MAX11645 Maxim Integrated Products, MAX11645 Datasheet - Page 19

• Manufacturer Part Number: MAX11645
• Description: 2-Wire Serial 12-Bit ADCs
• Manufacturer: Maxim Integrated Products

Figure 14. Power-Supply Grounding Connection
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). The ideal, theoretical
minimum analog-to-digital noise is caused by quantiza-
tion error only and results directly from the ADC’s reso-
lution (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, which includes all spectral
components minus the fundamental, the first five har-
monics, and the DC offset.
*OPTIONAL
R* = 5Ω
3V OR 5V
V
DD
SNR
MAX[dB]
2.7V to 3.6V and 4.5V to 5.5V, Low-Power,
______________________________________________________________________________________
MAX11644
MAX11645
1-/2-Channel, 2-Wire Serial, 12-Bit ADCs
0.1µF
4.7µF
= 6.02dB x N + 1.76dB
SUPPLIES
Signal-to-Noise Ratio
GND
V
LOGIC
= 3V/5V
3V/5V
CIRCUITRY
DIGITAL
DGND
GND
Signal-to-noise plus distortion (SINAD) is the ratio of the
fundamental input frequency’s RMS amplitude to the
RMS equivalent of all other ADC output signals.
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:
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 V
V
harmonics.
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.
5
are the amplitudes of the 2nd- through 5th-order
SINAD dB
THD
1
is the fundamental amplitude, and V
=
(
20
ENOB = (SINAD - 1.76)/6.02
)
×
Signal-to-Noise Plus Distortion
=
Spurious-Free Dynamic Range
log
20
⎛ ⎛
⎜
⎜
⎝
Total Harmonic Distortion
×
⎛
⎜
⎝
Effective Number of Bits
log
V
2
2
⎡
⎢
⎣
Noise
+
V
3
2
Signal
RMS
V
+
1
V
www.DataSheet4U.com
4
+
2
RMS
THD
+
V
5
2
RMS
2
⎞
⎟
⎠
⎞
⎟
⎟
⎠
through
⎤ ⎤
⎥
⎦
19