MAX3658AETA+T Maxim Integrated Products, MAX3658AETA+T Datasheet - Page 7

• Manufacturer Part Number: MAX3658AETA+T
• Description: IC AMP TRANSIMPEDANCE 8-TDFN
• Manufacturer: Maxim Integrated Products
• Type: Transimpedance Amplifierr

Specifications of MAX3658AETA+T

• Applications: Optical Networks
• Mounting Type: Surface Mount
• Package / Case: 8-TDFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Figure 2. DC Cancellation Effect on Input
The output buffer is designed to drive a 150Ω differen-
tial load between OUT+ and OUT-. For optimum supply
noise rejection, the MAX3658 should be terminated with
a differential load. The MAX3658 single-ended outputs
do not drive a DC-coupled grounded load. The outputs
should be AC-coupled or terminated to V
ended output is required, both the used and the unused
outputs should be terminated in a similar manner (see
the Interface Schematics section).
The DC cancellation circuit uses low-frequency feed-
back to remove the DC component of the input signal
(Figure 2). This feature centers the input signal within
the transimpedance amplifier’s linear range, thereby
reducing pulse-width distortion.
The DC cancellation circuit is internally compensated
and does not require external capacitors. This circuit
minimizes pulse-width distortion for data sequences
that exhibit a 50% mark density. A mark density signifi-
cantly different from 50% causes the MAX3658 to gen-
erate pulse-width distortion. Grounding the FILT pin
disables the DC cancellation circuit. For normal opera-
tion, the DC cancellation circuit must be enabled.
The DC cancellation current is drawn from the input and
creates noise. For low-level signals with little or no DC
component, the added noise is insignificant. However,
amplifier noise increases for signals with significant DC
component (see the Typical Operating Characteristics ).
The MAX3658 includes an average photocurrent moni-
tor. The current sourced from MON to ground is approxi-
mately equal to the DC current at IN.
AMPLITUDE
INPUT AFTER DC CANCELLATION
_______________________________________________________________________________________
INPUT FROM PHOTODIODE
DC Cancellation Circuit
Photocurrent Monitor
Output Buffer
622Mbps, Low-Noise, High-Gain
CC
. If a single-
TIME
Transimpedance Preamplifier
Noise performance and bandwidth are adversely affected
by capacitance on the TIA input node. Select a low-
capacitance photodiode to minimize the total input capac-
itance on this pin. The MAX3658 is optimized for 0.5pF of
capacitance on the input. Assembling the MAX3658 in die
form using chip and wire technology provides the lowest
capacitance input and the best possible performance.
Supply voltage noise at the cathode of the photodiode
produces a current i = C
receiver sensitivity (C
tance). The filter resistor of the MAX3658 combined
with an external capacitor, can be used to reduce the
effect of supply noise on performance (see the Typical
Operating Circuit ). Current generated by supply noise
voltage is divided between C
good optical sensitivity select C
Sensitive optical receivers require wide-band power-
supply decoupling. Power-supply bypassing should
provide low impedance between V
frequencies between 10kHz and 700MHz. Isolate the
MAX3658 from noise sources with LC supply filters and
shielding. Place a supply filter (C
MAX3658 as possible.
If photocurrent monitoring is desired, connect a resistor
between MON and ground to monitor the average pho-
tocurrent. Select R
where I
observed. An ammeter can also monitor the current out
of the MON pin.
A receiver built with the MAX3658 will have a bandpass
frequency response. The low-frequency cutoff due to
the coupling capacitors and load resistors is:
LFC
MONMAX
TERM
R
is the largest average input current
=
MON
MON
Select Coupling Capacitors
2π
PD
as large as possible:
×
=
PD
Design Procedure
is the photodiode capaci-
R
I
MONMAX
LOAD
FILT
dv/dt, which reduces the
Select Supply Filter
2 2
FILT
.
Select Photodiode
V
VCC2
and C
1
×
≈ 400pF.
CC
C
) as close to the
Select R
Select C
and ground for
COUPLE
PD
. To obtain a
MON
FILT
7