SN10501DBVR datasheet(12/23 Pages) TI

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SN10501

SN10502

SN10503

SLOS408A − MARCH 2003 − REVISED DECEMBER 2003

www.ti.com

Differential gain and phase measure the change in overall

small-signal gain and phase for the color subcarrier

frequency (3.58 MHz in NTSC systems) vs changes in the

large-signal output level (which represents luminance

information in a composite video signal). The SN1050x,

with the typical 150-

Ω load of a single matched video

cable, shows less than 0.007% / 0.007

° differential

gain/phase errors over the standard luminance range for

positive

video

(negative

sync)

signal.

Similar

performance is observed for negative video signals. In

practice, similar performance is achieved even with three

video loads as shown in Figure 37 due to the linear

high-frequency output impedance of the SN1050x.

−

Video In

µF

0.1

µF

VS−

Ω

µF

0.1

µF

1.43 k

Ω

1.43 k

Ω

VS+

Ω

Figure 37. Video Distribution

The above circuit is suitable for driving video cables,

provided that the length does not exceed a few feet. If

longer cables are driven, the gain of the SN1050x can be

increased to accommodate cable drops.

Configuring the SN1050x for single supply video

applications is easily done. But, attention must be made to

the bias voltages at the input and output to ensure the

system works as desired. Unlike some video amplifiers,

the input common-mode voltage range of the SN1050x

amplifiers do not include the negative power supply, but

rather it is about 1-V from each power supply. For split

supply configurations, this is very beneficial. But for

single-supply systems, there are some design constraints

that must be adhered to.

Figure 38 shows a single supply video configuration

illustrating the dc bias voltages acceptable for the

SN1050x. The lower end of the input common-mode range

is specified as 1 V. While the upper end is limited to 4 V with

the 5-V supply shown, the output range and gain of 2 limits

the highest acceptable input voltage to 4.5 V / 2 = 2.25 V.

The 4.5-V output is what is typically expected with a 150-

Ω

load. It is easily seen that the input voltage range and/or

the output voltage range will be the limiting factor in the

total system and both specifications must be taken into

account when designing a system.

−

Ω

1.24 k

Ω

1.24 k

Ω

5 V

Input Range

= 1 V to 2.25 V

Output Range

= 2 V to 4.5 V

VO Range

= 1 V to 2.25 V

Figure 38. DC-Coupled Single-Supply Video

Amplifier

In most systems, this may be acceptable because most

receivers are ac-coupled and set the blank level to the

desired system value, typically 0 V (0-IRE). But, to ensure

full compatibility with any system, it is often desirable to

place an ac-coupling capacitor on the output as shown in

Figure 39. This eliminates the dc-bias voltage appearing

at the amplifier output. To minimize field tilt, the size of this

capacitor is typically 470

µF, although values as small as

220

µF have been utilized with acceptable results.

−

Ω

1.24 k

Ω

1.24 k

Ω

5 V

Input Range

= 1 V to 2.25 V

Output Range

= 2 V to 4.5 V

VO Range

= 0 V to 1.25V

470

µF

Figure 39. AC-Coupled Output Single-Supply

Video Amplifier

In some systems, the physical size and sometimes cost of

a 470-

µF capacitor can be prohibitive. One way to

circumvent this issue is to utilize two smaller capacitors in

a feedback configuration as shown in Figure 40. This is

commonly known as SAG correction. This circuit

increases the gain of the amplifier up to 3 V/V at low

frequencies to counteract the increased impedance of the

capacitor placed at the amplifier output. One issue that

must be resolved is the gain at low frequencies is typically

limited by the power-supply voltage and the output swing

of the amplifier. Therefore, it is possible to saturate the

amplifier at these low frequencies if full analysis is not done

on this system which includes both input and output

requirements.

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