19-1601; Rev 2; 11/05
622Mbps, Ultra-Low-Power, 3.3V
Transimpedance Preamplifier for SDH/SONET
________________General Description
The MAX3665 low-power transimpedance preamplifier
for 622Mbps SDH/SONET applications consumes only
70mW at V
CC
= 3.3V. Operating from a single +3.3V or
+5.0V supply, it converts a small photodiode current to a
measurable differential voltage. A DC cancellation circuit
provides a true differential output swing over a wide
range of input current levels, thus reducing pulse-width
distortion. The differential outputs are back-terminated
with 50Ω per side.
The overall transimpedance gain is nominally 8kΩ. For
input signal levels beyond approximately 50µAp-p, the
amplifier will limit the output swing to 250mV. The
MAX3665’s low 55nA input noise provides a typical
sensitivity of -33.2dBm in 1300nm, 622Mbps receivers.
The MAX3665 is designed to be used in conjunction
with the MAX3676 clock recovery and data retiming IC
with limiting amplifier. Together they form a complete
3.3V or 5.0V 622Mbps SDH/SONET receiver.
In die form, the MAX3665 is designed to fit on a header
with a PIN diode. It includes a filter connection that pro-
vides positive bias for the photodiode through a 1.5kΩ
resistor to V
CC
. The device is available in an 8-pin
µMAX
®
package.
IT
TION K
VALUA
E
BLE
AVAILA
____________________________Features
♦
+3.3V or +5.0V Single-Supply Operation
♦
55nA
RMS
Input-Referred Noise
♦
70mW Power Consumption at V
CC
= 3.3V
♦
8kΩ Gain
♦
450µA Peak Input Current
♦
260ps (max) Deterministic Jitter
♦
Differential Output Drives 100Ω Load
♦
470MHz Bandwidth
MAX3665
_______________Ordering Information
PART
MAX3665EUA
MAX3665E/D
TEMP RANGE
-40°C to +85°C
(see Note)
PIN-PACKAGE
8 µMAX
Dice
Note:
Dice are designed to operate over a -40°C to +140°C
junction temperature (T
j
) range, but are tested and guaranteed
at T
A
= +25°C.
________________________Applications
SDH/SONET Receivers
PIN Photodiode Preamplifiers and Receivers
Regenerators for SDH/SONET
Pin Configuration appears at end of data sheet.
µMAX is a registered trademark of Maxim Integrated Products, Inc.
__________________________________________________Typical Application Circuit
3.3V
0.01µF
R
FILT
1.5kΩ
FILT
C
FILT
V
CC
MAX3665
3.3V
OUT+
IN
50Ω
0.1µF
CLOCK
AND
DATA
RECOVERY
CLK
50Ω
OUT-
0.1µF
LIMITING
AMP
DATA
MAX3676
GND
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
622Mbps, Ultra-Low-Power, 3.3V
Transimpedance Preamplifier for SDH/SONET
MAX3665
ABSOLUTE MAXIMUM RATINGS
V
CC
........................................................................-0.5V to +6.5V
Continuous Current at IN ....................................................±5mA
Voltage at OUT+, OUT- ...................(V
CC
- 1.5V) to (V
CC
+ 0.5V
)
Voltage at FILT ...........................................-0.5V to (V
CC
+ 0.5V)
Continuous Power Dissipation (T
A
= +85°C)
8-Pin µMAX (derate 4.5mW/°C above +85°C) ...........295mW
Operating Junction Temperature (die) ..............-55°C to +150°C
Processing Temperature (die) .........................................+400°C
Storage Temperature Range .............................-55°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
DC ELECTRICAL CHARACTERISTICS
(V
CC
= +3.3V ±10% or +5.0V ±10%, 100Ω load between OUT+ and OUT-, T
A
= -40°C to +85°C. Typical values are at V
CC
= +3.3V,
T
A
= +25°C, unless otherwise noted.)
