THS10064_09 Datasheet, PDF (34/42 Pages) Texas Instruments – 10-BIT, 4 ANALOG INPUT, 6 MSPS, SIMULTANEOUS SAMPLING ANALOG-TO-DIGITAL CONVERTER

THS10064
SLAS255B – DECEMBER 1999 – REVISED DECEMBER 2002
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A differential operation is desired for many applications. Figure 43 shows a simplified model for the analog inputs
AINM and AINP, which are configured for differential operation. This configuration has a few advantages, which are
discussed in the following paragraphs.
AINP
AINM
VREFP
+
Σ ^VADC
–
10-Bit
ADC
VREFM
Figure 43. Differential Input Stage
In comparison to the single-ended configuration it can be seen that the voltage, V_ADC, which is applied at the input
of the ADC is the difference between the input AINP and AINM. This means that V_REFM defines the minimum voltage
(V_ADC) which can be applied to the ADC. V_REFP defines the maximum voltage (VADC) which can be applied to the
ADC. The voltage V_ADC can be calculated as follows:
+ VADC ABS(AINP–AINM)
(2)
An advantage to single-ended operation is that the common-mode voltage
+ ⁾ VCM
AINM AINP
2
(3)
can be rejected in the differential configuration, if the following condition for the analog input voltages is true:
v v AGND AINM, AINP AVDD
(4)
v v 1 V VCM 4 V
(5)
In addition to the common-mode voltage rejection, the differential operation allows a dc-offset rejection which is
common to both analog inputs. See Figure 45.
SINGLE-ENDED MODE OF OPERATION
The THS10064 can be configured for single-ended operation using dc- or ac-coupling. In either case, the input of
the THS10064 must be driven from an operational amplifier that does not degrade the ADC performance. Because
the THS10064 operates from a 5-V single supply, it is necessary to level-shift ground-based bipolar signals to comply
with its input requirements. This can be achieved with dc- and ac-coupling. An application example is shown for
dc-coupled level shifting in the following section, dc-coupling.
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