THS10064 Datasheet, PDF(30/41 Page) Texas Instruments – 10-BIT 6 MSPS, SIMULTANEOUS SAMPLING ANALOG-TO-DIGITAL CONVERTER

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THS10064 Datasheet, PDF (30/41 Pages) Texas Instruments – 10-BIT 6 MSPS, SIMULTANEOUS SAMPLING ANALOG-TO-DIGITAL CONVERTER

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THS10064

10-BIT 6 MSPS, SIMULTANEOUS SAMPLING

ANALOG-TO-DIGITAL CONVERTER

SLAS255 â DECEMBER 1999

analog input configuration and reference voltage (continued)

A differential operation is desired for many applications. Figure 18 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

Î£ VADC

10-Bit

ADC

VREFM

Figure 18. Differential Input Stage

In comparison to the single-ended configuration it can be seen that the voltage, VADC, which is applied at the

input of the ADC is the difference between the input AINP and AINM. This means that VREFM defines the

minimum voltage (VADC) which can be applied to the ADC. VREFP defines the maximum voltage (VADC) which

can be applied to the ADC. The voltage VADC can be calculated as follows:

+ VADC ABS(AINPâAINM)

(2)

The voltage VADC has to satisfy the following condition:

v v VREFM VADC VREFP

(3)

An advantage to single-ended operation is that the common-mode voltage

+ ) VCM

AINM AINP

(4)

can be rejected in the differential configuration, if the following condition for the analog input voltages is true:

v v AGND AINM, AINP AVDD

(5)

v v 1 V VCM 4 V

(6)

In addition to the common-mode voltage rejection, the differential operation allows a dc-offset rejection which

is common to both analog inputs. See also Figure 20.

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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