1. INTRODUCTION:

A GIGABIT Ethernet card is a Network Interface installed in PCs and Servers to connect multiple PCs and Servers for data communication purposes. Gigabit refers to the speed of communication achieved by the controller used – 1.0 Gigabits per second. A Gigabit Ethernet card once installed in a server is usually connected to a Gigabit switch which are available in multiple configurations of 8 / 16 / 24 /48 port switches. Ethernet cards are based on controllers that are designed by Controller manufacturing companies i.e. Intel, Broadcom, Chelsio, Solar Flare, Qlogic, Realtek, Marvell, etc. These controllers are based on standards released by IEEE. The standard is usually referred to as IEEE 802. This helps the pharmaceutical industry for faster clinical evaluations. The Ethernet card implements the electronic circuitry required to establish the communication required between specific physical layer and data link layer which are utmost important for medical purposes. The standard defines the communication are optical fiber channel, Ethernet, Token Ring, Wi-Fi etc.

This serve as a base for a full network protocol stack for distribution process. The network protocol allows communication in LAN and large-scale network. The communications usually happens through small group of computers. One such a reusable protocol is Internet Protocol (IP) and Simple Object Access Protocol (SOAP)¹.

The Ethernet adapters for gigabit communication represent the future step in the evolution performance of the pharmaceutical industries. Gigabit Ethernet delivers performance beyond the aggregation band-aids by delivering speeds approaching 1Gbps there by producing faster products². This enables further pharmacy industry to use social media and/or e-commerce sites for digital marketing³. With the development of faster Ethernet card, customers and patients will have easy procurement of pharmaceutical products and saves lives of humans and other organisms.

2. BOARD CREATION PROCESS:

The board creation process involves following three major steps.

A. Schematics Capture:

This step provides us with the overall logical flow of the design. All the interconnection between the components are shown in detail. Each component in the schematics has a unique symbol; this symbol is created in accordance with the pin out diagram which is specified in the manufacturer datasheet.

The properties of each of the symbols must be mentioned (Part number, Vendor part number, Description etc.).This will help in creating the BOM (Bill of Materials) with ease.

B. Footprint Creation:

The footprint of a device is a board level representation of the exact dimensions of the conductive pads of the device and the distance between each pad. This is also called land pattern of the device. A lot of care must be taken during creation of footprint as any mistake can lead to one or more of the pads of a component becoming unable to conduct signals and this may compromise the entire design of the board.

There are many packages available in the market for similar components and care must be taken in choosing a component package for a specific application

C. Layout and Routing:

In this stage we place the components in accordance to the logical flow as shown in the schematics (layout) and connect them with traces, the thickness of which is determined by the amount of current each trace is carrying(routing).

This stage is very important from a high speed digital design perspective as most of the rules and constraints for high speed boards is to be applied in this stage. Some examples are spacing between components, Length of the differential traces, placement of critical components etc.

3. SCHEMATICS GUIDELINES:

The gigabit Ethernet controller needed for the design should be identified and the datasheet of the same should be available. Study the datasheet of the controller carefully and make the symbol for the same in the schematic capture tool according to the pinout diagram given in the datasheet. Most of the time the controller has too many pins to represent in a single symbol, therefore the symbol is split into different parts (corresponding to a function).

This type of symbol is called a heterogeneous package symbol. Most of the controller manufacturers provide a reference schematic and recommended design guidelines along with the controller datasheet. These guidelines must be followed and implemented strictly in order to maintain the integrity of the design and ensure the proper working of the finished PCB.

Fig 1: Simple block diagram of the system.

Fig 2: Schematic for a crystal and clocking circuit.

The reference schematics provided is for LAN on motherboard application and therefore suitable changes must be made in order to implement a HBA using the same designs. The changes required involve adding a PCIe interface to the design. The width of the edge connector (PCIe connector) depends on the requirement of the controller and refers to the application guidelines for information on the same.

PCIe electrical specifications must be referred to for the edge connector pinouts and signal information. The PCIe specification also includes the length and breadth of the board required to meet various form factors followed in the industry like low profile, full height etc. The power requirements for the controller should be studied carefully and implemented as per industry standard for high speed signals, with necessary amount of decoupling capacitors.

4. DESIGN:

A crystal based oscillator circuit is shown in figure 2.The correct operation of the crystal oscillator is dependent on the on the values of the two external capacitors, C1 and C2. These capacitors together with any parasitic capacitance in the PCB and the crystal terminals compose the total load capacitance seen by the crystal^4,5. A crystal is usually tuned to a specific load capacitance. The load capacitance is primarily determined by the specified frequency. It is the total external capacitance across the crystal leads and is determined by the below equation.

