9600 Service Manual - gmecorp-usa.com

32 Image System
PIXEL/COLUMN FILTER PCB
Asy. #00-878047 - Sch. #878045
The Pixel/Column Filter PCB is mounted on the CCD camera assembly (see Figures 1
and 22). The video signal from the camera passes through the circuitry on this PCB and
then on to the Workstation image processor. The Pixel/Column Filter PCB has two
functional sections; a column artifact cancellation filter and a pixel artifact filter. The pixel
filter section filters out noise from the camera video that appears as white pixels in the
image. The column filter circuitry is used to cancel out inherent blemishes of the CCD
sensor that appear as columns in the image.
NOTE: Some systems may have a Pixel Filter PCB instead of a Pixel/Column Filter
PCB. The main difference is the lack of column filter circuitry on the Pixel
Filter PCB. Later systems may have neither of these PCBs. Also, a -03
revision Image Function PCB must be used with the Pixel/Column Filter
PCB. Systems with S/N 69-2001 and higher are expected to have the Pixel
Filter PCB only.
Pixel Filter Circuitry
The Pixel Filter section of the PCB is comprised of U4, Q1 and the interconnecting
resistors. The circuitry was designed to attenuate pixel blemishes (noise) from the output
(P2) of the CCD Camera. The video signal from the CCD camera enters at J1 and is
applied to the base of transistor Q1 at pin 2. The signal is also routed through a 60 nS
delay IC U4. The 60 nS delayed video signal is applied to the base of transistor Q1 at
pin 6. Both transistors are wired to function as emitter followers. In order to match the
transistor’s characteristics, both transistors are located on the same integrated circuit die
(Q1). The emitters of the two transistors are connected to the output resistor R12. The
video output signal becomes the more negative voltage of either the delayed or nondelayed
video signal. Thus any positive noise glitches (or white pixels) are attenuated as
shown in Figure 18 below. The resultant video signal is sent to the Workstation via the
Motherboard and the Interconnect Cable.
Power (+5 VDC) is supplied to the Pixel Filter portion of the PCB by the camera (+5P) at
J3 pin 6. It is filtered by series resistor R11 and capacitors C10 and C11 to decrease the
potential of noise entering the PCB through the power supply.
VIDEO INPUT
NORMAL AND DELAYED
VIDEO OUTPUT
NOISE
GLITCH
Figure 18 - Noise Filtering Function of Pixel Filter Circuitry