THS1040

SLAS290C − OCTOBER 2001 − REVISED OCTOBER 2004

22

www.ti.com

PRINCIPLES OF OPERATION

operating configuration examples (continued)

Figure 30 shows a configuration using the internal ADC references for digitizing a dc-coupled differential input

If a transformer is used to generate the differential ADC input from a single-ended signal, then the BIASREF

AIN+

AIN−

VREF = 0.75 V

REFB

MODE

REFSENSE

AVDD

1.875 V

1.125 V

1.875 V

1.125 V

1.5 V

1.5 V

REFT

5 k

Ω

10 k

Ω

0.1

µF

10

µF

20 pF

20 pF

20

Ω

20

Ω

0.1

µF

0.1

µF

10

µF

Figure 30. Operating Configuration: 1.5-V Differential Input, Internal ADC References

Figure 31 shows a configuration using the internal ADC references and an external VREF source for digitizing

a dc-coupled single-ended input with span 0.5 V to 2 V. A 1.25-V external source provides the bias voltage for

the AIN− pin and also, via a buffered potential divider, the 0.75 VREF voltage required to set the input range

AIN+

AIN−

REFT

MODE

REFB

2 V

0.5 V

1.25 V

VREF

AVDD

10 k

Ω

_

+

REFSENSE

AVDD

15 k

Ω

(0.75 V)

1.25

Source

0.1

µF

10

µF

0.1

µF

0.1

µF

20 pF

20 pF

20

Ω

20

Ω

10

µF

Figure 31. Operating Configuration: 1.5-V Single-Ended Input, External VREF Source