SN10501DBVR datasheet(11/32 Pages) NSC

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Video Drive Circuits

SINGLE SUPPLY OPERATION

−

Video In

µF

0.1

µF

VS−

Ω

µF

0.1

µF

1.43 k

Ω

1.43 k

Ω

VS+

49.9

Ω

Ω Source

+VS

1.3 k

Ω

1.3 k

Ω

+VS

1.3 k

Ω

Ω Source

1.3 k

Ω

52.3

Ω

499

Ω

499

Ω

+VS

−

Video In

µF

0.1

µF

VS−

Ω

µF

0.1

µF

1.43 k

Ω

1.43 k

Ω

VS+

Ω

SN10501

SN10502

SN10503

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

as the noninverting circuit in Figure 33. However, the

amplifier output now sees the 100-

Ω feedback

Most video-distribution systems are designed with

resistor in parallel with the external load. To eliminate

75-

Ω series resistors to drive a matched 75-Ω cable.

this excessive loading, increase both Rg and Rf,

In order to deliver a net gain of 1 to the 75-

Ω

values, as shown in Figure 34, and then provide the

matched load, the amplifier is typically set up for a

input-matching impedance with a third resistor (RM) to

voltage gain of 2, compensating for the 6-dB

ground. The total input impedance becomes the

attenuation of the voltage divider formed by the series

parallel combination of Rg and RM.

and shunt 75-

Ω resistors at either end of the cable.

The last major consideration to discuss in inverting

The

circuit

shown

Figure

meets

this

amplifier

design

setting

the

bias-current

requirement.

The

SN1050x

gain

flatness

and

cancellation resistor on the noninverting input. If the

differential

gain/phase

performance

provide

resistance is set equal to the total dc resistance

exceptional results in video distribution applications.

looking out of the inverting terminal, the output dc

error, due to the input bias currents, is reduced to the

input-offset current multiplied by Rf in Figure 34. The

dc source impedance looking out of the inverting

terminal is 1.3 k

Ω || (1.3 kΩ + 25.6 Ω) = 649 Ω. To

reduce the additional high-frequency noise introduced

by the resistor

the

noninverting

input,

and

power-supply feedback, RT is bypassed with a

capacitor to ground.

The SN1050x family is designed to operate from a

single 3-V to 15-V power supply. When operating

from a single power supply, care must be taken to

ensure that the input signal and amplifier are biased

appropriately to allow for the maximum output voltage

Figure 36. Cable Drive Application

swing. The circuits shown in Figure 35 demonstrate

methods to configure an amplifier for single-supply

Differential gain and phase measure the change in

operation.

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 a positive

video (negative sync) signal.

Figure 35. DC-Coupled Single Supply Operation

Figure 37. Video Distribution

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