19-2630; Rev 4; 10/08
6.25Gbps, 1.8V PC Board Equalizer
General Description
The MAX3785 6.25Gbps equalizer operates from a sin-
gle 1.8V supply and compensates for transmission-
medium losses encountered with FR-4 transmission
lines. Optimized for low-voltage, high-density, DC-cou-
pled interconnections between the line card and switch
card, the MAX3785 enables a system upgrade path
while maintaining a legacy rate of 2.5Gbps to
3.125Gbps. Roughly the size of two 0603 passive com-
ponents, the MAX3785 easily provides placement and
routing flexibility.
The MAX3785 is composed of an equalizer, limiting
amplifier, and output driver. For data rates of 3.2Gbps
and lower, the MAX3785 equalizes signals for spans up
to 40in of FR-4 board material. For data rates up to
6.25Gbps, the MAX3785 compensates for 30in of FR-4
board material. The MAX3785 is coding independent,
functioning equally well for 8b/10b or scrambled signals.
The MAX3785 features DC-coupled current-mode logic
(CML) data inputs and outputs. It is packaged in a tiny
1.5mm
×
1.5mm chip-scale package (UCSP™) and a
6-pin TDFN package.
♦
Single 1.8V Supply
♦
Very Low Power, 60mW
♦
Spans 30in with FR-4 at 6.25Gbps
♦
♦
♦
♦
Operates from 1.0Gbps to 6.4Gbps
Coding Independent, 8b/10b or Scrambled
DC-Coupled CML Inputs and Outputs
Small 1.5mm
×
1.5mm Footprint
Features
MAX3785
Ordering Information
PART
MAX3785UBL
MAX3785UWL+
MAX3785UTT
MAX3785UTT+
MAX3785ITT
MAX3785ITT+
TEMP RANGE
0°C to +85°C
0°C to +85°C
0°C to +85°C
0°C to +85°C
-20°C to +85°C
-20°C to +85°C
PIN-PACKAGE
6 UCSP (3
6 WLP
6 TDFN-EP*
6 TDFN-EP*
6 TDFN-EP*
6 TDFN-EP*
3)
+Denotes
a lead-free/RoHS-compliant package.
*EP
= Exposed pad.
Applications
HSBI for
≤
6.4Gbps
Double IEEE 802.3ae XAUI
Double STM-16/OC-48
Δ
A1
IN-
A2
GND
A3
OUT-
Pin Configurations
TOP VIEW (BUMPS ON BOTTOM OF DIE)
IN- 1
6
IN+
GND 2
MAX3785UTT
5
V
CC
MAX3785UBL
UCSP is a trademark of Maxim Integrated Products, Inc.
C1
IN+
C2
V
CC
C3
OUT+
OUT- 3
4
OUT+
3 x 3 UCSP
TDFN
Typical Application Circuit
LINE CARD
BACKPLANE
SWITCH CARD
MAC
1.8V
V
CC
SWITCH
ASIC WITH
SERDES
Rx
Tx
1.8V
6.25Gbps
V
CC
IN
MAX3785
OUT
Rx
Tx
Rx
OUT
MAX3785
IN
30in (0.75m)
Tx
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
6.25Gbps, 1.8V PC Board Equalizer
MAX3785
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, V
CC
to GND.................................-0.5V to +6.0V
Continuous Output Current (OUT+, OUT-) .......-25mA to +25mA
Input Voltage (IN+, IN-) ..............................-0.5V to (V
CC
+ 0.5V)
Operating Ambient Temperature Range
(UBL, UTB)......................................................... 0°C to +85°C
Operating Ambient Temperature Range (ITT).....-20°C to +85°C
Storage Ambient Temperature Range...............-55°C to +150°C
Continuous Power Dissipation (T
A
= +70°C)
6-Pin TDFN (derate 24.4mW above +70°C)..................1.95W
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
(Typical values measured at V
CC
= 1.8V and T
A
= +25°C. Specifications guaranteed over specified operating conditions.)
(See
Operating Conditions
table.)
