THS7314EVM Datasheet, PDF (12/31 Pages) Texas Instruments – 3-Channel SDTV Video Amplifier With 5th-Order Filters and 6-dB Gain

THS7314
SLOS513A – DECEMBER 2006 – REVISED MARCH 2011
+ Vs
External
Input/
Output
Pin
Internal
Circuitry
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Figure 28. Internal ESD Protection
These diodes provide moderate protection to input overdrive voltages above and below the supplies as well. The
protection diodes can typically support 30-mA of continuous current when overdriven.
TYPICAL CONFIGURATION and VIDEO TERMINOLOGY
A typical application circuit using the THS7314 as a video buffer is shown in Figure 29. It shows a DAC (or
encoder such as the THS8200) driving the three input channels of the THS7314. Although the S-Video Y'C'
channels and the Composite video channel of a Standard Definition video (SD) system are shown, these
channels can easily be the Y'P'_BP'_R (sometimes labeled Y'U'V' or incorrectly labeled Y'C'_BC'_R) signals of a 480i or
576i system. These signals can also be G'B'R' (R'G'B') signals or other variations.
Note that the Y' term is used for the luma channels throughout this document rather than the more common
luminance (Y) term. The reason is to account for the definition of luminance as stipulated by the CIE –
International Commission on Illumination. Video departs from true luminance since a nonlinear term, gamma, is
added to the true RGB signals to form R'G'B' signals. These R'G'B' signals are then used to mathematically
create luma (Y'). Thus luminance (Y) is not maintained providing a difference in terminology.
This rationale is also used for the chroma (C') term. Chroma is derived from the non-linear R'G'B' terms and thus
it is nonlinear. Chominance (C) is derived from linear RGB giving the difference between chroma (C') and
chrominance (C). The color difference signals (P'_B / P'_R / U' / V') are also referenced this way to denote the
nonlinear (gamma corrected) signals.
R'G'B' (commonly mislabeled RGB) is also called G’B’R’ (again commonly mislabeled as GBR) in professional
video systems. The SMPTE component standard stipulates that the luma information is placed on the first
channel, the blue color difference is placed on the second channel, and the red color difference signal is placed
on the third channel. This is consistent with the Y'P'_BP'_R nomenclature. Because the luma channel (Y') carries the
sync information and the green channel (G') also carries the sync information, it makes logical sense that G' be
placed first in the system. Since the blue color difference channel (P'_B) is next and the red color difference
channel (P'_R) is last, then it also makes logical sense to place the B' signal on the second channel and the R'
signal on the third channel respectfully. Thus hardware compatibility is better achieved when using G'B'R' rather
than R'G'B'. Note that for many G'B'R' systems sync is embeded on all three channels, but may not always be
the case in all systems.
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