MAX3968 Maxim Integrated Products, MAX3968 Datasheet - Page 7

• Manufacturer Part Number: MAX3968
• Description: (MAX3964 - MAX3968) 125Mbps to 266Mbps Limiting Amplifiers
• Manufacturer: Maxim Integrated Products

sensitivity. The offset-correction circuitry is less sensi-
tive to variations of input duty cycle (for example, the
40% to 60% duty cycle encountered in 4B/5B coding)
when the input is less than 30mVp-p.
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
chatter-free operation, the LOS comparator is designed
with approximately 5dB of hysteresis.
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
data squelching.
Figure 2. LOS Assert Programming Resistor vs. LOS Assert
Power (for various PIN-TIA gains )
Limiting Amplifiers with Loss-of-Signal Detector
120
100
80
60
40
20
0
-40
OPTICAL INPUT POWER AT LOS ASSERT (dBm)
-38
TH
_______________________________________________________________________________________
30kV/W
between 1.2V and 2.4V. To ensure
-36
Loss-of-Signal Comparator
200kV/W
-34
10kV/W
100kV/W
+3.0V to +5.5V, 125Mbps to 266Mbps
-32
15kV/W
-30
20kV/W
-28
CC
Squelch
to enable
-26
Figure 2 provides information for selecting the LOS
threshold voltage (V
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.
A typical MAX3964/MAX3965/MAX3968 implementation
requires four external capacitors (C
two input coupling capacitors). For all applications up
to 266Mbps, Maxim recommends the following:
For high-current density and reliable operation, the
MAX3964 series uses gold metalization. Diepad size is
4mils square with a 6mil pitch. Die thickness is 15mils.
MAX3964
MAX3965
MAX3968
PART
Applications Information
DATA RATE (Mbps)
Program the LOS Threshold
C
FILTER
C
C
TH
AZ
125 to 155
125 to 155
125 to 266
IN
). If R1 is 100kΩ and if the
= 10nF
= 27nF
= 10nF
Selector Guide
Select Capacitors
AZ
Wire Bonding
, C
LOS OUTPUTS
FILTER
PECL
PECL
TTL
, and
7