
2.7V to 3.6V and 4.5V to 5.5V, Low-Power,
4-/12-Channel, 2-Wire Serial, 12-Bit ADCs
20
______________________________________________________________________________________
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
ADC’s full-scale range, calculate the ENOB as follows:
ENOB = (SINAD - 1.76)/6.02
Total Harmonic Distortion
Total harmonic distortion (THD) is the ratio of the RMS
sum of the input signal’s first five harmonics to the fun-
damental itself. This is expressed as:
where V1 is the fundamental amplitude, and V2 through
V5 are the amplitudes of 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 distor-
tion component.
THD
VVV
V
log
=×
++
+
20
2
3
2
4
2
5
2
1
SINAD dB
SignalRMS
NoiseRMS THDRMS
(
)
log
=×
+
20
*RC NETWORK IS OPTIONAL
**AIN11/REF (MAX1238/MAX1239)
*RS
ANALOG
INPUTS
μC
SDA
SCL
GND
RC NETWORK*
VDD
SDA
SCL
2k
Ω
AIN0
AIN1
AIN3**/REF
3.3V or 5V
5V
RP
CREF
RP
5V
MAX1236
MAX1237
MAX1238
MAX1239
0.1
μF
0.1
μF
Typical Operating Circuit
SDA
SCL
AIN3/REF
1
2
8
7
VDD
GND
AIN1
AIN2
AIN0
MAX
TOP VIEW
3
4
6
5
MAX1236
MAX1237
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
AIN0
AIN8
AIN9
AIN10
AIN11/REF
VDD
GND
SDA
SCL
MAX1238
MAX1239
QSOP
AIN1
AIN2
AIN5
AIN3
AIN4
AIN6
AIN7
Pin Configurations
MAX1236–MAX1239