Rainbow Electronics MAX1207 User Manual
Page 27
MAX1207
65Msps, 12-Bit ADC
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27
Gain Error
Ideally, the positive full-scale MAX1207 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.
Aperture Jitter
Figure 14 depicts the aperture jitter (t
AJ
), which is the
sample-to-sample variation in the aperture delay.
Aperture Delay
Aperture delay (t
AD
) is the time defined between the
rising edge of the sampling clock and the instant when
an actual sample is taken (Figure 14).
Overdrive Recovery Time
Overdrive recovery time is the time required for the
ADC to recover from an input transient that exceeds the
full-scale limits. The MAX1207 specifies overdrive
recovery time using an input transient that exceeds the
full-scale limits by ±10%.
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]
= 6.02
dB
× N + 1.76
dB
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 the RMS noise plus distortion. RMS noise plus
distortion includes all spectral components to the
Nyquist frequency, excluding the fundamental and the
DC offset.
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:
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:
where V
1
is the fundamental amplitude, and V
2
through
V
7
are the amplitudes of the 2nd- through 7th-order
harmonics (HD2–HD7).
Single-Tone Spurious-Free
Dynamic Range (SFDR)
SFDR is the ratio expressed in decibels of the RMS
amplitude of the fundamental (maximum signal compo-
nent) to the RMS amplitude of the next-largest spurious
component, excluding DC offset.
Two-Tone Spurious-Free
Dynamic Range (SFDR
TT
)
SFDR
TT
represents the ratio, expressed in decibels,
of the RMS amplitude of either input tone to the RMS
amplitude of the next-largest spurious component in
the spectrum, excluding DC offset. This spurious
component can occur anywhere in the spectrum up
to Nyquist and is usually an intermodulation product
or a harmonic.
THD
V
V
V
V
V
V
V
=
×
+
+
+
+
+
20
2
2
3
2
4
2
5
2
6
2
7
2
1
log
ENOB
SINAD
=
−
1 76
6 02
.
.
t
AD
T/H
TRACK
HOLD
HOLD
CLKN
CLKP
ANALOG
INPUT
SAMPLED
DATA
t
AJ
Figure 14. T/H Aperture Timing