Download Gigabit Ethernet – IEEE 802

Gigabit Ethernet – IEEE 802.3z
The Choice of a New Generation
Design Report
Javier Alvarez, gte006r
Astou Thiongane, gt3083a
Ebrima Kujabi, gte212s
ECE 4006c
MWF 12:05-1:25pm
Spring 2002
March 26, 2002
Georgia Institute of Technology
College of Engineering
School of Electrical and Computer Engineering
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Introduction
As the number of computer users increases over the years and the demand for high-speed
data transmission increases exponentially, the need to design a medium that can meet the
demand of the users becomes obvious. The trend for such a medium went from Ethernet to Fast
Ethernet. However, these protocols could no longer keep up with the pace over a few years;
hence, there was the desire to design a faster, more efficient and cost effective medium – Gigabit
Ethernet. This need defines the goal for this project, which includes building our own functional
opto-electronic transmitter and fitting it onto an operational Gigabit Ethernet network card.
The first step includes testing, evaluating and analyzing the new MAXIM 3287 chip and
understanding the functionalities of each component. This, in turn, will allow us to identify
which components are needed in order to eventually build our own board. In order to build a
cost-effective board, the best prices will be researched. The second step will be to look for an
emitter that can give optimal speed, low cost and optimal emitting capacity. The VCSEL was
chosen because it has these characteristics and it also works well with the MAXIM3287
evaluation board. Once the emitter has been chosen, a detector will be selected. The PIN diode,
photodetector, will be the ideal selection because of its low cost, high speed and high sensitivity.
In addition, we will use SMA cables because of its durability, higher bandwidth, and lack of
signal interference caused by noise. Once we have all these parts, we will then proceed to build
our own opto-electronic transmitter. Finally, the board will be tested by comparing it to an IEEE
eye-diagram in order to indicate if the system has an acceptable signal-to-noise ratio (SNR).
Intel Card/Opto-Module
In order to ensure for the design and testing of the Ethernet card, a better understanding
of the Intel Card is needed. In this part, we will first explain the function of the different pins on
the module, then the function of the different electric parts on it. Figure 1 is a graphical
representation of the connections on the module. The pins on the Figure are
Figure 1. Top View of the Connections of the Opto-module.
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labeled from 1 to 9. The function of each pin is the following:
-
Pins 1 and 9 respectively stand for the grounds for the receiver and transmitter.
-
Pins 2 and 3 are the receiver differential output.
-
Pin 4 is the Signal Detect, which provides the information about the link being open or
the transmitter being off.
-
Pins 5 and 6 provide respectively the transmitter and receiver powers.
-
Pins 7 and 8 are the differential transmitter outputs.
This figure gives an insight about how to connect components to the module but a closer look at
the card is needed in order to understand it fully as well as to assess the requirements of the
group’s part of the design. Figure 2 is a representation of the opto-module as it is connected to
the Intel card.
Figure 2. Opto-Module Connected to Intel Card
As Figure 2 illustrates it, the elements in the dashed box constitute the opto-module, which is a
transceiver. The top circuit, i.e. the one with the laser driver is the transmitter while the bottom
circuit is the receiver. The section of the circuit that is in the circle is a filter for the noise
coming from the dc power supply to the transmitter and receiver. Resistors 1 through 4 are in
parallel in ac and therefore provide a 50-Ohm termination to the cables. The capacitors C9, C10,
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C11 and C12 provide a dc coupling to the lines they are connected to. On the illustration, Figure
3, we can see how the opto-module is connected to the Intel network card.
Figure 3. The Opto-Module as it Connects to the Intel card [1].
In the white box on the figure above, the opto-module with its 9 pins is the same as the
illustration in Figure 1. For the needs of our project, the module was separated into a transmitter,
a receiver and a laser driver. Our group was assigned the transmitter but needs to fit its design to
the needs of the groups working on the receiver and the laser driver. Figure 4 shows how the
three parts will fit together once completed.
Figure 4. High Level Drawing of the Reconstructed Opto-Module
MAXIM Board Specifications
Reverse Engineering might seem to be unethical and unprofessional, but it is the exact
opposite. It is an essential ingredient to produce more reliable and inexpensive technology, not
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to mention a great learning tool for up and coming engineers. For this reason, one of the primary
goals of this project is to analyze a Maxim transmitter board in order to produce our own from
the ground up. The MAXIM 3287 evaluation kit will be used as the optical transmitter on an
Intel PRO/1000 Ethernet card. This board is optimized for operation at 1.25 Gbps and can
support 30mA of laser modulation current at the specified data rate. Also, the deterministic jitter
(DJ) for the MAX3287 is approximately 22ps.
Maxim 3287 Chip
The main component located on the board is the Maxim 3287 chip. This 16-pin chip,
shown in Figure 5, controls the operation of the laser.
Figure 5. MAX3287 Laser Driver Chip [2].
The following is a brief description of the different pin assignments found on this chip.

