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Data transmission with gbits speed using cmos based integrated circu

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Data transmission with gbits speed using cmos based integrated circu

  1. 1. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976- 6367(Print), ISSN 0976 – 6375(Online) Volume 4, Issue 3, May – June (2013), © IAEME 188 DATA TRANSMISSION WITH GBITS SPEED USING CMOS BASED INTEGRATED CIRCUITS FOR OPTO-ELECTRONIC INTERFACES AND APPLICATIONS R. K. Singh, Ashish Dixit Department of Electronics & Comm. Engineering, Kumaon Engineering College (KEC), Dawarahat (Almora), Uttarakhand ABSTRACT The performance of the data transmission using the principle of the optical communication can be enhanced further simply by increasing both the wavelength count and bit rate per channel, so as to improve the utilization of the optical fiber bandwidth. This approach in turn requires the most suitable device structures and the technologies for both opto-electronic transducers and the associated driving electronics circuitry. The number of transistor stages required between the power and ground rails is only two so that the minimum supply voltage required is one threshold voltage plus one pinch-off voltage. The pre-amplifier is a balanced two-stage configuration such that the effect of bias-dependent mismatches is minimized. A new inductive series-peaking technique has been introduced so as to enhance the bandwidth by utilizing the resonance characteristics of LC networks. In addition to this arrangement, a new negative differential current feedback technique has been put forward for the discussion so as to boost the bandwidth of the system and to reduce the value of peaking inductors. This pre-amplifier circuit has been implemented in TSMC 0.18 µm, 1.8 V, 6-metal mixed mode CMOS technology and is analyzed using Spectre from Cadence Design Systems with BSIM3v3 device models. For an optical front-end with a 0.3 pF photodiode capacitance, simulation results demonstrate that the pre-amplifier has bandwidth of 3.5 GHz and provides a trans-impedance gain of 66 dB. The total chip area is approximately 1 mm2 and the DC power consumption is about 85 mW INTERNATIONAL JOURNAL OF COMPUTER ENGINEERING & TECHNOLOGY (IJCET) ISSN 0976 – 6367(Print) ISSN 0976 – 6375(Online) Volume 4, Issue 3, May-June (2013), pp. 188-203 © IAEME: www.iaeme.com/ijcet.asp Journal Impact Factor (2013): 6.1302 (Calculated by GISI) www.jifactor.com IJCET © I A E M E
  2. 2. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976- 6367(Print), ISSN 0976 – 6375(Online) Volume 4, Issue 3, May – June (2013), © IAEME 189 Keywords: Optical fiber transmission, Optoelectronic device, Integrated circuit, High rate, State of the art, Two-dimensional electron gas transistor, Gallium arsenide, Indium phosphide current-mode circuits, preamplifier, inductive peaking, current feedback I. INTRODUCTION The Optical communications is one of the corner stones of today’s revolution in the information technology. The vast distances of optical fiber span the globe, connecting the world together in an intricate communications infrastructure. With the drive towards portable and multimedia communications, the system has increasingly faced with the challenge of bringing the capacity of our communications infrastructure directly to the user, providing seamless access to vast quantities of information, any where and anytime. Whether it is the transfer of an image from a digital camera to a laptop computer or the communication of data within a massively parallel computer, there is an urgent need to develop new methods of high speed data communications. Light offers many advantages as a medium for communication. Whether travelling through free space or through optical fiber, light enjoys unequalled channel bandwidth, and is capable of data rates in the terabits per second. This immense capacity is due to the nature of the photons that constitute an optical signal. As such, the optical signals neither generate nor are sensitive to electromagnetic interference (EMI), parasitic coupling, and other problems faced by electrical. Given their advantages, optical links are rapidly expanding into application areas beyond traditional fiber-optic links. Three simple applications of so-called “carrier” applications that are concerned with transporting information across the greatest possible distance are free-space inter satellite links, fiber-to-the-home (FTTH) and terrestrial free-space links for inter-building [01-03]. The shorter distance applications include the optical-based local area networks (LANs) as represented by Asynchronous Transfer Mode Passive Optical Networks (ATMPON and Gigabit Ethernet standards based applications that involve the optical communications within digital systems or in large computers i.e. generally referred to as optical interconnect that include smart pixel arrays, opto-coupler arrays and optical backplanes [06]. In particular, the short-range “point-and-shoot” systems in accordance to the Infrared Data Association (IrDA) provide a simple solution for transferring information to and from portable devices, offering high data rates at low cost and with a small form factor that is not prone to mechanical wear. The success of such short-range systems is particularly telling of how optical communication systems are likely to proliferate in the future: as of 1998, over 100 million laptops, digital cameras, and other devices were shipped equipped with IrDA-compatible serial ports, and currently over 40 million new devices are being produced yearly. The IrDA wireless link has overshadowed both the Universal Serial Bus (USB) and IEEE 1394 FireWire to become the leading serial-port alternative for connectivity [04-07]. Figure 1.1 shows the basic elements of an optical link. On the transmit side, an information source produces a data stream that is encoded and sent to the appropriate drive circuitry used to modulate the optical signal generated by either a light emitting diode (LED) or laser. The signal propagates through free space or through a waveguide such as optical fiber until it reaches the photo detector on the receiver end. The photo detector converts the optical signal into an electric current that is sensed by the optical pre-amplifier and regenerated to a sufficiently strong voltage signal from which the original data can be recovered by the demodulator.
