Rainbow Electronics MAX1068 - Manual (Page 27)

MAX1067/MAX1068
Multichannel, 14-Bit, 200ksps Analog-to-Digital
Converters
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Definitions
Integral Nonlinearity
Integral nonlinearity (INL) is the deviation of the values
on an actual transfer function from a straight line. This
straight line can be either a best-straight-line fit or a line
drawn between the end points of the transfer function,
once offset and gain errors have been nullified. The
static linearity parameters for the MAX1067/MAX1068
are measured using the end-point method.
Differential Nonlinearity
Differential nonlinearity (DNL) is the difference between
an actual step-width and the ideal value of ±1 LSB. A
DNL error specification of ±1 LSB guarantees no miss-
ing codes and a monotonic transfer function.
Aperture Definitions
Aperture jitter (t AJ ) is the sample-to-sample variation in
the time between samples. Aperture delay (t
AD
) is the
time between the falling edge of the sampling clock
and the instant when the actual sample is taken.
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
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 ENOB as follows:
ENOB = (SINAD - 1.76) / 6.02
Figure 24 shows the ENOB as a function of the MAX1067/
MAX1068s’ input frequency.
DSP
EXTERNAL
CLOCK
SCLK
DSPR
DSPX
DIN
DOUT
SCLK
TFS
RFS
DT
DR
FL1 CS
MAX1068
Figure 23. DSP Interface Connection
0.1 10 100
FREQUENCY (kHz)
EFFECTIVE BITS
1
14
16
0
2
4
6
8
12
10
f SAMPLE = 200ksps
EFFECTIVE NUMBER OF BITS (ENOB)
Figure 24. Effective Bits vs. Frequency