19-3181; Rev 0; 2/04
3.2Gbps SFP Transimpedance
Amplifiers with RSSI
General Description
The MAX3724/MAX3725 transimpedance amplifiers pro-
vide a compact, low-power solution for communication
up to 3.2Gbps. They feature 325nA input-referred noise
at 2.1GHz bandwidth (BW) with 0.6pF input capaci-
tance. The parts also have >2mA
P-P
AC input overload.
Both parts operate from a single +3.3V supply and con-
sume 93mW. The MAX3724/MAX3725 are in a compact
30-mil x 50-mil die and require no external compensa-
tion capacitor. A space-saving filter connection is pro-
vided for positive bias to the photodiode through an
on-chip 580Ω resistor to V
CC
. These features allow
easy assembly into a low-cost TO-46 or TO-56 header
with a photodiode.
The MAX3724 and MAX3748A receiver chip set pro-
vides an RSSI output using a Maxim-proprietary* inter-
face technique. The MAX3724 preamplifier, MAX3748A
postamplifier, and the DS1858/DS1859 SFP controller
meet all the SFF-8472 digital diagnostic requirements.
Features
♦
Wider Bandwidth than MAX3744/MAX3745
♦
RSSI Implementation in 4-Pin TO-46 Header
(MAX3724 and MAX3748A)
♦
8ps
P-P
Deterministic Jitter for <100µA
P-P
Input
Current
♦
325nA
RMS
Input-Referred Noise at 2.1GHz
Bandwidth
♦
28mA Supply Current at +3.3V
♦
2.5GHz Small-Signal Bandwidth
♦
2.0mA
P-P
AC Overload
♦
Die Size: 30 mils x 50 mils (Identical to the
MAX3744/MAX3745)
MAX3724/MAX3725
Applications
Up to 3.2Gbps SFF/SFP Optical Receivers
Optimized for Small-Form-Factor Pluggable (SFP)
Optical Receivers
*Patent
pending.
PART
MAX3724E/D
MAX3725E/D
Ordering Information
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
Dice**
Dice**
**Dice
are designed to operate with junction temperatures of
-40°C to +110°C but are tested and guaranteed only at T
A
=
+25°C.
Typical Application Circuit
SFP OPTICAL RECEIVER
V
CC
400pF
400pF
V
CC
V
CC
FILTER OUT+
MAX3724
OUT-
IN
GND
IN+
MAX3748A
IN-
OUT-
RSSI
4-PIN TO CAN
3.3k
Ω
MOD-DEF1
DS1858/
DS1859
0.1
µ
F
OUT+
0.1
µ
F
HOST
BOARD
V
CC
= 3.3V
4.7kΩ
TO
10kΩ
DISABLE
LOS
MOD-DEF2
________________________________________________________________
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.
3.2Gbps SFP Transimpedance
Amplifiers with RSSI
MAX3724/MAX3725
ABSOLUTE MAXIMUM RATINGS
Power-Supply Voltage (V
CC
) .................................-0.5V to +6.0V
Continuous CML Output Current
(OUT+, OUT-) ............................................. -25mA to +25mA
Continuous Input Current (IN)...............................-4mA to +4mA
Continuous Input Current (FILTER).......................-8mA to +8mA
Operating Junction Temperature Range (T
J
) ....-55°C to +150°C
Storage Ambient Temperature Range (T
STG
) ...-55°C to +150°C
Die Attach Temperature...................................................+400°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.
