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INPUT OVERVOLTAGE PROTECTION

External

Input/

Output

Pin

Internal

Circuitry

V

S+

TYPICAL CONFIGURATION

THS7347

SLOS531 – MAY 2007

APPLICATIONS INFORMATION (continued)

The THS7347 is built using a very 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 3.

Figure 3. 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 usng the THS7347 as an ac-coupled input video buffer is shown in Figure 4. It shows

the THS7347 driving a video ADC (such as the TVP7000) with 0-dB gain and also driving an output line with

6-dB gain. The Horizontal and Vertical Sync signals are also driven to the ADC and the Monitor Output

separately. Although the computer resolution R’G’B’HV signals are shown, these channels can easily be the

composite video baseband signal (CVBS). Note that the R’G’B’ channels could be professional/broadcast G’B’R’

signals or other R’G’B’ variations based on the placement of the sync signals that are commonly called R’G’sB’

(sync on Green) or R’sG’sB’s (sync on all signals).

The second set of inputs (B-Channels) shown are connected to another set of inputs. Again, these inputs can be

either HD, ED, SD, or R'G'B'/G'B'R' video signals. The THS7347 flexibility allows for virtually any input signal to

THS7347 for any conceivable combination. For example, the THS7347 can be configured to have Channel 1

Input connected to input A while Channel 2 and Channel 3 are connected to input B. See the multiple application

Note that the Y' term is used for the luma channels throughout this document, rather than the more common

luminance (Y) term. The reason for this usage is to account for the true definition of luminance as stipulated by

the CIE (International Commission on Illumination). Video departs from true luminance because a nonlinear

term, gamma, is added to the true RGB signals to form R'G'B' signals. These R'G'B' signals are then utilized to

mathematically create luma (Y'). Therefore, true luminance (Y) is not maintained, and thus the difference in

terminology arises.

This rationale is also utilized for the chroma (C') term. Chroma is derived from the nonlinear R'G'B' terms and

therefore it is also nonlinear. True chominance (C) is derived from linear RGB, and thus the difference between

to denote the nonlinear (gamma-corrected) signals.

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