AD9640SLASHPCB datasheet(16/41 Pages) AD

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AD9640

Preliminary Technical Data

Rev. PrD | Page 16 of 41

TERMINOLOGY

Crosstalk

Coupling onto one channel being driven by a (−0.5 dBFS) signal

when the adjacent interfering channel is driven by a full-scale

signal. Measurement includes all spurs resulting from both

direct coupling and mixing components.

IF Sampling (Undersampling)

Due to the effects of aliasing, an ADC is not necessarily limited

to Nyquist sampling. Frequencies above Nyquist are aliased and

appear in the first Nyquist zone (dc to Sample Rate/2). Care

must be taken to limit the bandwidth of the sampled signal so

that it does not overlap Nyquist zones and alias onto itself. IF

sampling performance is limited by the bandwidth of the input

SHA (sample-and-hold amplifier) and clock jitter. (Jitter adds

more noise at higher input frequencies.)

Nyquist Sampling (Oversampling)

Oversampling occurs when the frequency components of the

analog input signal are below the Nyquist frequency (Fclock/2),

and requires that the analog input frequency be sampled at least

two samples per cycle.

Out-of-Range Recovery Time

Out-of-range recovery time is the time it takes for the analog-

to-digital converter (ADC) to reacquire the analog input after a

transient from 10% above positive full scale to 10% above

negative full scale, or from 10% below negative full scale to 10%

below positive full scale.

Signal-to-Noise Ratio (SNR)

The ratio of the rms value of the measured input signal to the

rms sum of all other spectral components within the pro-

grammed DDC filter bandwidth, excluding the first six

harmonics and dc. The value for SNR is expressed in

decibels (dB).

Two-Tone IMD Rejection

The ratio of the rms value of either input tone to the rms value

of the worst third-order intermodulation product; reported

in dBc.ADC Equivalent Circuits

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