wm8215 Wolfson Microelectronics plc, wm8215 Datasheet - Page 14

• Manufacturer Part Number: wm8215
• Description: 60msps 10-bit 3-channel Ccd Digitiser
• Manufacturer: Wolfson Microelectronics plc

WM8215
RESET LEVEL CLAMPING (RLC)
Figure 9 Reset Level Clamp Operation (CLAMPCTRL=0), CDS operation shown, non-CDS also possible
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(RLCEN=1,CLMPCTRL=0)
RLC switch control
INPUT VIDEO
"CLMP"
SIGNAL
MCLK
VSMP
RSMP
To ensure that the signal applied to the WM8215 lies within the supply voltage range (0V to AVDD)
the output signal from a CCD is usually level shifted by coupling through a capacitor, C
circuit clamps the WM8215 side of this capacitor to a suitable voltage through a CMOS switch during
the CCD reset period (pixel clamping) or during the black pixels (line clamping). In order for clamping
to produce correct results the input voltage during the clamping must be a constant value.
The WM8215 allows the user to control the RLC switch in a variety of ways as illustrated in Figure 8
This figure shows a single channel, however all 3 channels are identical, each with its own clamp
switch controlled by the common CLMP signal.
The method of control chosen depends upon the characteristics of the input video. The RLCEN
register bit must be set to 1 to enable clamping, otherwise the RLC switch cannot be closed (by
default RLCEN=1).
Note that unused inputs should be left floating, or grounded through a decoupling capacitor, if reset
level clamping is used.
Figure 8 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.
whenever the RSMP input pin is high, as shown in Figure 9.
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
Video sample taken on
fallling edge of VSMP
reference
("black") level
Reset/reference sample taken
on fallling edge of RSMP
RLC switch closed
when RSMP=1
video level
Setting CLAMPCTRL=0 means that the RLC switch is closed
PD, Rev 4.2, February 2009
Production Data
IN.
The RLC
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