Datasheet

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 effective number
of bits as follows:
ENOB = (SINAD - 1.76) / 6.02
Total Harmonic Distortion (THD)
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
V5 are the amplitudes of the 2nd- through 5th-order har-
monics, respectively.
Spurious-Free Dynamic Range
Spurious-free dynamic range (SFDR) is the ratio of RMS
amplitude of the fundamental (maximum signal compo-
nent) to the RMS value of the next-largest distortion
component.
THD 20 log
VVVVV
V
2
2
3
2
4
2
4
2
5
2
1
=×
++++
⎛
⎝
⎜
⎞
⎠
⎟
MAX1280/MAX1281
400ksps/300ksps, Single-Supply, Low-Power, 8-Channel,
Serial 12-Bit ADCs with Internal Reference
22 ______________________________________________________________________________________
SCLK
DIN
DOUT
SSTRB
SEL2START SEL1 SEL0 PD1 PD0
CS
UNI/BIP SGI/DIF
B10 B1
MSB
B0
HIGH IMPEDANCE
HIGH IMPEDANCE
Figure 19. MAX1280/MAX1281-to-TMS320 Serial Interface
V
DD
I/O
SCK (SK)
MOSI (SO)
MISO (SI)
V
SS
SSTRB
DOUT
DIN
SCLK
COM
GND
V
DD2
V
DD1
CH8
4.7µF
0.1µF
CH0
0 TO
+2.5V
ANALOG
INPUTS
MAX1280
MAX1281
CPU
SHDN
CS
+5V OR
+3V
REF
0.01µF
REFADJ
Typical Operating Circuit