AD8392

Rev. 0 | Page 14 of 16

Additional definitions for calculating resistor values include:

Voltage at the amplifier outputs

k

Matching resistance reduction factor

β

Negative feedback factor

α

Positive feedback factor

Note: R1 must be calculated before

β and α.

()

N

k

V

V

LINE

OA

+

=

1

L

m

R

R

k

2

=

IN

LINE

V

V

N

V

A =

R2

R1

R1

2

β

+

=

(

)

k

−

= 1

β

α

With the above known quantities and definitions, the remaining

resistors can readily be calculated.

P

OA

P

V

V

R

V

R1

−

=

2

2

()

IN

P

IN

IN

V

2

V

V

R

R4

−

=

(

)

()

R2

R1

R

R

R2

R

R1

R

R1

R

R1

R4

A

R3

L

L

L

L

m

V

2

α

2α

α

2

+

−

−

+

=

()

R4

R3

R4

R4

R3

+

−

=

α

α

After building the circuit with the closest 1% resistor values,

the actual gain, input resistance, and output resistance can be

verified with the following equations.

()

()

R3

R4

R

R4

R3

R4

k

N

GAIN

BIAS

LINE

to

−

⎟

⎠

⎞

⎜

⎝

⎛

+

+

+

=

1

1

β

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

+

−

=

L

L

m

V

IN

R

R4

R

R

A

R4

R

2

β

1

2

()

⎟

⎟

⎟

⎟

⎠

⎞

⎜

⎜

⎜

⎜

⎝

⎛

+

+

+

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

+

−

=

BIAS

BIAS

BIAS

BIAS

m

OUT

R

R4

R

R4

R3

R2

R1

R

R4

R1

R

R4

N

R

R

2

1

2

2

MULTITONE POWER RATIO

The DMT signal used in ADSL/ADSL2+ systems carries data in

discrete tones or bins, which appear in the frequency domain in

evenly spaced 4.3125 kHz intervals. In applications using this

type of waveform, multitone power ratio (MTPR) is a com-

monly used measure of linearity. Generally, there are two types

of MTPR that designers are typically concerned with: in-band

and out-of-band MTPR. In-band MTPR is defined as the

measured difference from the peak of one tone that is loaded

with data to the peak of an adjacent tone that is intentionally

left empty. Out-of-band MTPR is more loosely defined as the

spurious emissions that occur in the receive band located

between 25.875 kHz and the first downstream tone at 138 kHz.

Figure 38 and Figure 39 show the AD8392 in-band MTPR for a

5.5 crest factor waveform for empty bins in the ADSL and

extended ADSL2+ bandwidths. Figure 40 shows the AD8392

out-of-band MTPR for the same waveform.

CENTER 647kHz

–120

–110

–100

–90

–80

–70

–60

–50

–40

–30

–20

SPAN 10kHz

1kHz/

72.2dB

Figure 38. In-Band MTPR at 647 kHz

CENTER 1.75MHz

–120

–110

–100

–90

–80

–70

–60

–50

–40

–30

–20

SPAN 10kHz

1kHz/

64.4dB

Figure 39. In-Band MTPR at 1.751 MHz