ELECTRICAL CHARACTERISTICS
(V
CC
= +2.97V to +3.63V and T
A
= -40°C to +85°C. Typical values are at V
CC
= +3.3V, source capacitance (C
IN
) = 0.85pF, and T
A
=
+25°C, unless otherwise noted.) (Notes 1, 2)
PARAMETER
Supply Current
Input Bias Voltage
Input Overload
(Note 3)
C
IN
= 0.85pF, BW = 933MHz
C
IN
= 0.85pF, BW = 2.1GHz (Note 3)
Input-Referred Noise (Note 4)
I
N
C
IN
= 0.85pF, BW = 18GHz (Note 3)
C
IN
= 0.6pF, BW = 933MHz
C
IN
= 0.6pF, BW = 2.1GHz (Note 3)
C
IN
= 0.6pF, BW = 18GHz (Note 3)
Differential Transimpedance
Small-Signal Bandwidth (Note 3)
Low-Frequency Cutoff
Deterministic Jitter
(Notes 3, 5)
Filter Resistance
Differential Output Resistance
(OUT+, OUT-)
Maximum Differential Output
Voltage
V
OD
Input > 50µA
AVE
, output termination 50Ω to
V
CC
(output in limited state)
BW
Differential output, I
IN
= 40µA
AVE
-3dB, C
IN
= 0.6pF
-3dB, C
IN
= 0.85pF
-3dB, input current = 20µA
AVE
(Note 3)
100µA
P-P
< input
≤
2.1Gbps, K28.5 pattern
2mA
P-P
2.7Gbps, 2
31
- 1 pattern
10µA
P-P
< input
≤
100µA
P-P
2.1Gbps, K28.5 pattern
2.7Gbps, 2
31
- 1 pattern
510
85
220
11
15
8
12
580
100
280
690
115
400
Ω
Ω
mV
P-P
17
2.8
2
1.8
3.5
2.5
2.3
30
33
ps
P-P
200
325
440
635
4.5
kΩ
GHz
kHz
2
200
360
485
700
nA
RMS
SYMBOL
I
CC
CONDITIONS
Including CML output current (I
IN
= 0)
MIN
TYP
28
MAX
41
1.0
UNITS
mA
V
mA
P-P
DJ
2
_______________________________________________________________________________________
3.2Gbps SFP Transimpedance
Amplifiers with RSSI
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +2.97V to +3.63V and T
A
= -40°C to +85°C. Typical values are at V
CC
= +3.3V, source capacitance (C
IN
) = 0.85pF, and T
A
=
+25°C, unless otherwise noted.) (Notes 1, 2)
PARAMETER
Single-Ended Output Common-
Mode Minimum Level (MAX3724)
Output Data Transition Time
Differential Output Return Loss
Power-Supply Noise Rejection
RSSI Gain (MAX3724)
RSSI Gain Stability (MAX3724)
PSNR
A
RSSI
SYMBOL
CONDITIONS
Relative to V
CC
, I
IN
= 1mA
AVE
Input > 200µA
P-P
20% to 80% rise/fall time
(Note 3)
Frequency
≤
1GHz
1GHz < frequency
≤
2GHz
I
IN
= 0
(Note 6)
(Note 7)
10log(A
RSSI
/A
RSSI-NOM
) where A
RSSI-NOM
=
A
RSSI
at 3.3V, +25°C (Note 3)
f < 1MHz
1MHz
≤
f < 10MHz
MIN
540
TYP
490
70
17
10
46
34
21
0.24
100
MAX
UNITS
mV
ps
dB
dB
A/A
dB
MAX3724/MAX3725
Note 1:
Dice are designed to operate with junction temperatures of -40°C to +110°C but are tested and guaranteed only at T
A
= 25°C.
Note 2:
Source capacitance represents the total capacitance at the IN pad during characterization of the noise and bandwidth para-
meters.
Note 3:
Guaranteed by design and characterization.
Note 4:
Input-referred noise is:
RMS output noise
Gain at f
=
100MHz
Note 5:
Deterministic jitter is the sum of pulse-width distortion (PWD) and pattern-dependent jitter (PDJ).
Note 6:
Power-supply noise rejection PSNR = -20log(∆V
OUT
/
∆V
CC
), where
∆V
OUT
is the differential output voltage and
∆V
CC
is the
noise on V
CC
.
Note 7:
I
OUT _ CM
(I
IN
=
400
µ
A)
−
I
OUT _ CM
(I
IN
=
0
µ
A)
A
RSSI
=
400
µ
A
+
I
OUT
−
I
where I
OUT _ CM
=
OUT
+
2
RSSI range is from I
IN
=
6
µ
A to 500
µ
A
_______________________________________________________________________________________
3
3.2Gbps SFP Transimpedance
Amplifiers with RSSI
MAX3724/MAX3725
Typical Operating Characteristics
(V
CC
= +3.3V, C
IN
= 0.85pF, T
A
= +25°C, unless otherwise noted.)
