15
ICS2008B
ICS2008B
Applications
Crystal Oscillator
This oscillator will operate
properly with either a serial or
parallel resonant crystal. If fre-
quency accuracy is critical,
a parallel resonant crystal is
recommended.
Threshold Bypass Pins
These pins provide access to the internal references for clamp
level (CTHRESH), SYNC slicer (STHRESH), and data slicer
(DTHRESH). In general, these pins are left open, and the levels
are output. However, should the user want to set other levels,
these pins can be over-driven with the desired threshold
level(s).
CTHRESH is the threshold
to which the input video
sync tips are clamped. The
CTHRESH level is nomi-
nally 1.3V. With the
incoming video riding on
this 1.3V DC level, the in-
ternal SYNC separator
sizes the video at 20 IRE up
from the SYNC tips. This
level, STHRESH, is nomi-
nally 0.14V above
CTHRESH. The SYNC separator ignores short pulses which
fall below the STHRESH level such as these that come from the
chroma component of the video. DTHRESH is the data slicer
reference. It is nominally 0.57V above CTHRESH.
Video Inputs
Y1, Y2, C1 and C2 pins
must be capacitively
coupled to the terminated
video source(s). These in-
puts are clamped to the
CTHRESH level. A typi-
cal coupling capacitance
is 0.1µF.
Video Outputs
YOUT and COUT are
outputs of analog multi-
plexers which select the
video source from Y1,
C1 or Y2, C2. These
outputs are not buffered,
so minimizes signal dis-
tortion. It is, therefore,
important to keep the ca-
pacitive and resistive
load on the YOUT and
COUT pins to a mini-
mum. If DC coupling is desired, the plus input of the opamp
should be high impedance with a low bias current, and its out-
put should be able to drive a 75 ohm load with an appropriate
video bandwidth. In general, composite NTSC and S-video
signals have a bandwidth of 4.2 MHz. A minimum output
buffer bandwidth of 10 MHz is recommended. Care should
be taken in board layout to minimize stray capacitance on the
YOUT and COUT pins. Otherwise, there could be high fre-
quency roll-off which could result in a loss of chrominance
amplitude.
Self Biased Inputs
The CLICK and FRAME inputs are biased to 1/3 VDD and
connected to plus inputs of two comparators. The minus
inputs are internally biased to 1/3 VDD. When CLICK or
FRAME sources are ana-
log, they should be
capacitively coupled to the
input pin. However, if the
sources are digital, they
may be tied to the pins di-
rectly. It is important to
make sure that the digital
levels into these pins swing
above and below the 1/3
VDD threshold of the com-
parators. This is not a
problem with digital CMOS
sources, but it could be
with TTL sources.
LTCIN+ and LTCIN
–
are
comparator inputs for the
LTC input. This differential
input is provided to maximize noise immunity. If the LTC
source is single ended, the LTCIN
–
should be capacitively
coupled to the ground reference of that source. If the LTC
source is digital, set the LTCIN
–
to the desired threshold, and
connect the digital source to LTCIN+.
Fig. 4 - Crystal Oscillator
Fig. 5 – Threshold Bias
Fig. 6 – S-Video Input
Fig. 7 - Video Output
Fig. 8 - Self Biased Inputs