  3. 3. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976- 6367(Print), ISSN 0976 – 6375(Online) Volume 4, Issue 3, May – June (2013), © IAEME 190 Figure 1 Block diagram of a typical optical link. The expansion of optical communications into new applications has created exciting opportunities for the research and innovation of optical receivers. While the growth of fiber- optic networks in the last few decades has refined our understanding of optical receivers, its primary focus has been on speed and sensitivity. With the expansion of optical communications come new requirements on receiver designs. Probably the most widespread trend has been that of increased system integration and the drive to reduce system components, cost, and size. Traditionally, optical receivers have not been subject to many system level constraints since optical receivers for long-haul fiber-optic networks are principally designed for performance rather than cost. As such, they have typically used advanced high-speed semiconductor technologies such as GaAs and Si bipolar processes. Increasingly, the new optical receiver designs are being implemented in low-cost, high- integration technologies such as CMOS. However, the desire to implement in CMOS implies a need to design receivers that keep pace with developments in CMOS technology. One of the dominant trends is the continuous reduction of the system supply voltage as shown in Figure 1.2. The upper and lower boundary lines are drawn to highlight the fact that the ‘industry standard’ voltage is disappearing, being replaced instead by a range of voltages encompassing different applications. Increasingly, the supply voltage is seen as an adaptable design parameter used to optimize performance and minimize power. The logic circuits that operate with supply voltages near or even below the threshold voltage are being reported alongside analog circuits that do the same. The low-voltage operation is partly driven by the desire for low power in portable applications and in applications that require battery back-up such as fiber-to-the-home (FTTH). In the end, low-voltage operation will be crucial to the long-term viability of integrated optical receivers [08-10]. Figure 2 Projected trends in system supply voltages. The recent advance in CMOS technology, mainly driven by the low-power applications, has significantly lowered supply voltage. The reduction in threshold voltages, however, is rather moderate in order to minimize the static power consumption arising from
  4. 4. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976- 6367(Print), ISSN 0976 – 6375(Online) Volume 4, Issue 3, May – June (2013), © IAEME 191 sub-threshold conduction. As a result, the performance of voltage mode circuits, such as dynamic range, is affected greatly. CMOS current-mode circuits offer many attractive advantages over their voltage-mode counterparts. The key performance feature of current- mode circuits is their inherent wide bandwidth. The other advantages include low supply voltage requirement, large dynamic range, and tunable input impedance. These characteristics make current-mode circuits particularly attractive for high-speed interface circuitry. The analog amplifiers are susceptible to power and ground fluctuations caused by the switching of digital portion of mixed-signal circuits, such as clock and data recovery circuits in optical transceivers. The accuracy of current-mode circuits is severely affected by the errors due to device mismatches. Low-voltage current-mode circuits that are insensitive to device mismatches and switching noise are highly desirable. In addition, a main drawback of current- mode circuits is their low current gain. To increase the current gain, the size of the transistor in the output branch can be made large, how-ever, at the cost of reduced bandwidth. The technique introduced increases the bandwidth of current-mirror amplifiers by cancelling out the dominant pole with a compensating zero obtained by inserting a resistor between the gates of the input and output transistors of the amplifiers. In this system, an adjustable gain optical amplifier is used in front of the photo receiver, so as to reduce both the requirement in receiver sensitivity and the amount of gain required from the electronic amplifier. A flip-flop is then used so as to perform the decision making part. In the present scenario, the decision is usually not performed at the Gbit/s signal level because of the very limited availability of circuits clocked at GHz range. The signal transmission over the fiber suffers from a number of impairments such as chromatic dispersion enhanced by the chirp characteristics of the source, polarization mode dispersion, nonlinear channel interaction. Such impairments are getting more and more detrimental as the bit rate increases, most often they can be compensated at the optical signal power level or electronically at the receiver level [10-12]. The detailed schematic of the transmitter and receiver has been shown in figures 3 and 4 respectively. Figure 3 Schematic diagram of a Transmitter Figure 4 Schematic diagram of a Receiver II. REQUIREMENTS FOR THE GBIT/S OPTOELECTRONIC INTERFACE ICS As discussed in the introduction of the problem, both the analog (e.g. amplifiers) and digital ICs (e.g. MUXES) are needed for assembling the design of the optoelectronic transmitters and receivers, calling for specific requirements in terms of microelectronic