C1 X C2

Cload =Cs + ---------

C1 + C2

Cs is the board stray capacitance and is typically between 2pf and 5pf. In the typical implementation C1=C2, so the crystal load capacitance equation is as shown below where C1=C2=C. The equation is

Cload =Cs + 0.5 C

5. LAYOUT AND ROUTING GUIDELINES:

A. Rj45 and Magnetics:

RJ-45(Registered Jack- 45) is an eight wire connector which is normally used to connect computers to a local area network (LAN), especially Ethernet. Magnetics is used in the Ethernet NIC’s for the purpose of isolation and ground offset. The magnetics should be located as close as possible to the RJ-45connector. The magnetics provides EMI and ESD isolation between the main controller and the RJ45 cable connection to the outside⁶. The magnetics should be placed as close as possible to the controller and the designer should keep in mind that better ESD performance can be achieved by opting for a separate magnetics and RJ45 topology as compared to integrated magnetics in RJ45. The differential pairs arising out of the controller to the magnetics and the magnetics to the RJ45 should be routed with a controlled impedance of 100ohms⁶.

An RJ45 connector with surface mount contacts can be opted for to simplify routing of the signals. All impedance controlled signals must be routed in reference to a solid low noise plane, preferably the ground plane⁷. None of the traces should have 90deg bends. The end to end trace length between each differential must match within a specified distance as mentioned by the controller manufacturer (usually 5 mils).The end to end trace length is defined as the total length from one component to another regardless of the layer transition. If the pair length matching is not possible using bends and small loops, then serpentine routing can be used. Serpentine routing to RJ45 connector which connects to large out-of-system unshielded cables can contribute to radiate EMI and can decrease immunity to ESD.

Pair to pair difference in length is not critical. A 25% difference in length from the longest pair to the shortest pair is typical. Paired 50ohms trace does not make 100 ohms differential. A differential calculator can be used to verify this. Manufacturer must be consulted for the stack up details.

B. PCIe Interface:

PCIe stands for peripheral component interconnect express. PCI Express was developed by Intel Corp. in 2004 to replace the peripheral component interconnect (PCI). The PCIe differential pairs must be routed with 85ohm impedance trace for data signal and 100ohm impedance trace for REFCLK. All impedance controlled signals must be routed in reference to a solid plane^7,8. The AC coupling capacitors should be placed very close to the transmit or receive side. It is recommended to increase the distance between differential pair AC coupling capacitors to at least 30 mils to reduce the package to package parasitic.

6. POWER SUPPLY CONSIDERATION AND DECOUPLING:

High speed circuits generally consume more power than low speed circuits. This means that the power supply system on the board must be able to handle the increased demand of the current flow. The best practice followed in the industry with regards to layout of the high speed board is that the highest speed devices have the shortest trace lengths. Decoupling methods can be divided into two stages:

· Power entry decoupling

· Chip level decoupling

Power entry capacitors are large valued capacitors (100uF or larger). The purpose of these capacitors is to make sure that a stable voltage is maintained at the power entry point⁶. In high speed digital systems chip level decoupling capacitors (0.1uF or 0.01uf) are used to eliminate high speed switching noise by providing a path to ground for the high speed noise⁹.They are also known as bypass capacitors^6,10.

7. PCB MATERIAL:

FR-4 (or FR4) is a classification assigned to reinforced glass epoxy laminate sheets. It can also be classified as Printed Circuit Boards (PCB), tubes, etc. The material FR-4 usually composed of woven fiberglass cloth. The cloth is an epoxy resin binder that is flame resistant. The term "FR" stands for flame retardant.

The specialty is that it specifies the safety of flammability of FR-4 which is in compliance with the standard UL94V-0. In 1968 NEMA formed FR-4 from the constituent materials (epoxy resin, woven glass fabric reinforcement, brominated flame retardant, etc.). Since the FR-4 having good strength to weight ratio, it one the most popular and versatile high-pressure thermoset plastic laminate grade in PCB fabrication. The material is known to its capability to retain insulating electrical quality and high mechanical values in both dry and humid conditions. FR-4 and other insulating laminate grades are regulated by NEMA. Popular grade designations are G10, G11, FR4 and FR5. Out of all these, FR4 is used today in most industries. The grade G-10 is predecessor to FR-4, and lacks self-extinguishing flammability characteristics. These materials are used to make boards with high speed characteristics. High glass transition temperature characteristics Tg are usually required for high speed characteristics. Once the temperature exceeds threshold glass transition temperature Tg, the characteristic of the board change from glassy state to rubbery state. If the state changes, then the function of board will be affected. Famous high glass temperature Tg materials which are available in the market are shengyi technologies S1170&S1000-2¹¹, and Hitachi’s Mica-AVA, MCL-E-679¹². Another popular Material is 370HR. It is having a glass transition temperature of 180°C.

