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

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 1is 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.

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, 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 4shows 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 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.

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.

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 temperature-compensation 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 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.

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.
• 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.

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.

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.

References

[1]

[2]

[3]

Appendix A

MAXIM 3287 Board Layout

1