CS7622

12

DS322PP1

would be “1100000000000.” The transfer function

of the Vin/gain adjust out is shown in Figure 11.

A block diagram of the gain adjust block is shown

in Figure 12.

Since the analog gain changes do not match the

digital shifts exactly, there is a potential to have

non-monotonic digital output. In order to remove

this problem, calibration is performed. During cal-

ibration, offset values are found that will be used to

counteract the errors caused by the analog gain

mismatch. Using these offset values, the final out-

put is a monotonic continuous 13-bit value.

3.4 13-to-10 Bit Compander

While a 13 bit output may be useful in some appli-

cations, others may require the standard 10 bit out-

put. To accommodate this and yet still retain the

advantages of the increased dynamic range, a 13-

to-10 (or 13-to-12) bit compander is included. By

using the picture content as a guide, the user can se-

lect which curve will lead to the best overall dy-

namic range in the picture. The Companding

module takes 13-bit data as input, and outputs ei-

ther 10-bit companded data, 12-bit MSB-clipped

data or it lets the original 13-bit data pass through.

By programming the compander in the way that is

shown in Figure 13, it is possible to compensate for

DIG ADJUST OUT (13 BITS)

VIN (V)

1.0

0.5

0.25

0.125

8192

4096

1X

2X

4X

8X

ADC OUTPUT

00

01

10

11

1024

2048

0

Figure 11. Transfer function of Vin to Gain Adjust output Block (assuming full scale level of 1.0 V)

GAIN ADJUST

SHIFT BY 0,1,2, OR 3

ADC OUTPUT

10

2

VGA_ADC OUTPUT

TO DIGITAL GAIN

13

Figure 12. Gain Adjust output Block