Course Title: High-Speed Wire line/optical Transceiver Design

Transcription

1 Course Title: High-Speed Wire line/optical Transceiver Design Course Outline Introduction to Serial Communications Wire line Transceivers Transmitters Receivers Optical Transceivers Transimpedance Amplifiers (TIAs) Limiting Amplifiers Jitter in Serial Communication Phase lock loops Clock and data recovery Green Electronics Environmental Progress in Green Electronics Reliability of GE, Fabrication of Green PCBs & Green IC Finishes Cairo University Transceiver Design M. Youssef 2

2 Course Main Textbooks/References Design of Integrated Circuits for Optical Communications, by Behzad Razavi Broadband Circuits for Optical Fiber Communication, by Eduard Sackinger Green Electronics, Design & Manufacturing, by Sammy G. Shina Cairo University Transceiver Design M. Youssef 3 Integrated Circuit Design Cycle Design can take place in small size startups with no fabrication facilities Startups seek seed money from VCs for exchange of some company equity Startups provide a very high risk/high profit margin investment opportunity for VCs Integrated Device Manufacturors (IDMs) have their own fab. facilities such as: Intel, Samsung, Toshiba, TI, Fabless Semiconductor companies can use any of the dedicated foundries to fabricate their products The biggest semiconductor foundries according to their revenue are: TSMC in Taiwan, UMC in Singapore, IBM & TowerJazz in the US, TSMC offers a wide range of CMOS technologies such as:.13um, 9nm, 65nm, 55nm, 4nm, 28nm, IBM and TowerJazz offer HBT BiCMOS processes geared more towards high frequency RF ICs Cairo University Transceiver Design M. Youssef 4

3 Integrated Circuit Design Cycle (Cont d) Dicing & Packaging Left: Picture of a 2-inch (51 mm), 4-inch (1 mm), 6-inch (15 mm), and 8-inch (2 mm) wafers Currently most foundries support 12-inch wafers Dicing & Packaging could be done at specialized packaging houses Now your product is ready to be tested, and upon success released to the market Cairo University Transceiver Design M. Youssef 5 Wireless vs. Wire Line Communication Wire line/optical transceivers deal with much wider band signals compared to RF transceivers Wide band signals require wide band circuits for wire line/optical transceiver front-ends Cairo University Transceiver Design M. Youssef 6

4 Wireless vs. Wire Line Communication Typical Parameter Data rates BER Received signal levels Main stream applications Wire line/ Optical 1-1Gbps 1-12 to mv Data transmission, storage, networks, long haul communication Wireless 384Kbps - 672Mbps* 1-4 to dBm (1uV) Voice, low data rate data/video transmission * Although wireless data rates are low high carrier frequencies might be utilized, up to 6GHz Cairo University Transceiver Design M. Youssef 7 Lecture 1: Introduction to Serial Communication

5 Lecture 1: Outline Introduction to serial standards Transmission Medium Digital Modulation Line coding Properties of Binary NRZ Random Data Pseudo Random Binary Sequences Cairo University Transceiver Design M. Youssef 9 Introduction High-speed serial transceivers offer a cheaper alternative compared to parallel interfaces having the same throughput by reducing the number of I/Os and PCB traces Clock skew becomes unavoidable in high-speed serial link necessitating special circuitry for clock recovery at the receiver Similarly for optical communication the huge bandwidth offered by fiber has allowed multiplexing more than one parallel data streams to transmit them onto one fiber channel Serial standards serve a variety of different applications: Local/wide area networks, computer busses, portable devices, storage devices, peripheral devices, MAC to PHY links, and digital video interconnects Wire line applications Optical applications Cairo University Transceiver Design M. Youssef 1

6 Serial Standards Overview Wire line standards: 1G Ethernet: 1Gbps computer networks CEI-6G, CEI-11G, CEI-28G: 6,11, and 28 Gbps interfaces for application in high-speed backplanes, chip-to-chip interconnects, and optical modules USB: 48Mbps, 5Gbps communication and power supply between computers and electronic devices Gigabit Ethernet: 1Gbps local area networks PCI Express 2.5, 5, 8Gbps: a computer expansion card standard designed to replace the older PCI, PCI-X, and AGP bus standards SATA (Serial Advanced Technology Attachment) 1.5, 3, and 6Gbps: a computer bus interface for connecting host bus adapters to mass storage devices such as hard disk drives and optical drives SAS (Serial Attached SCSI): a computer bus standard used to move data to and from computer storage devices such as hard drives and tape drives. SAS replaces the old parallel SCSI bus technology XAUI: a standard for extending the XGMII (1 Gigabit Media Independent Interface) between the MAC and PHY layer of 1 Gigabit Ethernet (1GbE) Optical Standards: SONET (Synchronous optical networking): OC Gbps, OC-192 1Gbps, OC-768 4Gbps standardized multiplexing protocol that transfer multiple digital bit streams over optical fiber using lasers or (LEDs) GPON (Gigabit capable passive optical network): 2.5Gbps, 1Gbps (1G-PON) a point-tomultipoint, fiber to the premises network architecture in which optical splitters are used to enable a single optical fiber to serve multiple premises Fibre Channel: 1-2GFC storage area networks over fiber optic cables or twisted pair copper wires Cairo University Transceiver Design M. Youssef 11 1Gigabit Ethernet Router with 1G Ethernet ports use 1G SFP/SFP+ (small form-factor pluggable) modules to interfaced to fiber optic cables SFP+ modules can retime the data and re-transmit it through PCB traces/connectors to the SerDes (SerDes Framer Interface: SFI interface) Cairo University Transceiver Design M. Youssef 12

