Applications Information

Optical Power Relations

Many of the MAX3793 specifications relate to the input

signal amplitude. When working with optical receivers,

the input is sometimes expressed in terms of average

optical power and extinction ratio. Figure 5 and Table 1

show relations that are helpful for converting optical

power to input signal when designing with the

MAX3793.

Optical Sensitivity Calculation

MAX3793 generally determines the receiver sensitivity.

To obtain a system bit-error rate (BER) of 1E-12, the

signal-to-noise ratio must always exceed 14:1. The

input sensitivity, expressed in average power, can be

estimated as:

is the RMS noise current in amps.

Input Optical Overload

Overload is the largest input that the MAX3793 accepts

while meeting DJ specifications. Optical overload can

be estimated in terms of average power with the follow-

ing equation:

Optical Linear Range

The MAX3793 has high gain, which limits the output

operates in a linear range for inputs not exceeding:

Linear Range

Ar

r

dBm

e

e

log

=

µ×

+

()

××

−

()

×













10

50

1

21

1000

ρ

Overload

I

dBm

OL

log

=

×

×













10

2

1000

ρ

Sensitivity

Ir

r

dBm

Ne

e

log

.

)

=

×+

()

××

−

()

×













10

14 1

1

21

1000

ρ

1Gbps to 4.25Gbps Multirate Transimpedance

Amplifier with Photocurrent Monitor

_______________________________________________________________________________________

9

PO

PI

TIME

Figure 5. Optical Power Relations

PARAMETER

SYMBOL

RELATION

Average power

Extinction ratio

Optical power of a 1

P1

Optical power of a 0

P0

Optical modulation amplitude

Table 1. Optical Power Relations*

r

r

e

e

12

1

=

+

PP

P

P

IN

AVG

r

r

e

e

==

−

−

+

10

2

*Assuming a 50% average mark density.