MAX1422 Datasheet, PDF (13/15 Pages) Maxim Integrated Products – 12-Bit, 20Msps, 3.3V, Low-Power ADC with Internal Reference

12-Bit, 20Msps, 3.3V, Low-Power ADC with
Internal Reference
300Ω
5V
0.1µF
0.1µF
MAX4108
-5V
0.1µF
LOWPASS FILTER
INP
R_ISO
50Ω
C_IN*
22pF
300Ω
600Ω
5V
INPUT
MAX4108
0.1µF
0.1µF
-5V
0.1µF
600Ω
300Ω
300Ω
300Ω
300Ω
600Ω
5V
0.22µF
44pF*
1nF
MAX1422
CML
0.1µF
MAX4108
-5V
0.1µF
LOWPASS FILTER
INN
R_ISO
50Ω
C_IN*
22pF
300Ω
*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
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 = ^SINAD-1.76
6.02
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