  5. 5. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976- 6367(Print), ISSN 0976 – 6375(Online) Volume 4, Issue 3, May – June (2013), © IAEME 192 technology characteristics. For the analog parts, what matters first is the gain available over the required bandwidth from a given technology; much attention is then paid to the power gain cut-off frequency FMAX, known as the maximum oscillation frequency i.e. higher the FMA X, higher the available gain over a given, large, bandwidth. For the bandwidths required at a specific data transmission rate in Gbit/s range depending on the application requirements, only the technologies offering FMAX can be envisioned. For example, For a given technology, the distributed amplifier structures help getting the better in terms of gain-bandwidth product: actually, assuming identical impedance for both input and output lines and loss-less lines, the total voltage gain (Gv) is set by both the stage (transistor) gain (Gs) with Gs = gm Z, where gm is the transistor trans-impedance, and the number of stages (N); a situation to be contrasted with conventional lumped amplifiers [13]: Gv ≈ Gs × N/2 (distributed amplifier) (1) Gv ≈ GsN (lumped amplifier) (2) These above mathematical expressions indicate that even with a stage gain close to one, that is with a stage bandwidth close to FT, a large total gain can be obtained with distributed amplification (although limited by the line losses which set a limit to the bandwidth as well as to the number of stages), while the lumped amplifier requires the stage gain to be sensitively larger than one to provide a large total gain. Figure 5 Gain vs. bandwidth characteristics of single chip amplifiers. Thus, based on the discussion to a larger extent, the performance of the interconnection depends on the receiver’s gain, bandwidth, power consumption, and area requirements. These four parameters can be traded off against each other. By adjusting the number of amplifying stages, the transistor sizes, and the bias voltages, the receiver circuit can be designed to optimize the link performance i.e. 1) Bit Rate: The location of the poles in the receiver transfer function determines the 10– 90% rise time in response o a step input. The bit rate of the overall receiver can be determined from the rise times of each of the components BR [14] (3) where ζ determines what percentage of the bit period makes up he rise time. The rise times for the receiver components are given in Table I. The TIA is designed to have a response that closely approximates a maximally flat magnitude (MFM) response, i.e. the two poles closest to
  6. 6. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976- 6367(Print), ISSN 0976 – 6375(Online) Volume 4, Issue 3, May – June (2013), © IAEME 193 the origin are at 45. This is achieved with an appropriate value feedback resistor. It can be seen from Table I that receivers with a three-stage TIA are significantly slower than ones with a one-stage TIA, when both are constructed from identical amplifying stages. In general, it can be shown that when the number of stages in a feedback loop increases, the bandwidth decreases. However, in order to determine when three-stage TIA based receivers are competitive, the trans-impedance gain must be examined as well [15]. Table 1 10–90% rise time formulas 2) Transimpedance Gain: The trans-impedance of the receiver determines its sensitivity. In order to ensure stability and eliminate resonance peaking in the receiver transfer function, the trans-impedance of the amplifier is adjusted to approximate a maximally flat magnitude response. The trans-impedance can then be calculated based on the gain, bandwidth, input capacitance and transconductance of the amplifying stages, the total number of stages, and the photodiode capacitance. For the one-stage TIA to have a maximally flat magnitude response, the input open-loop pole must be smaller than the second open-loop pole by a ratio of [16] (4) Cpd is the photodiode capacitance plus any parasitic capacitance, and is taken as 100 fF in the analysis. This corresponds to a flip-chip bonded 400 m MQW detector. Since optical alignment and spot sizes are not expected to scale as the gate length of the technology, this value is constant for all three technologies considered in this paper. The value of Rf obtained by solving (2) is used to determine the trans-impedance of the one-stage TIA, which is given by [17] (5) The three-stage TIA has four open-loop poles, one at fin and three overlapping poles at fout. In order for the three-stage TIA to approximate a maximally-flat magnitude transfer function, the input open-loop pole must be related to the other three open-loop poles by [18] (6)