PARAMETER
Input Bias Voltage
Gain Nonlinearity
Supply Current
Small-Signal Transimpedance
Output Common-Mode Voltage
Differential Output Offset
Output Impedance (per side)
Maximum Output Voltage
Filter Resistor
∆V
OUT
Z
OUT
V
OUT(MAX)
R
FILT
I
IN
= 450µA
P-P
I
IN
= 300µA
48
I
CC
z
21
SYMBOL
V
IN
CONDITIONS
I
IN
= 0 to 300µA
I
IN
= 0 to 10µA
P-P
I
IN
= 0
Differential output
7
21
8
V
CC
- 0.15
±5
50
260
1.5
52
450
MIN
TYP
0.8
MAX
0.95
±5
30
UNITS
V
%
mA
kΩ
V
mV
Ω
mV
P-P
kΩ
AC ELECTRICAL CHARACTERISTICS
(V
CC
= +3.3V ±10% or +5.0V ±10%, 100Ω load between OUT+ and OUT-, source capacitance = 0.5pF, T
A
= -40°C to +85°C. Typical
values are at V
CC
= +3.3V, T
A
= +25°C, unless otherwise noted.) (Notes 1 and 2)
PARAMETER
Small-Signal Bandwidth
Low-Frequency Cutoff
Deterministic Jitter
RMS Noise Referred to Input
Power-Supply Rejection Ratio
J
D
i
n
PSRR
f < 1MHz, differential referred to output,
∆V
CC
= 30mV
P-P
(Note 3)
36
SYMBOL
BW
-3dB
CONDITIONS
Relative to gain at 10MHz
-3dB with I
IN
= 5µA
2
13
- 1 PRBS with 100 CIDs
MIN
404
TYP
470
20
100
55
47
40
260
72
MAX
UNITS
MHz
kHz
ps
nA
dB
Note 1:
AC characteristics are guaranteed by design.
Note 2:
Measured with a 3-pole filter at the output. C
IN
= 0.5pF, I
IN
= 0, C
FILT
= 1000pF.
Note 3:
PSRR = -20log (∆V
OUT
/
∆V
CC
).
2
_______________________________________________________________________________________
622Mbps, Ultra-Low-Power, 3.3V
Transimpedance Preamplifier for SDH/SONET
MAX3665
__________________________________________Typical Operating Characteristics
(V
CC
= +3.3V, includes off-chip filter, see Figure 3b, T
A
= +25°C, unless otherwise noted.)
INPUT-REFERRED NOISE
vs. TEMPERATURE
MAX3665 TOC01
SMALL-SIGNAL GAIN
vs. FREQUENCY
MAX3665 toc02
PULSE-WIDTH DISTORTION
vs. TEMPERATURE (INPUT = 100µA
P-P
)
45
40
35
PWD (ps)
30
25
20
15
10
5
0
V
CC
= 3.3V
V
CC
= 5.0V
MAX3665 toc03
100
90
RMS NOISE CURRENT (nA)
79
78
77
76
GAIN (dB)
75
74
73
72
71
70
69
C
IN
= 1.5pF
50
80
70
60
50
40
30
20
10
0
-40
-20
0
20
40
60
80
C
IN
= 0.5pF
C
IN
IS SOURCE CAPACITANCE PRESENTED TO
DIE. IINCLUDES PACKAGE PARASITIC,
PIN DIODE, AND PARASITIC INTERCONNECT
CAPACITANCE.
