ADN2820

Rev. 0 | Page 8 of 12

APPLICATIONS

OPTICAL SENSITIVITY

)

1

(

2

)

/

1000

(

)

1

(

)

/

(

log

10

)

(

10

−

ρ

×

+

×

+

α

×

=

ER

W

mW

ER

Z

V

I

dBm

y

Sensitivit

T

S

RMS

where:

ρ = photodiode responsivity (A/W), 0.85 A/W typical

ADN2820

α = BER factor, α = 14.1 for 10–12 BER

ER = extinction ratio, 8 dB typical

Table 5. Optical Sensitivity

Optical Input Sensitivity (dBm)

2 kΩ

5 kΩ

Infinite

100 mV

–13.1

–15.7

–19.3

50 mV

–15.1

–17.1

–19.3

25 mV

–16.7

–18.1

–19.3

10 mV

–18.1

–18.8

–19.3

PA/CDR

Input

5 mV

–18.7

–19.0

–19.3

OPTICAL POWER MONITOR

Average optical power monitor (OPM) measurement is a

recommended diagnostic feature in module multisource

specification agreements (MSAs) such as the 300-pin 10 Gb

transponder (MSA300) and 10 Gb form factor pluggable

module (XFP) specifications.

The ADN2820 enables the simple calculation of OPM using the

POWMON output, which is linearly proportional to the average

input current. When monitoring the POWMON output,

connect to a high impedance input; typical POWMON output

impedance is 1 kΩ. To disable the POWMON feature, leave the

pad floating (not bonded).

Assuming linear diode responsivity ρ, average input current is

linearly proportional to average input power:

Ideally,

From a POWMON measurement, the average input power can

be estimated by calculating the optical power monitor (OPM):

OPM calculation from typical ADN2820 POWMON versus

–30

–25

–20

–15

–10

–5

0

–20

–15

–30

–25

–10

–5

0

AVERAGE INPUT POWER (dBm)

Figure 13. POWMON Transfer Function

–1.0

–0.6

–0.2

0.2

0.6

1.0

–20

–15

–30

–25

–10

–5

0

AVERAGE INPUT POWER (dBm)

Figure 14. POWMON Accuracy