  7. 7. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976- 6367(Print), ISSN 0976 – 6375(Online) Volume 4, Issue 3, May – June (2013), © IAEME 194 The trans-impedance of the three-stage TIA is given by equation 6, with 1+ Av -1 replaced with 1+ Av -3 , since there are now 3 stages providing gain in the TIA. The overall trans-impedance gain, TZ, is the receiver’s output voltage divided by the input current, and is given by the voltage gain of the -stage post amplifier times the trans-impedance of the TIA [19] (7) 3) Noise: The circuit noise introduced by the receiver and detector is referred to the receiver input for signal to noise ratio determination. 4) Power: The electrical power dissipation of the (N+P) stage receiver is determined from the bias current Ids, and the power supply voltage Vdd, and can be written: (8) There is additional power dissipation due to the switching of the node capacitances in the receiver, but this component is orders of magnitude less than the power dissipation due to the bias current [20]. The low frequency noise is another feature of importance, as it impacts the spectral purity of oscillators and multipliers (the jitter tolerances are quite stringent for the various circuits, as the peak to peak jitter should be lower than 2 ps). Digital lCs operating in the range of Gbit/s are often thought of as mixed-signal lCs as their microwave/analog features have a major impact on their digital operation. When considering a basic assembly of logic gates, the operating speed is often quoted through the gate propagation delay time (xr, o), which depends on both the switching transistor intrinsic speed and the response time of the surrounding circuit, as shown in the following expression: TpD = (2riFT)-1 + n(Cp +CI) AV/I (9) where n is the gate fan-out (usually small in very high-speed ICs), C~ and Cp stand for the input capacitance of a gate and the parasitic (wiring) capacitance respectively; AV and I are the voltage swing and the active load current respectively. To keep with general statements, one could point out the following requirements [21-25]: • high current density, so as to reduce CIfI: this obviously implies small dimension transistors in order to avoid thermal problems, as well as a high current density; • low wiring capacitance: this calls for a compact layout, and thick enough dielectric layers to reduce interconnection capacitance. This is especially important for FET technologies as they are usually characterized by lower C I (and lower currents) than bipolar processes as shown in figure 6.
  8. 8. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976- 6367(Print), ISSN 0976 – 6375(Online) Volume 4, Issue 3, May – June (2013), © IAEME 195 Figure 6 Digital circuits speed vs. device performance, III. CURRENT STATUS OF III-V ELECTRONIC TECHNOLOGIES FOR 40 GBIT/S ICS The semiconductor technologies considered presently for the fabrication of 40 Gbit/s ICs include SiGe bipolars, GaAs pseudomorphic and metamorphic HEMTS and HBTS (Heterojunction Bipolar Transistors), InP HEMTS and HBTS. Together these technologies have already produced los able to allow the demonstration of first generation 40 Gbit/s systems, even though further developments are obviously needed to obtain chip sets able to fit the requirements of commercial optical systems. These various technologies keep evolving and make continuous progress in terms of high-speed performance, consumption and/or cost. As an example, during the last 10 years, the speed of static frequency dividers has been improved by a factor of 2.5 to 5 for the InP and SiGe bipolar technologies respectively [26]. With this evolution in mind, one can also envision Si CMOS to be finding applications in a 40 Gbit/s chip set, in particular as transmission impairments mitigation will require rather complex circuits. Shrinking the gate length below 100 nm, introduction of SiGe p-MOSFET structure and other developments presently in progress may bring new openings for CMOS in 40 Gbit/s applications [27]. The main factors that will decide which technologies will be chosen are probably the following, their respective weight depending on the application: • Performance i.e. the key factor even though the specifications are not yet fully defined and some margin will be appreciated to overcome dispersion, aging, characteristics degradation after packaging, • Target specifications i.e. as the optoelectronic components or even the transmission fiber characteristics evolve, specifications may change, making it more appropriate to use another technology for a given function. • DC power consumption i.e. as the wavelength-multiplexing capability is a system requirement, low consumption is an important factor to reduce footprint of terminal equipments. A total power consumption of 10-12 W is presently targeted for a transmitter-receiver pair. • Gate count is another important aspect, since signal processing is becoming most useful (FEE, impairment mitigation) as bit rate increases. • Cost is obviously an issue and this applies to the complete transponder.
