Rainbow Electronics MAX1422 - Manual (Page 13)

Aperture Delay
Aperture delay (t AD ) is the time defined between the
falling edge of the sampling clock and the instant when
an actual sample is taken (Figure 10).
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
quantization error (residual error). The ideal, theoretical,
minimum analog-to-digital noise is caused by quantiza-
tion error only and results directly from the ADCs reso-
lution (N-Bits):
SNR (MAX) = (6.02 ✕ 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 four
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
ADCs error consists of quantization noise only. ENOB is
computed from:
ENOB
SINADdB dB
DdB
=
- 1 76
6 02
.
.
MAX1422
12-Bit, 20Msps, +3.3V, Low-Power ADC with
Internal Reference
______________________________________________________________________________________ 13
INPUT
300 Ω
-5V
+5V
0.1 µF
0.1 µF
0.1 µF
C IN *
22pF
C
IN
*
22pF
1nF 0.22 µF
44pF*
R ISO
50 Ω
R ISO
50 Ω
-5V
600 Ω
300 Ω
300 Ω
INP
INN
LOWPASS FILTER
CML
600 Ω
+5V
-5V
0.1 µF
300 Ω
300 Ω
600 Ω
300 Ω
0.1 µF
0.1 µF
0.1 µF
+5V
0.1 µF
300 Ω
MAX4108
MAX1422
MAX4108
MAX4108
LOWPASS FILTER
*TWO C
IN
(22pF) CAPS MAY BE REPLACED BY
ONE 44pF CAP, TO IMPROVE PERFORMANCE.
Figure 7. Typical Application Circuit for Single-Ended to Differential Conversion