ADC08351CIMTC National Semiconductor, ADC08351CIMTC Datasheet - Page 13

• Manufacturer Part Number: ADC08351CIMTC
• Description: 8-Bit/ 42 MSPS/ 40 mW A/D Converter
• Manufacturer: National Semiconductor

Applications Information
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.
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.
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
FIGURE 7. Inverting Circuit with Bias Adjust
be provided by the ADC evaluation circuit.
(Continued)
source impedance and teminated with 75 . This termination may
13
To ensure that the signal you are presenting to the ADC be-
ing evaluated is spectrally pure, use a bandpass filter be-
tween the signal generator and the ADC input. One such
possible filter is the elliptic filter shown in Figure 8.
7.0 COMMON APPLICATION PITFALLS
Driving the inputs (analog or digital) beyond the power
supply rails. For proper operation, all inputs should not go
more than 300 mV beyond the supply rails. That is, more
than 300 mV below the ground pins or 300 mV above the
supply pins. Exceeding these limits on even a transient basis
may cause faulty or erratic operation. It is not uncommon for
high speed digital circuits (e.g., 74F and 74AC devices) to
exhibit undershoot that goes more than a volt below ground
or above the power supply. Since these conditions are of
very short duration with very fast rise and fall times, they can
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