THS1401-EP THS1403-EP THS1408-EP

14-BIT, 1/3/8 MSPS DSP COMPATIBLE ANALOG-TO-DIGITAL CONVERTERS

WITH INTERNAL REFERENCE AND PGA

SGLS129A – JULY 2002 – REVISED NOVEMBER 2002

17

POST OFFICE BOX 655303

APPLICATION INFORMATION

driving the analog input

The THS1401/3/8 ADCs have a fully differential input. A differential input is advantageous with respect to SNR,

SFDR, and THD performance because the signal peak-to-peak level is 50% of a comparable single-ended input.

There are three basic input configurations:

fully differential configuration

In this configuration, the ADC converts the difference (

∆IN) of the two input signals on IN+ and IN–.

100 pF

IN+

IN–

THS1401/3/8

22

Ω

100 pF

22

Ω

Figure 19. Differential Input

The resistors and capacitors on the inputs decouple the driving source output from the ADC input and also serve

as first order low pass filters to attenuate out of band noise.

positive full-scale output is reached, if

∆IN equals ∆REF, the negative full-scale output is reached, if ∆IN equals

–

∆REF.

∆IN [V]

OUTPUT

–

∆REF

– full scale

0

0

∆REF

+ full scale