (SINAD)
THD
1
(
is the fundamental amplitude, and V
=
SNR
20
)
Effective Number of Bits (ENOB)
Total Harmonic Distortion (THD)
=
×
dB[max]
20
log
ENOB
×
⎛
⎜
⎜
⎝
log
V
= 6.02
2
⎡
⎢
⎣
=
(
2
NOISE DISTORTION
+
SINAD
V
3
dB
6 02
2
.
SIGNAL
+
+
x N + 1.76
−1 76
V
V
4
1
.
2
+
V
RMS
5
2
dB
+
V
2
)
6
RMS
through
2
⎞
⎟
⎟
⎠
⎤
⎥
⎦
23