WM8216

Production Data

w

PD Rev 4.0 March 2007

13

Figure 7 RLC Clamp Control Options

When an input waveform has a stable reference level on every pixel it may be desirable to clamp

every pixel during this period. Setting CLMPCTRL=0 means that the RLC switch is closed whenever

the RSMP input pin is high, as shown in Figure 8.

MCLK

VSMP

RSMP

RLC switch control

"CLMP"

(RLCEN=1,CLMPCTRL=0)

RLC switch closed

when RSMP=1

Video sample taken on

fallling edge of VSMP

Reset/reference sample taken

on fallling edge of RSMP

INPUT VIDEO

SIGNAL

reference

("black") level

video level

Figure 8 Reset Level Clamp Operation (CLMPCTRL=0), CDS operation shown, non-CDS also possible

In situations where the input video signal does not have a stable reference level it may be necessary

to clamp only during those pixels which have a known state (e.g. the dummy, or “black” pixels at the

start or end of a line on most image sensors). This is known as line-clamping and relies on the input

capacitor to hold the DC level between clamp intervals. However, it should be noted that in non-CDS

mode, this method of operation will result in a slow drift in the output codes. In non-CDS mode

(CDS=0) line clamping can be done directly by controlling the RSMP input pin to go high during the

black pixels only.

Alternatively it is possible to use RSMP to identify the black pixels and enable the clamp at the same

time as the input is being sampled (i.e. when VSMP is high and RSMP is high).

This mode is

enabled by setting CLMPCTRL=1 and the operation is shown in Figure 9.