The equation for total DC error is:

[Equation 3]

The total output-referred noise voltage is:

[Equation 4]

The MAX9480/MAX9481/MAX9482 have very low noise

√Hz (typ). The current noise at

√Hz (typ), and the

√Hz (typ).

An example of the DC error calculations, using the

MAX9480 data and the Typical Operating Circuit where

the following, using equation 3:

Calculating total preamp output noise using equation 4

yields 16.6nV/

√Hz, which then contributes 50nV/√Hz at

the driver output. The driver noise contributes an addi-

tional 35mV/

√Hz, to the overall output noise.

Driving Capacitive Loads

The MAX9480/MAX9481/MAX9482 receive amplifiers

are optimized for AC performance. They are not

designed to drive highly capacitive loads. Reactive

loads decrease phase margin and can produce exces-

sive ringing and oscillation.

Output-Impedance Synthesis

To help meet the contradictory requirements of high

output power and low-power use, the active termination

circuit shown in Figure 5 is used. This circuit is

designed to present a line termination of 8

Ω. R1 is a

physical 1.6

Ω resistor voltage feedback from the out-

board end of R1 to the noninverting input of the amplifi-

er, introduces positive feedback, which increases the

effective output-impedance value from 1.6

Ω to 8Ω.

Hence, the impedance looking into the port matches

the line impedance reflected through the transformer.

Assuming an ideal amplifier, the following equation

expresses the output impedance:

Substituting the values of the resistors shown in Figure

Ω.

The output equivalent circuit for the line driver is shown

in Figure 5.

Z

R

R

R

R

RR

Equation

−+









+

[]

1

7

8

10

910

11

5

V

x

×

+









++





































−−

1 0

10

50

2 6 10

1000 1000

1000 1000

0 002

1

1000

1000

66

..

.

e

R

R

iRs

i

R

R

e

n OUT

F

G

nn

F

G

n

()

||

(

)

=+







+−

1

22

2

VI

R

I

R

R

V

R

R

OUT

B

S

B

F

G

OS

F

G

=









+−

()(

||

)

1

Low-Power, Low-Distortion, Central-Office

ADSL Drivers and Integrated Drivers/Receivers

10

______________________________________________________________________________________

R7

800

Ω

R8

667

Ω

R1

1.6

Ω

R9

945

Ω

R10

540

Ω

Figure 4. Active Line Termination Scheme, Single Side

MAX9480

MAX9481

MAX9482

Figure 3. Input Offset Voltage and Current