MAX3964A Datasheet, PDF (7/12 Pages) Maxim Integrated Products – +3.0V to +5.5V, 125Mbps to 266Mbps Limiting Amplifiers with Loss-of-Signal Detector

+3.0V to +5.5V, 125Mbps to 266Mbps
Limiting Amplifiers with Loss-of-Signal Detector
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 30mV_P-P.
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/MAX3965/MAX3968 implementa-
tion 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 = 27nF
C_FILTER = 10nF
C_IN = 10nF
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.
120
200kV/W
100
80
100kV/W
60
30kV/W
20kV/W
40
15kV/W
20
10kV/W
0
-40 -38 -36 -34 -32 -30 -28 -26
OPTICAL INPUT POWER AT LOS ASSERT (dBm)
Selector Guide
PART
MAX3964A*
DATA RATE (Mbps)
125 to 155
LOS OUTPUTS
PECL
MAX3965
MAX3968
125 to 155
125 to 266
TTL
PECL
*The MAX3964A is functionally equivalent to MAX3964, but offers
slightly improved ESD tolerance. The MAX3969 is a recommend-
ed upgrade for the MAX3964, MAX3964A, MAX3965, and
MAX3968.
Figure 2. LOS Assert Programming Resistor vs. LOS Assert
Power (for Various PIN-TIA Gains )
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