MAX3964A/MAX3968
+3.0V to +5.5V, 125Mbps to 266Mbps
Limiting Amplifiers with Loss-of-Signal Detector
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Loss-of-Signal Comparator
The LOS comparator indicates when the input signal
power is below the programmed LOS threshold. To
ensure supply and temperature independence, VTH is
generated by a 1.2V bandgap reference. The op amp’s
external gain-setting resistors (R1 and R2) can be
chosen to set V
TH
between 1.2V and 2.4V. To ensure
chatter-free operation, the LOS comparator is designed
with approximately 5dB of hysteresis.
Squelch
The squelch function disables the data outputs by forc-
ing OUT- low and OUT+ high during a LOS condition.
This function ensures that when there is a loss of sig-
nal, the limiting amplifier (and all downstream devices)
does not respond to input noise or corrupt data.
Connect SQUELCH to GND or leave it unconnected to
disable squelch. Connect SQUELCH to V
CC
to enable
data squelching.
Applications Information
Program the LOS Threshold
Figure 2 provides information for selecting the LOS
threshold voltage (V
TH
). If R1 is 100kΩ and if the
responsivities of the photodiode and preamplifier are
known, then the value of R2 can be selected from Figure
2 to provide LOS assert at the desired input power.
Select Capacitors
A typical MAX3964A/MAX3968 implementation requires
four external capacitors (C
AZ
, C
FILTER
, and two input
coupling capacitors). For all applications up to
266Mbps, Maxim recommends the following:
C
AZ
= 1µF
C
FILTER
= 10nF
C
IN
= 4700pF
Wire Bonding
For high-current density and reliable operation, the
MAX3964A series uses gold metalization. Diepad size
is 4mils square with a 6mil pitch. Die thickness is
15mils.
