Rainbow Electronics ADC08351 - Manual (Page 14)

Applications Information
(All schematic pin numbers refer to the TSSOP.) (Continued)
ACCURATELY EVALUATING THE ADC
If a signal that is spectrally impure is presented to the ADC,
the output from the ADC cannot be pure. Nearly all signal
generators in use today produce signals that are not spec-
trally pure enough to adequately evaluate present-day
ADCs. This is especially true at higher frequencies and at
high resolutions.
To ensure that the signal you are presenting to the ADC
being evaluated is spectrally pure, use a bandpass filter
between the signal generator and the ADC input. One such
possible filter is the elliptic filter shown in Figure 8.
In addition to being used to eliminate undesired frequencies
from a desired signal, this filter can be used to filter a square
wave, reducing 3rd and higher harmonics to negligible lev-
els. When evaluating dynamic performance of an ADC, repeat-
ability of measurements could be a problem unless coherent
sampling is used.
and ADC08351 evaluation system is available that can sim-
plify evaluation of thsi product.
10089529
FIGURE 7. Inverting Circuit with Bias Adjust
10089531
FIGURE 8. This elliptic filter has a cutoff frequency of about 11MHz and is suitable for input frequencies of 5MHz to
10MHz. It should be driven by a generator of 75 Ω source impedance and teminated with 75Ω. This termination may
be provided by the ADC evaluation circuit.
ADC08351
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