THS1007

SLAS286A – AUGUST 2000– REVISED DECEMBER 2002

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ANALOG INPUT CONFIGURATION AND REFERENCE VOLTAGE

The THS1007 features four analog input channels. These can be configured for either single-ended or

differential operation. Figure 38 shows a simplified model, where a single-ended configuration for channel AINP

reference voltage). The resulting analog input voltage swing of 2 V can be expressed by:

V

REFM v

AINP

v V

REFP

(1)

10-Bit

ADC

VREFP

VREFM

AINP

Figure 38. Single-Ended Input Stage

A differential operation is desired in many applications due to a better signal-to-noise ration. Figure 39 shows

a simplified model for the analog inputs AINM and AINP, which are configured for differential operation. The

differential operation mode provides in terms of performance benefits over the single-ended mode and is

therefore recommended for best performance. The THS1007 offers 2 differential analog inputs and in the

single-ended mode4 analog inputs. If the analog input architecture is different, common-mode voltages can be

rejected. Additional details for both modes are given below.

10-Bit

ADC

VREFP

VREFM

AINP

Σ

VADC

AINM

+

–

Figure 39. Differential Input Stage

follows:

V

ADC +

ABS(AINP–AINM)

(2)

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

(3)

V

CM +

AINM

) AINP

2

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

(4)

AGND

v AINM, AINP v AV

DD

(5)

1V

v V

CM v

4V

SINGLE-ENDED MODE OF OPERATION

The THS1007 can be configured for single-ended operation using dc or ac coupling. In either case, the input

of the THS1007 must be driven from an operational amplifier that does not degrade the ADC performance.

Because the THS1007 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.