max5864 Maxim Integrated Products, Inc., max5864 Datasheet - Page 23

• Manufacturer Part Number: max5864
• Description: Max5864 Ultra-low-power, High-dynamic-performance, 22msps Analog Front End
• Manufacturer: Maxim Integrated Products, Inc.

ADC and DAC Static Parameter Definitions
Integral nonlinearity 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 lin-
earity parameters for the device are measured using
the end-point method (DAC Figure 12a).
Differential nonlinearity is the difference between an
actual step width and the ideal value of 1 LSB. A DNL
error specification of less than 1 LSB guarantees no
missing codes (ADC) and a monotonic transfer function
(ADC and DAC) (DAC Figure 12b).
Ideally, the midscale 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.
Offset error
ideal and actual offset point. The offset point is the out-
put value when the digital input is midscale. This error
affects all codes by the same amount and usually can
be compensated by trimming.
Ideally, the ADC full-scale transition occurs at 1.5 LSB
below full scale. The gain error is the amount of devia-
tion between the measured transition point and the
ideal transition point with the offset error removed.
Figure 13. T/H Aperture Timing
Dynamic Parameter Definitions
DATA (T/H)
SAMPLED
ANALOG
INPUT
(Figure
CLK
T/H
t
AD
TRACK
______________________________________________________________________________________
Performance, 22Msps Analog Front End
12a) is the difference between the
Differential Nonlinearity (DNL)
Integral Nonlinearity (INL)
t
HOLD
AJ
ADC Offset Error
DAC Offset Error
Ultra-Low-Power, High Dynamic-
ADC Gain Error
TRACK
Figure 13
sample-to-sample variation in the aperture delay.
Aperture delay (t
rising edge of the sampling clock and the instant when
an actual sample is taken
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) and results directly
from the ADC’s resolution (N bits):
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 five harmonics, and the DC offset.
SINAD is computed by taking the ratio of the RMS sig-
nal to the RMS noise. RMS noise includes all spectral
components to the Nyquist frequency excluding the
fundamental and the DC offset.
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:
THD is typically the ratio of the RMS sum of the first five
harmonics of the input signal to the fundamental itself.
This is expressed as:
where V
the amplitudes of the 2nd- through 6th-order harmonics.
THD
SNR(max) = 6.02dB x N + 1.76dB (in dB)
1
ADC Dynamic Parameter Definitions
is the fundamental amplitude and V
depicts the aperture jitter (t
=
ENOB = (SINAD - 1. 76) / 6.02
Signal-to-Noise Plus Distortion (SINAD)
20log
AD
) is the time defined between the




Effective Number of Bits (ENOB)
Total Harmonic Distortion (THD)
(V + V + V + V + V )
2
2
(Figure
Signal-to-Noise Ratio (SNR)
3
2
13).
V
1
4
2
AJ
Aperture Delay
Aperture Jitter
5
2
), which is the
6
2
2
–V




6
are
23