For LOS assert at -35dBm, select R1 = 100k

Ω and R2 =

22k

Ω, which programs the LOS assert at input ≅ 3mV.

With this selection, LOS assert time will typically be less

than 85µs.

Fibre Channel Component Selection

In Fibre Channel applications, the desired LOS assert

time is typically 25µs maximum, and data-dependent

jitter is reduced by 8B10B coding techniques. The fol-

lowing are recommended in a Fibre Channel system

where preamp gain is 2000V/W, LOS assert is set for

-24dBm (13mV MAX3761/MAX3762 input), and the

maximum input to the MAX3761/MAX3762 is 1Vp-p:

R1 = 100k

Ω, R2 = 50kΩ (to set LOS assert at -24dBm)

PECL Terminations

The standard PECL termination (50

recommended for best performance and output char-

acteristics. The data outputs operate at high speed,

and should always drive transmission lines with

50

Ω to 75Ω terminations. Balanced termination is rec-

ommended for all outputs.

Figure 5 shows an alternative method for terminating

the data outputs. The technique provides approximate-

ly 8mA DC bias current, with a 50

Ω AC load, for the

output termination. This technique is useful for viewing

the output on an oscilloscope or changing the PECL

reference voltage.

The MAX3762’s PECL LOS outputs are relatively slow

and do not need 50

Ω terminations (although they are

capable of driving them). To reduce power, the

MAX3762’s LOS outputs can be terminated with 500

Ω.

Figure 6 shows a typical operating circuit for the

MAX3762.

Wire Bonding

For high current density and reliable operation, the

MAX3761/MAX3762 use gold metalization. Make con-

nections to the dice with gold wire only, and use ball-

bonding

techniques

(wedge

bonding

is

not

recommended). Die-pad size is 4 mils square, with a

6 mil pitch. Die thickness is 12 mils (0.3mm).

Layout Techniques

The MAX3761/MAX3762 are high-frequency, high-

bandwidth circuits. To ensure stability, use good high-

frequency layout techniques. Filter voltage supplies,

and keep ground connections short. Use multiple vias

where possible. Use controlled-impedance transmis-

sion lines to connect the MAX3761/MAX3762 data out-

puts to other circuits.

Low-Power, 622Mbps Limiting Amplifiers

with Chatter-Free Power Detect for LANs

10

______________________________________________________________________________________

470

Ω

DRIVING 50

Ω TO GROUND

470

Ω

50

Ω

50

Ω

OUT+

OUT-

MAX3761

Figure 5. Alternative PECL Termination