9

®

AFE1103

DISCUSSION OF

SPECIFICATIONS

UNCANCELLED ECHO

The key measure of transceiver performance is uncancelled

echo. This measurement is made as shown in the diagram of

Figure 4. The AFE is connected to an output circuit includ-

ing a typical 1:2 line transformer. The line is simulated by a

135

Ω resistor. Symbol sequences are generated by the tester

and applied both to the AFE and to the input of an adaptive

filter. The output of the adaptive filter is subtracted from the

AFE output to form the uncancelled echo signal. Once the

filter taps have converged, the RMS value of the uncancelled

echo is calculated. Since there is no far-end signal source or

additive line noise, the uncancelled echo contains only noise

and linearity errors generated in the transmitter and receiver.

The data sheet value for uncancelled echo is the ratio of the

RMS uncancelled echo (referred to the receiver input through

the receiver gain) to the nominal transmitted signal (13.5dBm

into 135

Ω, or 1.74Vrms). This echo value is measured under

a variety of conditions: with loopback enabled (line input

disconnected); with loopback disabled under all receiver

POWER DISSIPATION

Approximately 75% of the power dissipation in the AFE1103

is in the analog circuitry, and this component does not

change with clock frequency. However, the power dissipa-

tion in the digital circuitry does decrease with lower clock

frequency. In addition, the power dissipation in the digital

section is decreased when operating from a smaller supply

remain in the range 4.75V to 5.25V.)

The power dissipation listed in the specifications section

applies under these normal operating conditions: 5V Analog

Power Supply; 3.3V Digital Power Supply; standard 13.5dBm

delivered to the line; and a pseudo-random equiprobable

sequence of HDSL output pulses. The power dissipation

specifications includes all power dissipated in the AFE1103,

it does not include power dissipated in the external load.

The external power is 16.5dBm, 13.5dBm to the line and

13.5dBm to the impedance matching resistors. The external

load power of 16.5dBm is 45mW. The typical power dissi-

pation in the AFE1103 under various conditions is shown in

Table I.

FIGURE 4. Uncancelled Echo Test Diagram.

TYPICAL POWER

BIT RATE

DISSIPATION

PER AFE1103

DVDD

IN THE AFE1103

(Symbols/sec)

(V)

(mW)

584 (E1)

3.3

250

584 (E1)

5

300

392 (T1)

3.3

240

392 (T1)

5

270

146 (E1/4)

3.3

230

146 (E1/4)

5

245

TABLE I. Typical Power Dissipation.

rxHYB

N

AFE1103

rxLINE

P

rxLINE

N

REF

N

rxD13 - rxD0

rxHYB

P

txLINE

N

txLINE

P

txDAT

P

100pF

0.01µF

576

Ω

1.54k

Ω

13

Ω

13

Ω

5.6

Ω

1:2

5.6

Ω

0.047µF

150

Ω

576

Ω

0.047µF

2k

Ω

2k

Ω

100pF

750

Ω

Transmit

Data

Uncanceled

Echo

0.1µF

750

Ω

0.1µF

2k

Ω

2k

Ω

135

Ω

S

1