  9. 9. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976- 6367(Print), ISSN 0976 – 6375(Online) Volume 4, Issue 3, May – June (2013), © IAEME 196 TABLE 2: Figure of merit for various materials [28] III.1. GaAs ICs for 40 Gbit/s applications: The GaAs microelectronics device has long been a choice of the technology for the design of high-speed circuits for optical transmission, in particular with MESFETS used as photo receiver preamplifiers and in digital ICs. As bit rates kept increasing, the MESFET technology ran out of performance, leaving the field to hetero-junction technologies that are now exclusively used in 40 Gbit/s high-speed interfaces [29]. IILI.1. GaAs HEMTS and 40 Gbit/s analog circuits: Since the GaAs HEMT was invented in 1980, many improvements have been brought to the structure, in particular with the introduction of the so-called k-doping of the barrier layer and the pseudomorphic strained InxGal_xAS channel, with an In content of x = 0.25. This pseudomorphic channel is characterized by a smaller band gap than GaAs, which increases the conduction band discontinuity with the barrier (hence a higher electron sheet density in the channel), and higher electron mobility than GaAs as shown in figure 7. These characteristics translate into a higher current density, hence larger FT and FMAX, while retaining very attractive break- down behavior [30]. However, this is not possible since the critical strained channel thickness beyond which dislocations appear would become too small to accommodate a large enough carriers density. To overcome this limit, a new concept was introduced with the metamorphic HEMT (M-HEMT) characterized by an InGaAs channel with a much higher In content (usually 0.3 <x< 0.5). The InGaAs channel and its lattice- matched AllnAs barrier are grown on a strain-relaxed thick buffer that accommodates the lattice mismatch and absorbs dislocations originating from the GaAs substrate. Figure 7 GaAs P-HEMT and InP composite channel HEMT structures [31]
  10. 10. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976- 6367(Print), ISSN 0976 – 6375(Online) Volume 4, Issue 3, May – June (2013), © IAEME 197 IIl.l.2. GaAs HBTS and mixed signal circuits: The potential of GaAs HBTS for the fabrication of optical telecommunications ICS has also been explored. Worth noting is the successful development of a 10 Gbit/s chip set by Nortel some years ago [32]. Pushing further this technology towards 40 Gbit/s applications has been an objective for a few research domains, and 20 Gbit/s-class digital circuits have been also produced to some extent [34-35]. More recently, using a highly doped re-grown extrinsic base structure, which helps reducing the access base resistance and allows high FMA X (close to 200 GHz for an F T above 100 GHz), the research demonstrated a 43 Gbit/s receiver chip set including a decision circuit [36]. However, the most developments in GaAs HBT technology are focused on microwaves applications, such as power amplifiers for hand sets, with little development effort left for adjusting to the requirements of very high bit rate circuits i.e. reducing the emitter width and the base-collector junction area to improve cut-off frequencies, demonstrating a new base material to lower the turn-on voltage and reduce the power consumption [37]. III.2. 40 Gbit/s ICs on InP substrates: InP and its related compounds, AlInAs and InGaAs, have produced transistors with record high frequency performances for quite a few years; with the projected development of optical transmission at 40 Gbit/s, first commercial microelectronics applications have been envisioned for those materials, in spite of both the brittle substrates making processing more difficult than with GaAs wafers and the limited substrate size (3 to 4 inch semi-insulating wafers are presently used; but one should notice that some 3-4 inches GaAs foundries are still profitable) [38]. However, the broad variety of available hetero structures in the InP family offers the device designer a full range of combinations to optimize HEMTS and HBTS, in terms of high-speed and high-output voltage [39]. III.2.1. InP-based HEMT circuits: A record cut-off frequencies have been reported since the early 90s for InGaAs- channel InP-based HEMTS, with values of 350 GHz for F T and 600 GHz for FMA x for 0.1 lain gate length, recently increasing to 560 GHz for F T at 25 nm gate length [40]. These figures actually translate the high electron saturation velocity in InGaAs and the high confinement energy of the InA1As/InGaAs hetero junction (about 0.5 eV). Such high frequency performances have led to record high bit rate operation of digital ICs, such as MUXes, DMUXeS and decision circuits, and a complete 40 Gbit/s AllnAs/GaInAs HEMT chip set a few years ago [41]. The first and foremost circuits have been fabricated, including arrays of monolithically integrated photodiode/preamplifiers (designed for 10 Gbit/s applications and wide-band (90 GHz) distributed amplifiers as shown in figure 8, characterized by a state of the art 410 GHz gain-bandwidth product and a promising output swing of 2 V [42-45].
