Datasheet

LMH1980
www.ti.com SNLS263A –JULY 2007–REVISED MARCH 2013
APPLICATION INFORMATION
GENERAL DESCRIPTION
The LMH1980 is designed to extract the timing information from various video formats with standard and non-
standard vertical serration and output the syncs and relevant timing signals in CMOS logic. Its advanced features
and easy application make it ideal for consumer, professional, and industrial video systems where sync timing
needs to be extracted from SD, HD, and PC video signals. The device can operate from a supply voltage
between 3.3V and 5V. The only required external components are bypass capacitors between the V
CC
and GND
pins, input coupling capacitor (C
IN
) from the signal source to the V
IN
pin, and a fixed-value 1% precision resistor
between the R
EXT
and GND pins. Refer to the test circuit in Figure 2.
R
EXT
Resistor
The precision external resistor (R
EXT
) establishes the internal bias current and precise reference voltage for the
LMH1980. For optimal performance, R
EXT
should be a 10 kΩ 1% precision resistor with a low temperature
coefficient to ensure proper operation over a wide temperature range. Using a R
EXT
resistor with less precision
may result in reduced performance (like worse performance, increased propagation delay variation, or reduced
input sync amplitude range) against temperature, supply voltage, input signal, or part-to-part variations.
NOTE
The R
EXT
resistor used with the LMH1980 serves a different function than the “R
SET
resistor” used with other previous sync separators, like the LM1881. For the LM1881, the
R
SET
value needed to be adjusted externally to support different input line rates. For the
LMH1980, the R
EXT
value is fixed, and the device automatically detects the input line rate
to support various video formats without electrical or physical intervention.
Automatic Format Detection and Switching
Automatic format detection eliminates the need for adjusting an external R
SET
resistor or programming via a
microcontroller. The device outputs will respond correctly to a switch in video format after a sufficient start-up
time has been satisfied, usually within 1 to 2 fields of video. Unlike other sync separators, the LMH1980 does not
require the power to be cycled in order to produce correct outputs after a significant change to the input signal.
See START-UP TIME for more details.
Fixed-Level Sync Slicing
The LMH1980 uses fixed-level sync slicing for video inputs with an amplitude from 0.5V
PP
to 2V
PP
, which allows
for proper sync separation even for improperly terminated or attenuated input signals. The fixed-level sync slicing
threshold is nominally 70 mV above the clamped sync tip. This means that for a minimum video input signal
amplitude of 0.5V
PP
, the slicing level is near the mid-point of the sync pulse amplitude. This slicing level is
independent of the input signal amplitude; therefore, for a 2V
PP
input, the slicing level occurs at 12% of the sync
pulse amplitude.
INPUT CONSIDERATIONS
The LMH1980 supports sync separation for analog CVBS, Y (luma) from Y/C and YP
B
P
R
, and G (sync on green)
from GBR/RGsB, as specified in the following video standards.
• Composite Video (CVBS) and S-Video (Y/C):
– SMPTE 170M (NTSC), ITU-R BT.470 (PAL)
• Component Video (YP
B
P
R
/GBR):
– SDTV: SMPTE 125M, SMPTE 267M, ITU-R BT.601 (480I, 576I)
– EDTV: ITU-R BT.1358 (480P, 576P)
– HDTV: SMPTE 296M (720P), SMPTE 274M (1080I/P), SMPTE RP 211 (1080PsF)
• PC Graphics (RGsB):
– VESA Monitor Timing Standards and Guidelines Version 1.0, Revision 0.8
•
Non-Standard Video:
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