AD9943/AD9944

Rev. B | Page 16 of 20

A/D CONVERTER

The ADC uses a 2 V input range. Better noise performance

results from using a larger ADC full-scale range. The ADC uses

a pipelined architecture with a 2 V full-scale input for low noise

performance.

VARIABLE GAIN AMPLIFIER

The VGA stage provides a gain range of 6 dB to 40 dB,

programmable with 10-bit resolution through the serial digital

interface. The minimum gain of 6 dB is needed to match a 1 V

input signal with the ADC full-scale range of 2 V. A plot of the

VGA gain curve is shown in Figure 13.

()

(

)

dB

3

.

5

dB

035

.

0

dB

+

×

=

Code

VGA

Gain

VGA

VGA GAIN REGISTER MODE

42

12

383

127

0

30

255

36

34

18

6

511

639

767

895

1023

Figure 13. VGA Gain Curve