THS7327 Datasheet, PDF (15/26 Pages) Texas Instruments – 3-Channel RGBHV Video Buffer with I2C Control, Selectable Filters, Monitor Pass-Thru,2:1 Input MUX, and Selectable Input Bias Modes

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THS7327
SLOS502 – SEPTEMBER 2006
APPLICATION INFORMATION (continued)
INPUT OVERVOLTAGE PROTECTION
The THS7327 is built using a high-speed complementary bipolar and CMOS process. The internal junction
breakdown voltages are relatively low for these very small geometry devices. These breakdowns are reflected in
the Absolute Maximum Ratings table. All input and output device pins are protected with internal ESD protection
diodes to the power supplies, as shown in Figure 8.
V_S+
External
Input/
Output
Pin
Internal
Circuitry
Figure 8. Internal ESD Protection
These diodes provide moderate protection to input overdrive voltages above and below the supplies. The
protection diodes can typically support 30-mA of continuous current when overdriven.
TYPICAL CONFIGURATION
The THS7327 is typically used as a video buffer driving a video ADC (such as the TVP7001) with 0dB gain and
the monitor output path drives an output line with 6-dB gain along with horizontal (H) and vertical (V) sync
signals. The versatility of the THS7327 allows virtually any video signal to be utilized. This includes
standard-definition (SD), enhanced-definition (ED), and high-definition (HD) Y’P’_BP’_R (sometimes labeled Y’U’V’
or incorrectly labeled Y’C’_BC’_R) signals, S-Video Y’/C’ signals, and the composite video baseband signal (CVBS)
of a SD video system. These signals can also be R’G’B’ (or G’B’R’) or other variations on the placement of the
sync signals commonly called R’G’sB’ (sync on Green) or R’sG’sB’s (sync on all signals). Additionally, the
THS7327 handles the digital H and V sync signals with the noise immunity enhancement of a schmitt trigger.
This schmitt trigger defaults to 1.45V, but can be set externally to be anywhere form 0.9V to 2.0V for added
flexibility.
Simple control of the I²C configures the THS7327 for any configuration conceivable. For example, the THS7327
can be configured to have Channel 1 Input connected to input A while Channels 2 and 3 could be connected to
input B. See the multiple application notes sections explaining the I²C interface later in this document on how to
configure these options.
Note that the Y’ term is used for the luma channels throughout this document rather than the more common
luminance (Y) term. This is to account for the true 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 true luminance (Y) is not maintained and hence the 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 non-linear. True chominance (C) is derived from linear RGB and hence 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 non-linear (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'
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