Rainbow-electronics MAX1422 Manual do Utilizador descarregar pdf (Página 13)

Aperture Delay

Aperture delay (t

) 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

-176

602

MAX1422

12-Bit, 20Msps, +3.3V, Low-Power ADC with

Internal Reference

______________________________________________________________________________________ 13

INPUT

300Ω

-5V

+5V

0.1µF

22pF

1nF0.22µF

44pF*

ISO

50Ω

ISO

50Ω

-5V

600Ω

300Ω

INP

INN

LOWPASS FILTER

CML

600Ω

+5V

-5V

0.1µF

300Ω

600Ω

300Ω

0.1µF

+5V

0.1µF

300Ω

MAX4108

MAX1422

MAX4108

LOWPASS FILTER

*TWO C

(22pF) CAPS MAY BE REPLACED BY

ONE 44pF CAP, TO IMPROVE PERFORMANCE.

Figure 7. Typical Application Circuit for Single-Ended to Differential Conversion

1 2 ... 8 9 10 11 12 13 14 15

Internal Reference 1

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