WM8198

Production Data

w

PD Rev 4.0 June 2004

14

MCLK

VSMP

VS

R

R

R

R

Figure 8 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; non-CDS processing is achieved by setting switch 2 in the lower position, CDS = 0.

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 a Programmable Gain Amplifier. The 9-bit

PGA can operate in two modes, a wide gain range (linear on a dB scale) mode or a high resolution

(linear in V/V) mode. The PGA mode is selected by setting the register bit PGAMODE. The default

setting is PGAMODE=0 which selects the wide gain range mode. Figure 9 and Figure 10 show the

transfer functions of the PGA in each mode. The gain and offset for each channel are independently

programmable by writing to control bits DAC[7:0] and PGA[8:0].

Figure 9 Wide Range Gain Mode (PGAMODE=0)

Figure 10 High-Res Gain Mode (PGAMODE=1)

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.

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0

128

256

384

512

Gain register code (PGA[8:0])

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0

128

256

384

512

Gain Register Code (PGA[8:0])