C
IN
= 1pF
100
10k
100k
1M
10M
100M
1G
-40
-20
0
20
40
60
80
100
JUNCTION TEMPERATURE (°C)
FREQUENCY (Hz)
AMBIENT TEMPERATURE (°C)
INPUT-REFERRED NOISE
vs. DC INPUT CURRENT
MAX3665 toc04
SMALL-SIGNAL TRANSIMPEDANCE
vs. TEMPERATURE
V
CC
= 5.0V
V
CC
= 3.3V
MAX3665 toc05
PULSE-WIDTH DISTORTION
vs. TEMPERATURE (INPUT = 450µA
P-P
)
45
40
35
PWD (ps)
30
25
20
15
10
V
CC
= 3.3V
MAX3665 toc06
250
SOURCE CAPACITANCE = 0.5pF
RMS NOISE CURRNENT (nA)
8100
8000
TRANSIMPEDANCE (Ω)
7900
7800
7700
7600
7500
7400
50
200
150
100
50
5
0
-40
-20
0
20
40
60
80
100
-40
V
CC
= 5.0V
0
0.1
1
100
DC INPUT CURRENT (µA)
10
1000
-20
0
20
40
60
80
100
AMBIENT TEMPERATURE (°C)
AMBIENT TEMPERATURE (°C)
BANDWIDTH vs. TEMPERATURE
V
CC
= 3.3V or 5.0V
550
BANDWIDTH (MHz)
525
500
475
450
425
400
-40
-20
0
20
40
60
80
100
AMBIENT TEMPERATURE (°C)
MAX2665 toc07
DATA-DEPENDENT JITTER
vs. INPUT SIGNAL AMPLITUDE
MAX3665-08
OUTPUT COMMON-MODE VOLTAGE
(REFERENCED TO V
CC
) vs. TEMPERATURE
-0.11
COMMON-MODE VOLTAGE (V)
-0.12
-0.13
-0.14
-0.15
-0.16
-0.17
-0.18
-0.19
-0.20
V
CC
= 5.0V
V
CC
= 3.3V
MAX3665 toc09
575
160
140
PEAK-TO-PEAK JITTER (ps)
120
100
80
60
40
20
0
0
V
CC
= 3.3V
V
CC
= 5.0V
-0.10
50 100 150 200 250 300 350 400 450
PEAK-TO-PEAK AMPLITUDE (µA)
-40
-20
0
20
40
60
80
100
AMBIENT TEMPERATURE (°C)
_______________________________________________________________________________________
3
622Mbps, Ultra-Low-Power, 3.3V
Transimpedance Preamplifier for SDH/SONET
MAX3665
_____________________________Typical Operating Characteristics (continued)
(V
CC
= +3.3V, includes off-chip filter, see Figure 3b, T
A
= +25°C, unless otherwise noted.)
DIFFERENTIAL OUTPUT AMPLITUDE
vs. TEMPERATURE (INPUT = 450µA
P-P
)
MAX3665 toc10
EYE DIAGRAM
(INPUT = 10µA
P-P
)
MAX3665-11
EYE DIAGRAM
(INPUT = 450µA
P-P
)
MAX3665-12
400
PEAK-TO-PEAK AMPLITUDE (mV)
350
300
V
CC
= 5.0V
V
CC
= 3.3V
250
200
INPUT: 2
13
- 1 PRBS
CONTAINS 100 ZEROS
-40
-20
0
20
40
60
80
100
200ps/div
INPUT: 2
13
- 1 PRBS
CONTAINS 100 ZEROS
200ps/div
150
AMBIENT TEMPERATURE (°C)
_____________________Pin Description
PIN
NAME
V
CC
IN
N.C.
FILT
GND
OUT+
FUNCTION
+3.3V or +5.0V Supply Voltage
Signal Input (From Photodiode)
No Connection. Not internally con-
nected.
On-Chip Resistor for Filtering
Photodiode Supply Voltage
Ground
Noninverting Voltage Output. Current
flowing into IN causes V
OUT+
to
increase.
Inverting Voltage Output. Current flow-
ing into IN causes V
OUT-
to decrease.
IN
Q1
R
F
V
CC
D2
D1
15mV/div
50mV/div
V
CC
1.5kΩ
FILT
1
2
3
4
5, 8
6
V
CC
R1
50Ω
OUT+
Q2
V
CC
PARAPHASE
AMP
R2
50Ω
R5
OUT-
Q3
7
OUT-
V
CC
R7
________________Detailed Description
The MAX3665 is a transimpedance amplifier designed
for 622Mbps SDH/SONET applications. It comprises a
transimpedance amplifier, a paraphase amplifier with
CML differential outputs, and a DC cancellation loop.
Figure 1 shows a functional diagram of the MAX3665.
Q5
REFERENCE AMP
R4
DC
CANCELLATION
AMP
R6
R3
Transimpedance Amplifier
The signal current at IN flows into the summing node of a
high-gain amplifier. Shunt feedback through R
F
converts
this current to a voltage. Diodes D1 and D2 clamp the
output voltage for large input currents.