7 Physical Layers (PHYs) for Serial Standards The PHY is the first and lowest layer in the seven-layer OSI (Open Systems Interconnection) model of computer networking, responsible for: Providing a standardized interface to physical transmission media, including Mechanical specification of electrical connectors and cables, for example maximum cable length Electrical specification of transmission line signal level and impedance Digital Modulation and Line coding Equalization Forward error correction Cairo University Transceiver Design M. Youssef 13 Transmission Medium Types of transmission medium (channel): Electrical Medium: Twisted pair cables Co-axial cables Chip-to-chip PCB traces Backplanes Optical Medium: Fiber channel Electrical channel Non-idealities Insertion loss (signal attenuation) Return loss (channel impedance and reflections) Noise & crosstalk Optical channel Non-idealities: Modal, chromatic, and polarization mode dispersion Nonlinearities Cairo University Transceiver Design M. Youssef 14

8 Digital Modulation The most common modulation technique used in serial links is OOK (on off keying), i.e. the signal is on to transmit a one and off to transmit a zero, this is also termed NRZ (non-return to zero) Other common modulation techniques: RZ (return to zero), and Manchester NRZ is the most commonly used line code by serial standards due to it s simplicity and it requires less channel bandwidth, RZ includes a spectral line at a frequency equal to the bit rate which facilitates clock recovery. However the receiver and transmitter need to process shorter pulses Digital signal V s NRZ signal -V s +V s RZ signal -V s Cairo University Transceiver Design M. Youssef 15 Digital Modulation (Cont d) Multi-level signaling uses more signal levels to represent the digital bits being transmitted to reduce the channel bandwidth requirements Most serial standards such as PCIe, SATA, SAS, SONET, require binary signaling Some Ethernet standards requires multi-level signaling For example, a 4-PAM (pulse amplitude modulation) signal represents each two consecutive bits by one symbol which is allowed to take one of 4 voltage levels Digital signal V s Binary NRZ signaling -V s Multi-level signaling: 4-PAM signal -V s +Vs /3 Cairo University Transceiver Design M. Youssef 16 +V s -V s /3

9 Line coding The presence of long runs of 1s or s, i.e. long CIDs (consecutive identical digits) in the data stream creates problems for clock recovery circuits Also having unequal number of 1s or s on the long-term (i.e. non DC balanced signals) can create difficulties for the receiver So before bits are transmitted they are pre-conditioned using one or both of the following line coding techniques Block coding: To overcome this line coding techniques have been used, such as: 8b/1b, 64b/66b, 128b/13b encoding For example 8b/1b is a line code that maps 8-bit symbols to 1-bit symbols to achieve: difference between the count of 1s and s in a string of at least 2 bits is no more than 2 (DC-balance) not more than five 1s or s in a row (increase transition density) 8b/1b encoding represents a 25% reduction in throughput 128b/13b and 64b/66b are more efficient than 8b/1b in terms of throughput but allow longer CIDs Scrambling: Data from a pseudo random sequence generator is Xored with the transmitted bits The same procedure is used at the receiver to de-scramble the signal given that the same sequence is used Cairo University Transceiver Design M. Youssef 17 Properties of Binary NRZ Random Data The Binary NRZ signal can be represented by: x( t) = ak p( t ktb ) k where a k is ±1 and represents the transmitted symbols, p(t) is a rectangular pulse shape, T b is the bit duration The power spectral density S x (f) of x(t) has a sinc 2 shape and is given by: S x sin( πft ) b ( f ) = Tb πftb 2 Cairo University Transceiver Design M. Youssef 18

10 Properties of Binary NRZ Random Data (Cont d) Spectrum doesn t include any spectral lines to facilitate clock recovery For the 1Gbps example shown above, the majority of the signal power is concentrated between DC and 5GHz (1/2T b, Tb=1ps) i.e. the Nyquist frequency Cairo University Transceiver Design M. Youssef 19 Pseudo Random Binary Sequences During simulation & lab characterization of PHYs it is typical to use a known PRBS length (psuedo random binary sequence) for example PRBS 7, 15, or 31 PRBS sequences are generated using LFSRs (linear feedback shift registers) which try to emulate random signals. The feedback taps of an n-bit LFSR are chosen for the output sequence to appear random and only start repeating after 2 n -1 bits The longer the prbs order the more it s spectrum would like that of a real random signal given shown in the previous slides For example, the feedback polynomial for prbs7 is x 7 +x 6 +1 o/p D Q D Q D Q D Q D Q D Q D Q clk Cairo University Transceiver Design M. Youssef 2

11 Pseudo Random Binary Sequences (Cont d) Problem: Obtain the first 1 bits of prbs4 given that the polynomial for prbs4 is x 4 +x 3 +1 Current state Next state o/p o/p D Q D Q D Q D Q clk Cairo University Transceiver Design M. Youssef 21