THS0842

DUAL-INPUT, 8-BIT, 40 MSPS LOW-POWER ANALOG-TO-DIGITAL CONVERTER

WITH SINGLE OR DUAL PARALLEL BUS OUTPUT

SLAS246 – DECEMBER 1999

20

POST OFFICE BOX 655303

PRINCIPLES OF OPERATION

analog input (continued)

1.5 V

I/Q+

1.5 + 0.25 V

I/Q+

1.5 – 0.25 V

Positive

Analog

Input

1.5 V

I/Q–

1.5 – 0.25 V

I/Q–

1.5 + 0.25 V

Negative

Analog

Input

0 V

+0.5 V

Differential

Input

–0.5 V

1.0 Vp–p

Figure 19. Differential Input Waveform

The analog input can be dc coupled (Figure 21) as long as the inputs are within the analog input common mode

voltage range. The resistors, R, in Figure 21 are not absolutely necessary but may be used as load setting

resistors. A capacitor, C, connected from I/Q IN+ to I/Q IN– will help filter any high frequency noise on the inputs,

also improving performance. Note, that the chosen value of capacitor C must take into account the highest

frequency component of the analog input signal.