Q4
MAX3665
GND
Figure 1. Functional Diagram
4
_______________________________________________________________________________________
622Mbps, Ultra-Low-Power, 3.3V
Transimpedance Preamplifier for SDH/SONET
Paraphase Amplifier
The paraphase amplifier converts single-ended inputs to
differential outputs, and introduces a voltage gain. This
signal drives a differential pair of transistors, Q2 and Q3,
which form the output stage. Resistors R1 and R2 provide
back-termination at the output, absorbing reflections
between the MAX3665 and its load.
The differential outputs are designed to drive a 100Ω
load between OUT+ and OUT-. They can also drive
higher output impedances, resulting in increased gain
and output voltage swing.
375MHz and 622MHz. Lower bandwidth causes pat-
tern-dependent jitter and a lower signal-to-noise ratio,
while higher bandwidth increases thermal noise. The
MAX3665 typical bandwidth is 470MHz, making it ideal
for 622Mbps applications.
The preamplifier’s transimpedance must be high
enough to ensure that expected input signals generate
output levels exceeding the sensitivity of the limiting
amplifier (quantizer) in the following stage. The
MAX3676 clock recovery and limiting amplifier IC has an
input sensitivity of 3.6mV
P-P
, which means that
3.6mV
P-P
is the minimum signal amplitude required to
produce a fully limited output. Therefore, when used
with the MAX3665, which has an 8kΩ transimpedance,
the minimum detectable photodetector current is
450nA
P-P
.
It is common to relate peak-to-peak input signals to
average optical power. The relationship between opti-
cal input power and output current for a photodetector
is called the responsivity (ρ), with units amperes per
watt (A/W). The photodetector peak-to-peak current is
related to the peak-to-peak optical power as follows:
I
P-P
= (P
P-P
)(ρ)
Based on the assumption that SDH/SONET signals
maintain a 50% mark density, the following equations
relate peak-to-peak optical power to average optical
power and extinction ratio (Figure 2):
Average Optical Power = P
AVG
= (P0 + P1) / 2
Extinction Ratio = r
e
= P1 / P0
Peak-to-Peak Signal Amplitude = P
P-P
= P1 - P0
MAX3665
DC Cancellation Loop
The DC cancellation loop removes the DC component
of the input signal by using low-frequency feedback.
This feature centers the signal within the MAX3665’s
dynamic range, reducing pulse-width distortion on
large input signals.
The output of the transimpedance amplifier is sensed
through resistors R3 and R4 and then filtered, amplified,
and fed back to the base of transistor Q4. The transistor
draws the DC component of the input signal away from
the transimpedance amplifier’s summing node.
Connect a 400pF or larger capacitor (C
FILT
) between
FILT and case ground for TO header, die-mounted oper-
ation. Increasing C
FILT
improves PSRR. The DC cancel-
lation loop can sink up to 300µA of current at the input.
The MAX3665 minimizes pulse-width distortion for data
sequences that exhibit a 50% mark density. A mark
density other than 50% causes the device to generate
pulse-width distortion.
DC cancellation current is drawn from the input and
adds noise. For low-level signals with little or no DC
component, this is not a problem. Preamplifier noise will
increase for signals with a significant DC component.
___________Applications Information
The MAX3665 is a low-noise, wide-bandwidth transim-
pedance amplifier that is ideal for 622Mbps SDH/
SONET receivers. Its features allow easy design into a
fiber optic module, in three simple steps.
POWER
P1
Step 1: Selecting a Preamplifier for a 622Mbps
Receiver
Fiber optic systems place requirements on the band-
width, gain, and noise of the transimpedance preampli-
fier. The MAX3665 optimizes these characteristics for
SDH/SONET receiver applications that operate at
622Mbps.
In general, the bandwidth of a fiber optic preamplifier
should be 0.6 to 1 times the data rate. Therefore, in a
622Mbps system, the bandwidth should be between
P
AVG
P0
TIME
Figure 2. Optical Power Definitions
5
_______________________________________________________________________________________
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