PARAMETER
Supply Current
Input Swing (IN)
Measured differentially at data source before
encountering loss (Point A in Figure 1) (Note 1)
400
V
CC
-
(IN
MAX
/4)
15
85
450
42
30
50
14
40
0.10
0.15
0.15
0.20
0.75
50
200
(Note 1)
(Note 1)
6.25
6.4
1.0
2.5
55
0.15
0.20
UI
0.25
0.30
1.0
ps
RMS
kHz
ps
Gbps
Gbps
100
115
800
58
dB
ps
mV
P-P
CONDITIONS
MIN
TYP
35
MAX
55
1600
V
CC
-
(IN
MIN
/4)
UNITS
mA
mV
P-P
V
dB
Input Common-Mode Voltage Range (Note 1)
Input Return Loss
Differential Input Resistance
Output Swing
Output Resistance
Output Return Loss
Output Transition Time (t
r
, t
f
)
100MHz to 3.2GHz, power off
IN+ and IN-
Measured differentially at OUT+ and OUT- with 50
±1%
load at each side
OUT+ or OUT-
100MHz to 3.2GHz, IN+ = high
20% to 80% (Note 2)
2.5Gbps, 3.2Gbps, 5.0Gbps; 0in to 30in FR-4
400mV
P-P
IN 1600mV
P-P
Residual Deterministic Jitter
(Notes 1, 3, 4)
2.5Gbps, 3.2Gbps; 40in FR-4
400mV
P-P
IN 1600mV
P-P
6.25Gbps; 0in to 30in FR-4
600mV
P-P
IN 1600mV
P-P
6.25Gbps; 0in to 30in FR-4
IN = 400mV
P-P
Output Random Jitter
Low-Frequency Cutoff Frequency
Latency
Maximum Bit Rate
Minimum Bit Rate
(Notes 1, 2)
Note 1:
Guaranteed by design and characterization.
Note 2:
Using input pattern 0000011111 at 6.25Gbps.
Note 3:
Difference in deterministic jitter between data source and equalizer output, evaluated at 2.5Gbps, 3.2Gbps, 5Gbps, and
6.25Gbps. Pattern used: PRBS (2
7
), ninety-six 0s, 1, 0, 1, 0, PRBS (2
7
), ninety-six 1s, 0, 1, 0, 1.
Note 4:
Signal is applied differentially at input to a 6-mil wide, loosely coupled stripline. Deterministic jitter at the output of the
transmission line is from media-induced loss, not from clock source modulation (see Figure 1).
2
_______________________________________________________________________________________
6.25Gbps, 1.8V PC Board Equalizer
Operating Conditions
PARAMETER
Supply Voltage (V
CC
)
Operating Ambient Temperature (UBL, UTT)
10Hz
≤
f < 100Hz
Supply Noise Tolerance
Bit Rate
Operating Ambient Temperature (ITT)
100Hz
≤
f < 1MHz
1MHz
≤
f
≤
1GHz
NRZ data
2.50
-20
25
CONDITIONS
MIN
1.71
0
TYP
1.8
25
100
40
10
6.25
85
Gbps
°C
mV
P-P
MAX
1.89
85
UNITS
V
°C
MAX3785
PC BOARD
SIGNAL SOURCE
A
3in
≤
L
≤
30in
B
IN
<1.0pF SMA
CONNECTOR
<1.0pF SMA
CONNECTOR
C
OUT
MAX3785
FR-4
4.0 <
ε
r
< 4.4
tanδ = 0.022
Figure 1. Conditions of Testing
Typical Operating Characteristics
(V
CC
= +1.8V, T
A
= +25°C, unless otherwise noted. Measurements done at 6.25Gbps, 500mV
P-P
at the source with a test pattern:
PRBS (2
7
), ninety-six 0s, 1, 0, 1, 0, PRBS (2
7
), ninety-six 1s, 0, 1, 0, 1. Deterministic jitter of the MAX3785 and the board was mea-
sured using Tektronix’s FrameScan™. Deterministic jitter of the system was subtracted from the measured value. Eye diagrams were
acquired by FrameScan, which includes system jitter but eliminates random jitter.)
EYE DIAGRAM OF UNEQUALIZED
SIGNAL AFTER 30in OF FR-4
MAX3785 toc01
EYE DIAGRAM OF EQUALIZED
SIGNAL AFTER 30in OF FR-4
MAX3785 toc02
EYE DIAGRAM OF EQUALIZED
SIGNAL AFTER 30in OF FR-4
MAX3785 toc03
70mV/div
70mV/div
70mV/div
30ps/div
TEST PATTERN, 6.25Gbps,
WITHOUT RANDOM JITTER,
INCLUDING 13ps SYSTEM JITTER
30ps/div
TEST PATTERN, 6.25Gbps,
WITHOUT RANDOM JITTER,
INCLUDING 13ps SYSTEM JITTER
30ps/div
2
10
- 1 PRBS, 6.25Gbps,
WITHOUT RANDOM JITTER,
INCLUDING 13ps SYSTEM JITTER
FrameScan is a trademark of Tektronix.
_______________________________________________________________________________________
3
6.25Gbps, 1.8V PC Board Equalizer
MAX3785
Typical Operating Characteristics (continued)
(V
CC
= +1.8V, T
A
= +25°C, unless otherwise noted. Measurements done at 6.25Gbps, 500mV
P-P
at the source with a test pattern:
PRBS (2
7
), ninety-six 0s, 1, 0, 1, 0, PRBS (2
7
), ninety-six 1s, 0, 1, 0, 1. Deterministic jitter of the MAX3785 and the board was measured
using Tektronix’s FrameScan. Deterministic jitter of the system was subtracted from the measured value. Eye diagrams were acquired
by FrameScan, which includes system jitter but eliminates random jitter.)