Pin 1 and 6 are ground (GND).

Pin 2 is the power-on reset (POR). This feature is used to reset the laser when it has been
turned off due to safety features incorporated into the chip. A POR signal turns low
when VCC is within the operating range of 3 to 5 Volts. Also, POR contains an internal
delay to reject noise on VCC during power-on or hot-plugging.

Pins 3, 11, and 14 labeled as VCC are connected to a 3 to 5 Volt power supply.

Pin 4 and pin 5 are the non-inverting (IN+) and inverting (IN-) input, respectively.

Pin 12 (OUT+) and pin 13 (OUT-) are the modulation-current outputs. Figure 6
illustrates the differential input, resulting signal, and modulated current output.
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Figure 6. Plot of the differential input, resulting signal, and modulated current [2].
The main reason for using differential inputs is to eliminate noise that may have occurred
during transmission. When the non-inverting input is subtracted from the inverting input,
the original signal is obtained with an amplitude size two times that of the original signal.

Pin 7 is the reference voltage (REF). The reference voltage should be set to VREF = 2.65
– 2.25(VCC – VMON), where VMON is the voltage across the laser bias current
monitor. This is primarily used for programming laser bias current in VCSEL
applications. In addition, a resistor connected at REF determines the laser power when
automatic power control is used with common-cathode lasers.

Pin 8 is the monitor diode (MD) connection. MD is used for automatic power control of
the laser; however, this feature is not available on the MAX3287 board.

Pin 9 is the shutdown driver output (SHDNDRV). This is another safety feature included
with the MAX3287 chip, which shuts down the laser.

Pin 10 is the bias-controlling transistor driver (BIASDRV). A capacitor must be placed
from BIASDRV to VCC to ensure low-noise operation and to reject power-supply noise.
However, this feature is used only with optical feedback which is not included with this
board.

Pin 15 is the modulation-current set (MODSET) and pin 16 is the temperaturecompensation set (TC). The amplitude of the modulation current is set with resistors at
the MODSET and temperature coefficient (TC) pins. The resistor at MODSET controls
the temperature-stable portion of the modulation current, while the TC pins control the
increasing temperature due to the modulation current. Table 1 on the next page shows
several different types of resistance configurations in order to obtain a given modulation
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current. In addition, several different equations can be used to determine these
resistances. Equation 1 determines the temperature coefficient based on the slope
efficiency () of a given laser at 70 C and 25 C. While, Equations 2 and 3 are used to
determine the resistances for the TC and MODSET input pins.
(Eq. 1)
(Eq. 2)
(Eq. 3)
Table 1. RTC and RMOD Selection Table [2].
Maxim Board Layout Analysis
The following list contains a complete analysis of the Maxim board layout as shown in
Appendix A. There are two different layouts on the evaluation board – the stuffed and unstuffed
layout. The stuffed layout consists of more components because it utilizes some of the safety
features incorporated on the Maxim chip (U2). The unstuffed layout, on the other hand, in U3 is
less cluttered because it eliminates the use of certain safety features.

The transistor Q1 acts as a switch to turn the laser on and off; however, this feature
will not be used.
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
Since the laser will not be mounted on the MAX3287 Evaluation board, the following
components will not be needed: U5, Q6, R5, R9, R10, R24, R37, R38, D1.

Q2, L3, and R11 are used to control the current needed to drive the laser via the SMA
cable connected to J15.

