Datasheet

Single-Ended Input
1.25
0.0 0.75 1.75 2.5
3.75
V
A
= 5.0V
V
REF
(V)
COMMON-MODE VOLTAGE (V)
2.5
0
5
-1
6
1.25
Differential Input
1.25
0.0 1.0 2.0 3.0 4.0 5.0
3.75
V
A
= 5.0V
V
REF
(V)
COMMON-MODE VOLTAGE (V)
2.5
0
5
-1
6
2.5
ADC161S626
www.ti.com
SNAS468C SEPTEMBER 2008REVISED MARCH 2013
Since the design of the ADC161S626 is optimized for a differential input, the performance degrades slightly when
driven with a single-ended input. Linearity characteristics such as INL and DNL typically degrade by 0.1 LSB and
dynamic characteristics such as SINAD typically degrade by 2 dB. Note that single-ended operation should only
be used if the performance degradation (compared with differential operation) is acceptable.
Input Common Mode Voltage
The allowable input common mode voltage (V
CM
) range depends upon V
A
and V
REF
used for the ADC161S626.
The ranges of V
CM
are depicted in Figure 40 and Figure 41. Note that these figures only apply to a V
A
of 5V.
Equations for calculating the minimum and maximum V
CM
for differential and single-ended operations are shown
in Table 1.
Figure 40. V
CM
range for Differential Input operation
Figure 41. V
CM
range for single-ended operation
Table 1. Allowable V
CM
Range
Input Signal Minimum V
CM
Maximum V
CM
Differential V
REF
/ 2 V
A
V
REF
/ 2
Single-Ended V
REF
V
A
V
REF
CMRR
By using this differential input, small signals common to both inputs are rejected. As shown in Figure 42, noise is
immune at low frequencies where the common-mode rejection ratio (CMRR) is 90 dB. As the frequency
increases to 1 MHz, the CMRR rolls off to 40 dB . In general, operation with a fully differential input signal or
voltage will provide better performance than with a single-ended input. However, if desired, the ADC161S626
can be presented with a single-ended input.
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