SN10501DBVT datasheet(12/32 Pages) NSC

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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

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

µF

1.24

Ω

µF

−

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

SN10501

SN10502

SN10503

SLOS408B – MARCH 2003 – REVISED JANUARY 2009 .................................................................................................................................................. www.ti.com

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. This 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 compensate for cable

loss.

Configuring the SN1050x for single-supply video

applications is easily done, but attention must be

given to input and output bias voltages to ensure

Figure 39. AC-Coupled Output Single-Supply

Video Amplifier

proper

system

operation.

Unlike

some

video

amplifiers, the SN1050x input common-mode voltage

range does not include the negative power supply,

In some systems, the physical size and/or cost of a

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

470-

µF capacitor can be prohibitive. One way to

split supply configurations, this is very beneficial. For

circumvent this issue is to use two smaller capacitors

single-supply

systems,

there

are

some

design

in a feedback configuration as shown in Figure 40.

constraints that must be observed.

This is commonly known as SAG correction. This

circuit increases the gain of the amplifier up to 3 V/V

Figure 38 shows a single-supply video configuration

at low frequencies to counteract the increased

illustrating the dc bias voltages acceptable for the

impedance of the capacitor placed at the amplifier

SN1050x. The lower end of the input common-mode

output. One issue that must be resolved is that the

range is specified as 1 V. The upper end is limited to

gain at low frequencies is typically limited by the

4 V with the 5-V supply shown, but the output range

power-supply voltage and the output swing of the

and gain of 2 limit the highest acceptable input

amplifier. Therefore, it is possible to saturate the

voltage to 4.5 V / 2 = 2.25 V. The 4.5-V output is

amplifier at these low frequencies if full analysis is not

what is typically expected with a 150-

Ω load. It is

done on this system which includes both input and

easily seen that the input and output voltage ranges

output requirements.

are

limiting

factors

the

total

system.

Both

specifications must be taken into account when

designing a system.

Figure 40. AC-Coupled SAG Corrected Output

Single-Supply Video Amplifier

Figure 38. DC-Coupled Single-Supply Video

Amplifier

Many times the output of the video encoder or DAC

does not have the capability to output the 1-V to

2.25-V range, but rather a 0-V to 1.25-V range. In this

In most systems, this may be acceptable because

instance, the signal must be ac-coupled to the

most receivers are ac-coupled and set the black level

amplifier input as shown in Figure 41. Note that it

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

does not matter what the voltage output of the DAC

But, to ensure full compatibility with any system, it is

is, but rather the voltage swing should be kept less

often desirable to place an ac coupling capacitor on

than 1.25 VPP.

the output as shown in Figure 39. This removes 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 used with acceptable results.

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