WM8199

Production Data

w

PD Rev 3.2 November 2003

14

MCLK

VSMP

VS

R

R

R

R

Figure 10 Reset Sample and Clamp Timing

For CIS type sensor signals, non-CDS processing is used. In this case, the video level is processed

with respect to the voltage on pin VRLC/VBIAS, generated internally or externally as described

mode.

OFFSET ADJUST AND PROGRAMMABLE GAIN

The output from the CDS block is a differential signal, which is added to the output of an 8-bit Offset

DAC to compensate for offsets and then amplified by an 8-bit PGA. The gain and offset for each

channel are independently programmable by writing to control bits DAC[7:0] and PGA[7:0].

The gain characteristic of the WM8199 PGA is shown in Figure 11. Figure 12 shows the maximum

device input voltage that can be gained up to match the ADC full-scale input range (3V).

0

1

2

3

4

5

6

7

8

0

64

128

192

256

Gain register value (PGA[7:0])

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0

64

128

192

256

Gain register value (PGA[7:0])

Figure 11 PGA Gain Characteristic

Figure 12 Peak Input Voltage to Match ADC Full-scale Range

In colour line-by-line mode the gain and offset coefficients for each colour can be multiplexed in order

(Red

→ Green → Blue → Red…) by pulsing the ACYC/RLC pin, or controlled via the FME,

ACYCNRLC and INTM[1:0] bits. Refer to the Line-by-Line Operation section for more details.

ADC INPUT BLACK LEVEL ADJUST

The output from the PGA should be offset to match the full-scale range of the ADC (3V). For

negative-going input video signals, a black level (zero differential) output from the PGA should be

offset to the top of the ADC range by setting register bits PGAFS[1:0]=10. For positive going input

signal the black level should be offset to the bottom of the ADC range by setting PGAFS[1:0]=11.

Bipolar input video is accommodated by setting PGAFS[1:0]=00 or PGAFS[1:0]=01 (zero differential

input voltage gives mid-range ADC output).