+2.6Vto+5V

Enable

75 W

Out1

Channel1

R

75 W

LPF

3Pole

20MHz

6dB

x2

Level

Shift

Out2

Channel2

R

75 W

75 W

LPF

3Pole

20MHz

6dB

x2

Level

Shift

Channel3

R

Out3

75 W

75 W

LPF

3Pole

20MHz

6dB

x2

Level

Shift

+V

S

External

Input/Output

Pin

Internal

Circuitry

THS7320

www.ti.com

SBOS565B – JULY 2011 – REVISED SEPTEMBER 2012

VIDEO INPUT OVERVOLTAGE PROTECTION

The THS7320 is built using a very high-speed, complementary, bipolar 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 electrostatic

discharge (ESD) protection diodes to the power supplies, as shown in Figure 55.

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.

Figure 55. Internal ESD Protection For Video Section

TYPICAL VIDEO CONFIGURATION AND VIDEO TERMINOLOGY

A typical application circuit using the THS7320 as a video buffer is shown in Figure 56. It shows a DAC or

encoder dc-coupled to the input channels of the THS7320 and the output of the THS7320 dc-coupled to the

video line. These signals can be NTSC, PAL, or SECAM signals including composite video baseband signal

Figure 56. Typical THS7320 Video Section with DC-Coupled Encoder/DAC and DC-Coupled Line Driving

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

luminance (Y) term. This usage accounts for the definition of luminance as stipulated by the International

Commission on Illumination (CIE). 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 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 R’G’B’ terms and,

thus, it is nonlinear. Chrominance (C) is derived from linear RGB, giving the difference between chroma (C’) and

nonlinear (gamma corrected) signals.

Copyright © 2011–2012, Texas Instruments Incorporated

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