INPUT-REFERRED NOISE
vs. TEMPERATURE
MAX3724/25 toc01
INPUT-REFERRED NOISE
vs. TEMPERATURE
BW = 2.1GHz
INPUT-REFERRED NOISE (nA
RMS
)
700
600
GAIN (dB)
500
400
300
200
MAX3724/25 toc02
OPTICAL FREQUENCY RESPONSE
(70µm InGaAS PHOTODIODE, INPUT -22dBm)
35
30
25
20
15
10
5
0
MAX3724/25 toc03
800
UNFILTER
INPUT-REFERRED NOISE (nA
RMS
)
700
600
500
400
300
200
-40
-20
0
20
40
60
80
C
IN
= 0.5pF
C
IN
= 1.5pF
C
IN
= 0.85pF
800
40
C
IN
= 1.5pF
C
IN
= 0.85pF
C
IN
= 0.5pF
-5
100
-10
100M
1G
FREQUENCY (Hz)
10G
100
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
TEMPERATURE (°C)
DETERMINISTIC JITTER
vs. INPUT VOLTAGE
MAX3724/25 toc04
SMALL-SIGNAL TRANSIMPEDANCE
vs. TEMPERATURE
MAX3724/25 toc05
EYE DIAGRAM
INPUT = 20µA
P-P
, DATA RATE = 2.1Gbps
MAX3724/25 toc06
50
45
DETERMINISTIC JITTER (ps
P-P
)
40
35
30
25
20
15
10
5
0
0.01
0.1
1
2.1Gbps, K28.5
2.7Gbps, 2
7
-1PBRS
75
K28.5 PATTERN
TRANSIMPEDANCE (dB
Ω)
70
10mV/div
65
10
60
-40
-20
0
20
40
60
80
100
TEMPERATURE (°C)
60ps/div
INPUT CURRENT (mA
P-P
)
EYE DIAGRAM
INPUT = 20µA
P-P
, DATA RATE = 3.2Gbps
MAX3724/25 toc07
EYE DIAGRAM
INPUT = 2mA
P-P
, DATA RATE = 2.1Gbps
MAX3724/25 toc08
EYE DIAGRAM
INPUT = 2mA
P-P
, DATA RATE = 3.2Gbps
MAX3724/25 toc09
K28.5 PATTERN
K28.5 PATTERN
K28.5 PATTERN
10mV/div
50mV/div
50mV/div
50ps/div
60ps/div
50ps/div
4
_______________________________________________________________________________________
3.2Gbps SFP Transimpedance
Amplifiers with RSSI
MAX3724/MAX3725
Typical Operating Characteristics (continued)
(V
CC
= +3.3V, C
IN
= 0.85pF, T
A
= +25°C, unless otherwise noted.)
SUPPLY CURRENT
vs. TEMPERATURE
MAX3724/25 toc11
MAX3724/25 toc10
DIFFERENTIAL S22 vs. FREQUENCY
0
-5
MAX3724
-10
S22 (dB)
-15
-20
-25
-30
0
500 1000 1500 2000 2500 3000 3500 4000
FREQUENCY (MHz)
MAX3725
70
60
SUPPLY CURRENT (mA)
50
40
30
20
10
0
-40
-20
DC TRANSFER FUNCTION
(V
FILT
= 0V)
150
OUTPUT VOLTAGE (mV
P-P
)
100
50
0
-50
MAX3724/25 toc12
200
-100
-150
-200
0
20
40
60
80
100
-100
-50
0
50
100
TEMPERATURE (°C)
INPUT CURRENT (mA
P-P
)
RSSI
MAX3724, MAX3748A
MAX3724/25 toc13
BANDWIDTH vs. TEMPERATURE
MAX3724/25 toc14
EYE DIAGRAM
TEMPERATURE = +100°C INPUT = 20µA
P-P
DATA RATE = 2.7Gbps
MAX3724/25 toc15
550
500
MAX3748 RSSI OUTPUT (µA)
450
400
350
300
250
200
150
0
T
A
= -40°C
4
2
23
- 1 PRBS
T
A
= +85°C
3dB BANDWIDTH
3
MAX3724 C
IN
= 0.6pF
2
MAX3744 C
IN
= 0.6pF
6mV/div
1
0
500
1000
1500
2000
-40
-20
0
20
40
60
80
100
60ps/div
AVERAGE INPUT CURRENT (µA)
TEMPERATURE (°C)
OPTICAL EYE DIAGRAM
INPUT = 0dBm, DATA RATE = 3.2Gbps
MAX3724/25 toc16
OPTICAL EYE DIAGRAM
INPUT = 0dBm, DATA RATE = 4.25Gbps
MAX3724/25 toc17
OPTICAL EYE DIAGRAM
INPUT = -18dBm, DATA RATE = 4.25Gbps
MAX3724/25 toc18
K28.5 PATTERN
K28.5 PATTERN
K28.5 PATTERN
100mV/div
30mV/div
3mV/div
60ps/div
60ps/div
50ps/div
_______________________________________________________________________________________
5
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