THS6204IPWPR datasheet(25/43 Pages) TI

25 / 43 page

DUAL-SUPPLY VDSL DOWNSTREAM

LINE

(3)

LINE DRIVER HEADROOM MODEL

P =10

log

(1mW)

´ L

RMS

(4)

RMS

(1mW)

(5)

V =CrestFactor

=CF

RMS

(6)

RMS

(7)

1.33kW

2kW

0.1 F

9.1W

100W

LINE

AFE

Max

Assumed

2kW

20W

2kW

1/4

THS6204

1/4

THS6204

+12V

-12V

1:1.1

I =159mA

9.1W

2.7kW

LPP

(1mW)

(8)

=1+

´ F

(2)

±I =

´ LPP

(9)

THS6204

www.ti.com ................................................................................................................................................... SBOS416C – OCTOBER 2007 – REVISED APRIL 2009

the phone line, and also provide a means of detecting

the received signal for the receiver. The value of

Figure 82 shows an example of a dual-supply VDSL

these resistors (RM) is a function of the line

downstream driver. Both channels of the THS6204

impedance and the transformer turns ratio (n), given

are configured as a differential gain stage to provide

by the following equation:

signal drive to the primary winding of the transformer

(here, a step-up transformer with a turns ratio of

1:1.1). The main advantage of this configuration is

the cancellation of all even harmonic distortion

products. Another important advantage for VDSL is

that each amplifier needs only to swing half of the

total output required driving the load.

The first step in a transformer-coupled, twisted-pair

driver design is to compute the peak-to-peak output

voltage from the target specifications. This is done

using the following equations:

with PL power at the load, VRMS voltage at the load,

and RL load impedance; this gives the following:

with VP peak voltage at the load and CF Crest Factor.

with VLPP: peak-to-peak voltage at the load.

Consolidating Equation 4 through Equation 7 allows

expressing the required peak-to-peak voltage at the

load as a function of the crest factor, the load

Figure 82. Dual-Supply VDSL Downstream Driver

impedance, and the power at the load. Thus,

The analog front end (AFE) signal is ac-coupled to

the driver, and the noninverting input of each

amplifier is biased to the mid-supply voltage (ground

in this case). In addition to providing the proper

This VLPP is usually computed for a nominal line

biasing to the amplifier, this approach also provides a

impedance and may be taken as a fixed design

high-pass filtering with a corner frequency, set here at

target.

5kHz. As the signal bandwidth starts at 26kHz, this

The next step in the design is to compute the

high-pass filter does not generate any problem and

individual amplifier output voltage and currents as a

has the advantage of filtering out unwanted lower

function of VPP on the line and transformer turns ratio.

frequencies.

As this turns ratio changes, the minimum allowed

The input signal is amplified with a gain set by the

supply voltage changes along with it. The peak

following equation:

current in the amplifier output is given by:

With RF = 2kΩ and RG = 1.33kΩ, the gain for this

differential amplifier is RP = 2.1kΩ. This gain boosts

the AFE signal, assumed to be a maximum of 2VPP,

to a maximum of 3VPP.

The two back-termination resistors (9.1

Ω each)

added at each terminal of the transformer make the

impedance of the modem match the impedance of

Submit Documentation Feedback

Product Folder Link(s): THS6204

THS6204IPWPR Datasheet(PDF) 25 Page - Texas Instruments

THS6204IPWPR Datasheet(HTML) 25 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Datasheet Download

Link URL