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TYPICAL CONFIGURATION and VIDEO TERMINOLOGY

THS7313

SLOS483 – NOVEMBER 2005

APPLICATION INFORMATION (continued)

Figure 46. 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.

A typical application circuit using the THS7313 as a video buffer is shown in Figure 47. It shows a DAC (or

encoder such as the THS8200) driving the three input channels of the THS7313. Although the S-Video Y' and C'

channels and the composite video baseband signal (CVBS) channel of a standard definition video (SD) system

are shown, these channels can also 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 could be G’B’R’ (R'G'B') signals or other variations. Note that for

computer signals the sync should be embedded within the signal for a system with only 3-outputs. This is

sometimes labeled as R’G’sB’ (sync on green) or R’sG’sB’s (sync on all signals).

The second set of inputs (B-Channels) shown are being driven from an external input typically used as a

pass-through function. These are traditional SD or professional G’B’R’ video signals. The THS7313’s flexibility

allows for almost any input signal to be driven into the THS7313 regardless of the other set of inputs. Control of

the I2C configures the THS7313. For example, the THS7313 can be configured to have Channel 1 Input

connected to input A while Channels 2 and 3 are connected to input B. The various sections explaining the I2C

interface later in this data sheet.

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 GBR signals to form G’B’R’ signals. These G’B’R’ 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 nonlinear G’B’R’ terms and thus

it is nonlinear. Chominance (C) is derived from linear GBR 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; however, this may not be

true in all systems.

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