The material 370HR is a unique high performance multifunctional epoxy resin. It is reinforced with E-glass electrical grade fabric. Compared to FR-4, 370HR provides good thermal performance and low expansion rates. Moreover, it is having good mechanical, chemical and moisture resistance properties which are required for high speed PCB fabrication. 370HR provides maximum compatibility by blocking UV¹³.

8. PCB FINISH:

Printed circuit boards will have copper finish on their surface. If boards are left unprotected, copper on the surface will oxidize and deteriorate. If the copper oxidizes, the boards are not usable. Between the board and components, the surface finish act as a critical interface. Essential functions of the finish are to safeguard the exposed circuitry and to provide a solderable surface for assembling¹⁴.

9. CONCLUSION:

It is important to follow all the high speed guidelines mentioned above while attempting to design a high speed NIC (network interface card). Different controller manufacturers may have different guidelines to be followed for their specific controller; therefore it is very important to go through the datasheet of the controller and the supporting documents provided by the controller manufacturer carefully before attempting a design for pharmaceutical applications like drug delivery, biomedical applications, image transfer and chemical analysis etc. It is important to opt for the appropriate surface finish by exploring various options while for performance requirements and material costs.

10. REFERENCES:

1. H. T. Gao, J. H. Hayes and H. Cai. Integrating biological research through Web services. Computer, 2005: 38(3): 26-31.

2. White Paper on GA620/GA620T Gigabit Ethernet Card Performance. Available from URL: ftp://downloads. netgear. com/files/ga620wp.pdf

3. Dhara Parekh, Dr. Pankaj Kapupara, and Dr. Ketan Shah, Digital Pharmaceutical Marketing: A Review, Research Journal of pharmacy and technology 2016; 9(1):108-112.

4. Fredrik Kerval. Application Report on AN-100 crystal selection guide. Texas instruments. 2013.

5. Steven Bible. Crystal Oscillator Basics and Crystal Selection for rfPICTM and PICmicro Devices. Microchip Technology Inc, 2002.

6. PCB design considerations for KSZ8841/42 family of Ethernet controllers, AN-139 MICREL, Inc. Available from URL: http://www.siongboon.com/projects/2006-03-06_serial_communication/an-139%20%28how%20to%20route%20ethernet%20PCB%29.pdf

7. i.MX28 layout and design guidelines, AN4215- Free scale semiconductor, Document Number AN4215, 2010. Available from http://www.nxp.com/assets/ documents/data/en/application-notes/AN4215.pdf

8. Alexander Weiler and Alexander Pakost. High-speed layout guidelines, Texas Instrumensts, Tech. Rep., 2006. Available from URL: http://www.ti.com/ lit/an/scaa082/ scaa082.pdf.

9. Micron Application Note on Bypass capacitor selection for high speed designs. Available from URL: https://www.micron.com/~/media/documents/products/technical-note/tn0006.pdf.

10. Analog Devices report on Decoupling Techniques (MT101). Available from URL: ww.analog.com/ media/en/training-seminars/tutorials/MT-101.pdf

11. Shengyi technologies S1000 datasheet. Available from URL: https://www.multi-circuit-boards.eu/fileadmin/ pdf/leiterplatten_material/shengyi_s1000-2__www.multi-circuit-boards.eu.pdf

12. Hitachi MCL-E-679 Datasheet. Available from URL: http://www.hitachi-chem.co.jp/english/products/bm/b02/001.html

13. High-performance Laminates and Prepreg Materials. 370HR Datasheet –Isola. Available from URL: http:// www.isola-group.com/wp-content/uploads/2016/04/370HR-Laminate-and-Prepreg-Data-Sheet-Isola.pdf.

14. PCB Surface finishes – Advantages and disadvantages. Available from URL: http://www.epectec.com/ articles/ pcb-surface-finishadvantages-and-disadvantages.html.

Received on 15.04.2017 Modified on 28.09.2017

Research J. Pharm. and Tech 2017; 10(12): 4167-4171.

DOI: 10.5958/0974-360X.2017.00759.4