EYE DIAGRAM OF UNEQUALIZED
SIGNAL AFTER 30in OF FR-4
MAX3785 toc04
EYE DIAGRAM OF EQUALIZED
SIGNAL AFTER 30in OF FR-4
MAX3785 toc05
EYE DIAGRAM OF EQUALIZED
SIGNAL AFTER 30in OF FR-4
MAX3785 toc06
70mV/div
70mV/div
70mV/div
50ps/div
TEST PATTERN, 3.125Gbps,
WITHOUT RANDOM JITTER,
INCLUDING 13ps SYSTEM JITTER
50ps/div
TEST PATTERN, 3.125Gbps,
WITHOUT RANDOM JITTER,
INCLUDING 13ps SYSTEM JITTER
50ps/div
CRPAT, 3.125Gbps,
WITHOUT RANDOM JITTER,
INCLUDING 13ps SYSTEM JITTER
EQUALIZER OPERATING CURRENT
vs. TEMPERATURE
90
80
70
CURRENT (mA)
JITTER (ps)
60
50
40
30
20
10
0
0
10
20
30
40
50
60
70
80
TEMPERATURE (°C)
MAX3785 toc07
DETERMINISTIC JITTER
vs. BOARD LENGTH (FR-4)
(INPUT LEVEL OF 500mV
P-P
, TEST PATTERN)
MAX3785 toc08
DETERMINISTIC JITTER vs. SIGNAL LEVEL
(TEST PATTERN, 30in OF FR-4 BOARD)
MAX3785 toc09
100
65
60
55
50
45
40
35
30
25
20
15
10
5
10
6Gbps
3.125Gbps
20
15
2.5Gbps
JITTER (ps)
10
3.125Gbps
5
5Gbps
0
15
20
25
30
35
40
0.4
6.4Gbps
2.5Gbps
5Gbps
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
BOARD LENGTH (in)
DIFFERENTIAL SIGNAL LEVEL (V
P-P
)
4
_______________________________________________________________________________________
6.25Gbps, 1.8V PC Board Equalizer
MAX3785
Typical Operating Characteristics (continued)
(V
CC
= +1.8V, T
A
= +25°C, unless otherwise noted. Measurements done at 6.25Gbps, 500mV
P-P
at the source with a test pattern:
PRBS (2
7
), ninety-six 0s, 1, 0, 1, 0, PRBS (2
7
), ninety-six 1s, 0, 1, 0, 1. Deterministic jitter of the MAX3785 and the board was measured
using Tektronix’s FrameScan. Deterministic jitter of the system was subtracted from the measured value. Eye diagrams were acquired
by FrameScan, which includes system jitter but eliminates random jitter.)
DETERMINISTIC JITTER vs. DATA RATE
FOR 10in OF FR-4 BOARD
(INPUT LEVEL OF 500mV
P-P
)
MAX3785 toc10
DETERMINISTIC JITTER vs. DATA RATE
FOR 20in OF FR-4 BOARD
(INPUT LEVEL OF 500mV
P-P
)
2
10
25
CRPAT
20
JITTER (ps)
JITTER (ps)
15
10
TEST
PATTERN
K28.5
2 -1
7
DETERMINISTIC JITTER vs. DATA RATE
FOR 30in OF FR-4 BOARD
(INPUT LEVEL OF 500mV
P-P
)
MAX3785 toc11
-1
25
2
10
- 1
20
JITTER (ps)
15
10
K28.5
5
2
7
0
2.5
3.5
4.5
5.5
6.5
DATA RATE (Gbps)
-1
TEST
PATTERN
CRPAT
25
20
15
10
CRPAT
TEST PATTERN
2
10
- 1
K28.5
2
7
- 1
5
0
2.5
3.5
5
0
4.5
5.5
6.5
2.5
3.5
4.5
5.5
6.5
DATA RATE (Gbps)
DATA RATE (Gbps)
EQUALIZER INPUT RETURN GAIN (SDD11)
(INPUT SIGNAL LEVEL = -40dBm, POWER OFF)
MAX3785 toc13
EQUALIZER INPUT RETURN GAIN (SDD22)
(INPUT SIGNAL LEVEL = -40dBm, IN+ HIGH)
MAX3785 toc14
30
20
10
GAIN (dB)
0
-10
-20
-30
-40
100
1000
FREQUENCY (MHz)
30
20
10
GAIN (dB)
0
-10
-20
-30
-40
10,000
100
1000
FREQUENCY (MHz)
10,000
_______________________________________________________________________________________
MAX3785 toc12
30
30
30
5
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