  11. 11. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976- 6367(Print), ISSN 0976 – 6375(Online) Volume 4, Issue 3, May – June (2013), © IAEME 198 Figure 8 InP composite channel HEMT 10 stage distributed amplifier [46] III.2.2. InP-based HBT circuits: An InP-based HBT static frequency divider operating at 39 GHz has been discussed quite earlier. However, it is only in recent years that the InP-based HST technology was identified as a choice technology for assembling a 40 Gbit/s digital chip set. The HST technology can be considered as a maturing technology and different InP structures and processes are still investigated worldwide: single or double hetero structure (D-HBT), AlInAs or InP emitter, InGaAs or GaAsSb base, Zn, Be or C doping of the base, now taking advantage of both of the selective etching properties of the emitter-base and base- collector hetero junctions, and the low recombination velocity of InGaAs (or GaAsSb) surface, small dimension HBTS (emitter width below 1 lam) can be processed, as needed for high frequency / low power consumption performances [47]. Figure 9 Schematic band diagrams of lnP D-HBT structures In the InP HBT technology, this is competing with the SiGe one i.e. MUX and DMUX ICs have also been developed in the later technology, as well as wide band amplifiers, and further improvements with the performances are likely to result from continuous progress in cut-off frequencies (an F T > 200 GHz has recently been reported at an emitter width of 0.12 ~tm. The static frequency dividers operating above 80 GHz have been discussed, at a frequency close to the best InP. However, very thin collectors are required to produce such fast devices, which sets a limit to the output voltage they can sustain. The InP D-HBT process developed at or, to+ is based on a structure with a graded base grown by using the chemical beam epitaxial approach [48-52].
  12. 12. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976- 6367(Print), ISSN 0976 – 6375(Online) Volume 4, Issue 3, May – June (2013), © IAEME 199 Figure 10 Evolution of InP HBTS cut-off frequencies with emitter width [53] A mixed dry and wet chemical etching allows for an undercut collector, which is instrumental in reducing the base-collector capacitance and reaching high cut-off frequencies (F T = 180 GHz; FMA x = 220 GHz), suitable for designing 40 Gbit/s ICS. A number of 40 GbitJs-class circuits, such as a 2.2 V selector-driver and more recently a family of D Flip-Flops aimed at 3R regeneration or Decision characterized by a high sensitivity, a large phase margin and a low jitter well below 1 ps as shown in figure 11 [54]. Figure 11 Eye diagrams illustrating the regenerating characteristics of InP D-HBT flip-flops [55] CONCLUSION With the first 10 Gbit/s WDM systems now in full operation, the focus of the research laboratories has now shifting towards more efficient systems with denser wavelength multiplex or higher bit rate. The transmission of the data at a rate of 40 Gbit/s per channel has motivated the development of new components for dispersion management, faster optoelectronic devices and lCs enable to operate at such high bit rate. In the last few years, ICs were reported in various technologies, able to operate at the proper speed, then offering the required functionality with the possible further improvement needed in terms of power consumption, most circuits needed for the fabrication of transmitters and receivers operating at 40 (or 43 Gbit/s). Large signal models able to describe accurately the operation of active devices and specific circuit design tools and methodologies which have been purposely developed also contributed largely to the demonstration of circuits suitable to 40 Gbit/s transmission, that is offering some speed margin with respect to system specifications. Now in order to make 40 Gbit/s transmission a reality, it is mandatory to demonstrate its cost effectiveness, which applies to the cost of both transmission and terminal equipments. For that reason, it is still questionable to identify short reach or long haul transmission as the first market for 40 Gbit/s transmissions.
