adc161s626cimmx National Semiconductor Corporation, adc161s626cimmx Datasheet - Page 15

• Manufacturer Part Number: adc161s626cimmx
• Description: 16-bit, 50 To 250 Ksps, Differential Input, Micropower Adc
• Manufacturer: National Semiconductor Corporation

2.5 Noise
The noise floor of the ADC161S626 is very low as shown in
Figure 13 and Figure 14. These figures were created by driv-
ing the ADC input with a low-noise voltage source set near
0V. For Figure 13, the input was adjusted in order to obtain
the code 0x0000h. For Figure 14, the input was increased by
1/2 LSB in order to obtain the transition point between code
0x0000h and 0x0001h. In both instances, 2
ples were collected and plotted in a histogram format.
Ideally the noise histogram at code center would show a sin-
gle output code while the noise histogram at code transition
would show two output codes. Any codes outside of the ideal
output are a result of the internal noise of the ADC161S626
and the input source. Since the ADC161S626 has very low
internal noise, only two codes outside of the center code are
exhibited in the histogram of Figure 13. Similar results are
shown in Figure 14.
FIGURE 12. Analog Input CMRR vs. Frequency
FIGURE 13. Noise Histogram at Code Center
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2.6 Input Settling
When the ADC161S626 enters acquisition (t
end of the conversion window, the internal sampling capacitor
(C
and a series resistor (R
ical values for C
respectively. If there is not a large external capacitor (C
at the analog input of the ADC, a voltage spike will be ob-
served at the input pins. This is a result of C
C
direction of the voltage spike depend on the difference be-
tween the voltage of C
C
spike will occur. If the opposite is true, a negative voltage
spike will occur. It is not critical for the performance of the
ADC161S626 to filter out the voltage spike. Rather, ensure
that the transient of the spike settles out within t
ommended solutions, see Section 4.0 in the Application In-
formation.
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FIGURE 14. Noise Histogram at Code Transition
being at different voltage potentials. The magnitude and
is greater than the voltage at C
) is connected to the ADC input via an internal switch
FIGURE 15. ADC Input Capacitors
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and R
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), as shown in Figure 15. Typ-
and C
are 20 pF and 200 ohms
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. If the voltage at
, a positive voltage
ACQ
) mode at the
ACQ
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and
)