WM8198

Production Data

w

PD Rev 4.0 June 2004

13

TIMING CONTROL

S/H

4-BIT

RLC DAC

CL

+

+

-

TO OFFSET DAC

RLC

CDS

FROM CONTROL

INTERFACE

S/H

V

S

R

S

FROM CONTROL

INTERFACE

MCLK

VSMP

RLC/ACYC

INPUT SAMPLING

BLOCK FOR RED

CHANNEL

CDS

C

IN

RINP

VRLC/

VBIAS

2

1

EXTERNAL VRLC

VRLCEXT

Figure 6 Reset Level Clamping and CDS Circuitry

If auto-cycling is not required, RLC can be selected by pin RLC/ACYC.

Figure 7 illustrates control of RLC for a typical CCD waveform, with CL applied during the reset

period.

The input signal applied to the RLC/ACYC pin is sampled on the positive edge of MCLK that occurs

during each VSMP pulse. The sampled level, high (or low) controls the presence (or absence) of the

internal CL pulse on the next reset level. The position of CL can be adjusted by using control bits

CDSREF[1:0] ().

If auto-cycling is required, pin RLC/ACYC is no longer available for this function and control bit

RLCINT determines whether clamping is applied.

Figure 7 Relationship of RLC Pin, MCLK and VSMP to Internal Clamp Pulse, CL

The VRLC/VBIAS pin can be driven internally by a 4-bit DAC (RLCDAC) by writing to control bits

RLCV[3:0]. The RLCDAC range and step size may be increased by writing to control bit

RLCDACRNG. Alternatively, the VRLC/VBIAS pin can be driven externally by writing to control bit

VRLCEXT to disable the RLCDAC and then applying a d.c. voltage to the pin.

CDS/NON-CDS PROCESSING

For CCD type input signals, the signal may be processed using CDS, which will remove pixel-by-pixel

common mode noise. For CDS operation, the video level is processed with respect to the video reset

level, regardless of whether RLC has been performed. To sample using CDS, control bit CDS must

be set to 1 (default), this sets switch 2 into the position shown in Figure 6 and causes the signal

reference to come from the video reset level. The time at which the reset level is sampled, by clock

MCLK

VSMP

ACYC/RLC

or RLCINT

CL

(CDSREF = 01)

INPUT VIDEO

1X

X

0

X

X

0

RGB

RGB

No RLC on this Pixel

RLC on this Pixel

Programmable Delay

RGB