MAX3654 Maxim Integrated Products, MAX3654 Datasheet - Page 7

• Manufacturer Part Number: MAX3654
• Description: 47MHz to 870MHz Analog CATV Transimpedance Amplifier
• Manufacturer: Maxim Integrated Products

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The MAX3654 TIA is designed to operate with a low-
capacitance analog photodiode. Proper system design
includes considerations of lead configuration, pad, and
through-hole geometry, and PC board layer selection for
connections to the IC. The TIA is designed to operate
correctly when the total capacitance of the photodiode,
package, leads and PC board is between 1.0pF and
2.5pF.
The differential TIA RF output should be connected
(AC-coupled) to a balun transformer for normal single-
ended output.
For AGC operation, the optical average power can be
measured from the voltage drop across the lower bias
resistor, using high impedance to isolate the photodi-
ode as shown in the EV kit schematic. TIA gain is
inversely proportional to the voltage present at VAGC
from 0.175V to 1.4V. From 0 to 0.175V, the gain is con-
stant and maximum. The nominal gain is given by:
When connected as shown in the Typical Applications
Circuit, the MAX3654 will maintain the electrical output
constant (15dBmV/ch) for optical signals in the
-6dBm to +2dBm range.
The factory-assembled EV kit for the MAX3654 pro-
vides two versions: optical input and electrical input.
The optical input circuit includes photodiode bias cir-
cuitry, an op amp to adjust VAGC according to the DC
photodiode current (for AGC operation), an output
balun, and a 75Ω output connector. Through-hole pads
are provided to attach the triplexer analog photodiode
leads. Since photodiode capacitance and package
lead inductance affect the amount of uptilt, in configu-
rations where lead inductance is significantly lower
than the value shown in Figure 2, the uptilt may be
increased by providing discrete inductance on the PC
board. When a C
ZT dB
(
Evaluation Kit and PC Board Layout
Ω
)
( .
0 175
=
62
Applications Information
PD
dB
_______________________________________________________________________________________
V
Ω
≤
= 0.5pF (typ) photodiode is mount-
VAGC
+
20
×
Photodiode Parasitics
log
≤
1 4



.
VAGC mV
V
175
).
AGC Operation
mV
(
47MHz to 870MHz Analog CATV
RF Output
)



Transimpedance Amplifier
ed with 5mm (nominal) leads into through-hole vias as
in the EV kit configuration, a 4dB uptilt will normally be
achieved. It is important to configure the layout with
capacitance and inductance in the anode and cathode
connection as symmetric as possible.
The electrical input circuit is normally configured with a
50Ω input for use with conventional test and measure-
ment equipment. If desired, the MAX3654 input can
also be terminated with 75Ω as shown in the EV kit data
sheet. The 75Ω EV kit outputs should be connected to
50Ω test and measurement equipment using a mini-
mum loss pad.
For more information, see the Maxim website:
MAX3654 EV Kit data sheet—
http://www.maxim-ic.com/Fiber.cfm
Minimum Loss Pad—
http://www.maxim-ic.com/appnotes.cfm/appnote_number/972
TRANSISTOR COUNT: 3376
PROCESS: SiGe Bipolar
SUBSTRATE: SOI
*THE EXPOSED PAD MUST BE
CONNECTED TO GROUND.
TOP VIEW
TEST1
TEST2
GND
GND
13
14
15
16
12
1
4mm x 4mm
EP*
THIN QFN
MAX3654
11
2
Pin Configuration
Chip Information
10
3
9
4
8
7
6
5
GND
HYST
MUTE
VAGC
7