  13. 13. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976- 6367(Print), ISSN 0976 – 6375(Online) Volume 4, Issue 3, May – June (2013), © IAEME 200 ACKNOWLEDGEMENTS The authors are thankful to Prof. D. S. Chauhan (Vice Chancellor, UTU) for providing the environment for this work, Mr. Aseem Chauhan (Additional President, RBEF), Major General K. K. Ohri, AVSM, Retd. (Pro VC, AUUP, Lucknow Campus), Prof. S. T. H. Abidi (Director, ASET) and Brig. Umesh K. Chopra, Retd. (Dy. Director, ASET) for their kind cooperation, motivation, kind and most valuable suggestions. REFERENCES [1] Sitch (j.) Integrated circuits for fiber systems, (2002) digest of ieee gaas ic symposium, pp. 19-22. [2] Tsai (h.s.), kopf (r.), melendes (r.), melendes (m.), tate (a.), ryan (r.), hamm (r.), chen (y.k.) 90 ghz baseband lumped amplifier, (20001, electron. Let., 36, pp. 1833- 1834. [3] Wooten (e.l.), kissa (k.m.), yi-yan (a.), murphy (e.j.), lafaw (d.a.), halemeier (p.e), maack (d.), atranaslo (d.v.), fritz (d.j.) mcbrien (g.j.), bosst (d.e.), a review of lithium niobate modulators for fiber-optic communications systems, (2000), ieee journal selec.topics quant. Electron., 6, pp. 69-82. [4] Scavennec (a.), giraudet (l.) Optical photodetectors, in fiber optic communication devices, springer 2001, editors norbert grote, herbert venghaus. [5] Green (m.m.), momtaz (a.), vakilian (k.), wang (x.), jen (h-c.), chung (d.), cao (j.), carerosa (m.), hairapetian (a.), fujimori (1.), car (y.) Oc-192 transmitter in standard 0.18/am cmos, (20021, techn. Digest teee tsscc, 1, pp. 248-249. [6] Razavi (b.) Prospects of cmos technology tot high-speed optical communication circuits, (2002), ieee journ. Solid-state circuits, 37, pp. 1135-1145. [7] Johnson (e.o.) physical limitati•ns on frequency and power parameters of transistors, ( 1965)• rca review, 26, pp. 163-177. [8] Delage (s.) Heterojunction bipolar transistors for millimeter-wave applications : trends and achievements, (2001), annales tall(com., 56, n ° 1-2, pp. 5-14. [9] Bollaert (s.), cordier (y.), zaknoune (m.), parenty (t.), happy (h.), cappy (a.), hemt's capability tbr millimeter-waves applications, (2001), annales tdldcom., 56, n ° 1-2, pp. 15-26. [10] Virk (r.s.], camargo (e.), hajji (r.), parker (s.), benelbar (r.), notomi (s.), ohnishi (h.) 40-ghz mmics for optical modulator driver applications, (2002), teee mtr- symposium, pp. 91-94. [11] Yuen (c.), laursen (k.), chu (d.), mar (k.), 50 ghz high output voltage distributed amplifiers for 40 gbit/s eo modulator driver application, (20(/2), teee mrr-symposium, pp. 481-484. [12] Lefevre (r.), mouzzanar (w.), lestra (a.), vuye (8.), ferling (d.), jorge (f.), pillet (o.), idler (w.), double distributed gaas p-hemt ics lor 40 gbit/s high output voltage driver modules, (2001), techn. Digest gaas mantech, pp. 134-136. [13] Nowotny (u.), lao (z.), thiede (a.), lienrlart (h.),hornung(j.), kaufel (g.), kohler (k.), glorer (k.), 44 gbit/s 4:1 multiplexer and 50 gbit/s multiplexer in pseudomorphic a1gaas/gaas hemt technology, (1998) ieee tscas, technical dig. Ii, pp. 201-203.
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