Rainbow Electronics MAX1182 - Manual (Page 18)

MAX1182
Dual 10-Bit, 65Msps, +3V, Low-Power ADC with
Internal Reference and Parallel Outputs
18 ______________________________________________________________________________________
Signal-to-Noise Ratio (SNR)
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 quantiza-
tion error (residual error). The ideal, theoretical minimum
analog-to-digital noise is caused by quantization error
only and results directly from the ADC’s resolution
(N-Bits):
SNR dB[max] = 6.02 dB x N + 1.76 dB
In reality, there are other noise sources besides quanti-
zation noise e.g. 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 spec-
tral components minus the fundamental, the first five
harmonics, and the DC offset.
Signal-to-Noise Plus Distortion (SINAD)
SINAD is computed by taking the ratio of the RMS sig-
nal to all spectral components minus the fundamental
and the DC offset.
Effective Number of Bits (ENOB)
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
is computed from:
ENOB
SINAD
dB dB
dB
=
− 1 76
6 02
.
.
MAX1182
0.1 µF
1k Ω
1k Ω 100 Ω
100 Ω
C IN
22pF
C IN
22pF
INB+
INB-
COM
INA+
INA-
0.1 µF
R
ISO
50 Ω
R ISO
50 Ω
REFP
REFN
V
IN
MAX4108
0.1 µF
1k Ω
1k Ω 100 Ω
100 Ω
C IN
22pF
C IN
22pF
0.1 µF
R ISO
50 Ω
R ISO
50 Ω
REFP
REFN
V IN
MAX4108
Figure 7: Using an Op Amp for Single-Ended, AC-Coupled Input Drive