Datasheet

MAX1162
16-Bit, +5V, 200ksps ADC with 10µA
Shutdown
16 ______________________________________________________________________________________
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 ADCs res-
olution (N bits):
SNR = (6.02 x 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,
excluding the DC offset.
Effective Number of Bits
Effective number of bits (ENOB) indicate the global
accuracy of an ADC at a specific input frequency and
sampling rate. An ideal ADC error consists of quantiza-
tion noise only. With an input range equal to the full-
scale range of the ADC, calculate the effective number
of bits as follows:
ENOB = (SINAD - 1.76) / 6.02
Figure 13 shows the effective number of bits as a func-
tion of the MAX1162’s input frequency.
Total Harmonic Distortion
Total harmonic distortion (THD) is 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
1
is the fundamental amplitude and V
2
through
V
5
are the 2nd- through 5th-order harmonics.
Spurious-Free Dynamic Range
Spurious-free dynamic range (SFDR) is the ratio of the
RMS amplitude of the fundamental (maximum signal
component) to the RMS value of the next largest fre-
quency component.
Supplies, Layout, Grounding,
and Bypassing
Use PC boards with separate analog and digital
ground planes. Do not use wire-wrap boards. Connect
the two ground planes together at the MAX1162 (pin 3).
Isolate the digital supply from the analog with a low-
value resistor (10Ω) or ferrite bead when the analog
and digital supplies come from the same source
(Figure 14).
THD
VVVV
V
=×
+++
⎡
⎣
⎢
⎢
⎢
⎤
⎦
⎥
⎥
⎥
20
2
2
3
2
4
2
5
2
1
log
SINAD dB
Signal
Noise Distortion
RMS
RMS
( ) log=×
+
()
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
20
INPUT FREQUENCY (kHz)
EFFECTIVE BITS
101
2
4
6
8
10
12
14
16
0
0.1 100
ENOB vs. INPUT FREQUENCY
Figure 13. Effective Number of Bits vs. Input Frequency
SCLK
DOUT
AGND
DGND
AIN
10Ω
REF
AV
DD
DV
DD
DOUT
SCLK
CS
AIN
V
REF
+5V
4.7µF
0.1µF
0.1µF
GND
MAX1162
CS
Figure 14. Powering AV
DD
and DV
DD
from a Single Supply