THS3096PWPR datasheet(18/34 Pages) TI

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−

THS3092

20 V

−

1:1

THS3092

330 pF

22 pF

10 V

200 W

100 W

14.5 dBm

Line Power

200 W

604 W

4.99 kW

0.01 mF

191 W

604 W

1.21 kW

24.9 W

6.8 mF

0.01 mF

24.9 W

*Hybrid Connection Not

Shown For Simplicity

DAC

VIN+

DAC

VIN−

1.21 kW

Video Distribution

−

THS3092

26 V

−

1:1

THS3092

To RX

Hybrid

330 pF

22 pF

13 V

0.01 mF

6.8 mF

4.99 kW

200 W

DAC

VIN+

22 pF

133 W

604 W

0.015 mF

200 W

4.99 kW

49.9 W

14.5 dBm

Line Power

100 W

DAC

VIN−

THS3092

THS3096

SLOS428A – DECEMBER 2003 – REVISED FEBRUARY 2004

Figure 55 shows a traditional hybrid connection

One of the concerns about any DSL line driver is the

approach for achieving the 14.5-dBm line power

power dissipation. One of the most common ways to

utilizing a 1:1 transformer. Looking at the input to the

reduce power is by using active termination, aka

amplifiers shows a low-pass filter consisting of two

synthesized impedance. Refer to TI Application Note

separate capacitors to ground. There is an argument

SLOA100 for more information on active termination.

that since the signal coming out of the DAC is

The drawback to active termination is the received

fully-differential then a single capacitor (10 pF in this

signal is reduced by the same synthesis factor

case) is perfectly acceptable. The problem with this

utilized in the system. Due to the very high attenu-

idea is that many DACs have common-mode energy

ation of the line at up to 12 MHz, the receive signal

due to images around the sampling frequency which

can be severely diminished. Thus, the use of active

must be filtered before reaching the amplifier. An

termination should be kept to modest levels at best.

amplifier simply amplifies its input–including the

Figure 56 shows an example of utilizing a simple

DAC’s images at high frequencies–and pass it

active termination scheme with a synthesis factor of 2

through to the transformer and ultimately to the line,

to achieve the same line power, but with a reduced

possibly causing the system to fail EMC compliance.

power supply voltage that ultimately saves power in

A single capacitor does not remove these com-

the system.

mon-mode images, it only removes the differential

signal images. However, two separate filter capaci-

tors filter both the common-mode signals and the

differential-mode signals. Be sure to place the ground

connection point of the capacitors next to each other,

and then tie a single ground point at the middle of this

trace.

Figure 56.

The wide bandwidth, high slew rate, and high output

drive current of the THS3092/6 matches the demands

for video distribution for delivering video signals down

Figure 55.

multiple cables. To ensure high signal quality with

minimal degradation of performance, a 0.1-dB gain

flatness should be at least 7x the passband fre-

Additionally, level shifting must be done to center the

quency to minimize group delay variations from the

common-mode voltage appearing at the amplifier’s

amplifier. A high slew rate minimizes distortion of the

noninverting input to optimally the midpoint of the

video signal, and supports component video and

power

supply.

side

benefit

the

RGB video signals that require fast transition times

ac-coupling/level shifter, a simple high pass filter is

and fast settling times for high signal quality.

formed. This is generally a good idea for VDSL

systems where the transmit band is typically above 1

MHz, but can be as low as 25 kHz.

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