Decoupling capacitors (C1, C2, C3, C4, C11, C12, C13, C14, C22, C23, C40, C52)
act as an open circuit when a dc bias is applied and a short circuit when ac biased.

Finally as mentioned before, RMOD and RTC are needed to control the current
modulation and the temperature coefficient of the laser.
Board Set-Up
Our first task in this project is to set-up the Maxim board for proper operation with the
Intel/PRO 1000. The Maxim board can be configured in several different ways, but in this
project the common-cathode laser configuration will be used. Appendix A contains a schematic
of the board layout used in this project. The following 12-step process will be implemented to
prepare the board.
1) Connect pins 1 and 6 to ground.
2) A jumper should be placed on JU1. This essentially connects pin 2 (Fault Delay) to
ground, which disables the safety features incorporated in the MAX3287 chip.
3) Apply +5V power to the board at J1 (VCC) and J2 (GND) test points.
4) Set the R3 (RTC) potentiometer to maximum resistance. This minimizes the temperature
coefficient of the modulation current.
5) Set the R4 (RMOD) potentiometer to maximum resistance by turning the screw
completely counterclockwise (approximately 50 k). This minimizes the modulation
current.
6) Place a jumper between pins 1 and 2 on JU3 to provide power to the main circuit.
7) Remove R24 (24.9 ) and replace it with R20 (49.9 ).
8) Attach differential sources to SMA connectors J4 and J5. Each source should have a
peak-to-peak amplitude between 100mV and 830mV.
9) Connect an SMA cable from J15 (OUT-) to the laser module. This output will be used to
drive the laser. In order for the current to be large enough to drive the laser, the PNP
transistor attached to pin 5 (BIASDRV) must be biased correctly.
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10) While monitoring the laser output, adjust R4 (RMOD) until the desired laser modulation
current is obtained.
11) While monitoring the laser output, adjust R4 (RMOD) until the desired laser
modulation current is obtained.
12) Look at the eye output on an oscilloscope capable of supporting frequencies of up to at
least 1.25 GHz, such as the Tektronix TDS7154 DPO, 1.5 GHz, 20 GS/sec.
Building our own Board
One of the goals of this project will be to build our own board. The first part involved
analyzing the new Maxim board and understanding how it worked. After this careful analysis,
the following circuit in Figure 8 was designed.
Figure 8. Schematic of proposed circuit design.
As shown on the top left of Figure 8, the power supply is being regulated to supply a steady
voltage of 5 Volts, as well as filtering out any noise due to the power supply. Also, all of the
safety features and on-board laser biasing components attached to pins 7, 8, 9, and 10 were
removed. Since the laser will be driven via the SMA connector (J15), there is no need for the
transistors and it’s biasing components because they were only used to provide a certain
threshold current for a laser mounted on the Maxim board. The following table, Table 2, is a list
of components that will needed in order to complete the design of our own board.
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Description
Component
Value
Quantity
Resistors (1206)
(Surface Mount)
Resistors (1206)
(Surface Mount)
Resistors (1206)
(Surface Mount)
Resistors (1206)
(Surface Mount)
Resistors (1206)
(Surface Mount)
Trimmer Potentiometers
(3296W)
Capacitors (1206)
(Ceramic Chip)
Capacitors (1206)
(Ceramic Chip)
Capacitors (1206)
(Ceramic Chip)
Ferrite Bead Inductor
(BLM11HA102SG)
Inductor (1206)
SMA Connectors
Power Supply Connector
MAXIM3287 Chip
68
2
191
2
115
1
49.9
1
68
2
200k
2
0.1F
3
0.01F
5
10F
1
N/A
2
1H
N/A
N/A
N/A
1
3
1
1
Table 2. Required Component List.
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References
[1] http://www.ece.gatech.edu/academic/courses/fall2001/ece4006/1G3/fulldesign.doc
[2] http://pdfserv.maxim-ic.com/arpdf/MAX3286-MAX3299.pdf
[3] http://pdfserv.maxim-ic.com/arpdf/MAX3287EVKIT.pdf
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Appendix A
MAXIM 3287 Board Layout
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