A Fully Integrated 20 Gb/s Optoelectronic Transceiver Implemented in a Standard 0.13 µm CMOS SOI Technology School of Electrical and Electronic Engineering Yonsei University 이슬아
1. Introduction 2. Architecture 3. System Building Blocks A. Optical Components : Holographic Lens, Optical Waveguide B. Optoelectric Components : High Speed Mach Zehnder Modulator, Thermal Phase Modulator, Variable Optical Attenuator C. Electronic Components : Optical transmitter, Optical Receiver, Common Clock and Data Recovery Circuit 4. Experimental Results 5. Conclusion
Introduction <Conventional system> Optical data transceivers operating at 10 Gb/s have been implemented in CMOS but a low level of optoelectronic integration Conventional processes results in very high cost, dominated by the packaging and testing of different optical components. <Conventional multi wavelength optical communication system> This paper focuses on an application of the same technology to creating highlyintegrated communication systems. It describes the architecture, key building blocks, implementation and testing of a dual channel, 10 Gb/s per channel, C band (1550 nm) optoelectronic transceiver integrated in a SOI material system.
Architecture <Dual channel 10 Gb/s per channel optoelectronic transceiver architecthure> Two parallel high speed optoelectronic transceivers 10 Gb/s Transmit (TX) path : electrical input optical out put TX equalizer : compensate for a moderate amount of high frequency attenuation due to the electrical channel prior to the TX input Clock and data recovery (CDR) : retimed to remove jitter, create a clean, high amplitude signal Modulator driver (MD) : amplifies the signal to provide a high voltage Mach Zehnder Interferometer (MZI) : fourport network Input : a continuous wave (CW) optical signal with λ = 1.55 μm, and high speed electrical data Output : modulated optical signal and its complement
Architecture <Dual channel 10 Gb/s per channel optoelectronic transceiver architecthure> The input and output of the MZI is coupled in and out of the chip by holographic lens (HL). HL : couple normally incident light in and out of the silicon chip. commercially available High speed p i n photodetector (PD) Transimpedance amplifier (TIA) and limiting amplifier (LA) : amplify the received signal to levels that are compatible with the receive (RX) CDR circuit Variable optical attenuator (VOA) loopback Self testing of the complete optoelectronic TX/RX chain Feasibility of this technology in the implementation of intra chip interconnect 16 bit bus controller unit (BCU) : enables design for testability (DFT) as a critical function for managing the complexity of an integrated optoelectronic system.
System Building blocks Optical components An optical waveguide together with a transistor in the active layer of the CMOS SOI photonic technology Co existence of electronic and photonic devices in the same silicon layer allows photonic and electronic functions. <Conceptual cross section of a CMOS photonic technology > A. Optical Components 1) Holographic Lens (HL) Overcome a severe mode mismatch and high insertion loss for simple edge or end fire coupling Trench periodicity : optical phase matching, scatter light from an normally incident optical fiber into the silicon wave guide 2) Optical Waveguide It is etched into the active top silicon of SOI 0.5 μm wide <Holographic lens>
System Building blocks Optoelectronic components B. Optoelectronic Components 1) High Speed Mach Zehnder Modulator (Majority carrier Device) To impose high speed electronic data on the optical carrier wave Electric field change of carrier density phase shi construc vely/destruc vely interfere Reverse biased diode majority carriers to drift in and out of the optical mode : high speed 2) Thermal Phase Modulator, TPM (Thermo Optic Device) To use as phase tuners A resistor implanted in an op cal waveguide current flows heat up the waveguide index change phase change 250 µm long, 10 µm wide
System Building blocks Optoelectronic components 3) Variable Optical Attenuator (Minority Carrier Device) To impart an electrically controlled attenuation to an optical wave 1 mm long, 1 μm wide It consists of a lateral p i n diode integrated into an optical waveguide Forward biasing the diode causes carriers to accumulate in the intrinsic region carrier density change op cal absorption coefficient change An optical attenuation of up to 40 db may be induced with ~100 ma of applied current.
System Building blocks Electronic Components C. Electronic Components 1) Optical Transmitter The optical transmitter consists of a modulator driver circuit connected to the MZI. Optical modulating elements : reverse biased p n junction straddling a section of a waveguide Dual termination : avoid inter symbol interference (ISI) in the optical output due to signal reflections Modulator driver 4 bit word Current mode Logic (CML) Compensation of phase offset Large voltage can severely stress the breakdown limits M 1 with a pair of M 2 to protect the switching transistors from over voltage conditions
System Building blocks Electronic Components 2) Optical Receiver Consists of an external high speed p i n PD and a capacitance of 150fF that is connected to a TIA and followed by a five stage limiting amplifier (LA). Compares the received signal High gain average power against a locally created reference Feedback resistance to isolate Extending TIA bandwidth To reduce nose and provide stabilized gain
System Building blocks Electronic Components 3) Common Clock and Data Recovery Circuit Consists of a data recovery loop and a frequency acquisition loop Intrinsic data retiming phase locked loop (PLL)
Experimental Results <Chip microphotograph> <Packaged dual channel transceiver system> System chip with the two parallel 10 Gb/s channels Die : 8mm x 5.6mm 17mm x 20 mm x 4 mm package Aggregate data rate : 20 Gb/s Total power : 2.5 W A typical extinction ratio of 5 6 db is achieved at the output of the TX with rise and fall times of 28 ps. <Single ended XFI compatible RX output eye diagram> <TX optical output eye diagram>
Experimental Results <BER versus optical power at the PD> <Receive CDR jitter tolerance> <Receive CDR jitter transfer> Data rate : 10.3125 Gb/s, receiver sensitivity of 19.5 dbm for a BER of 10 12, receiver overload level : 0 dbm, dynamic range of almost 20 db, transmitter electrical input sensitivity : 25 mv pp CDR jitter tolerance : relative to the 802.3ae specification CDR jitter transfer bandwidth : 7 MHz, less than 1 db of jitter peaking
Conclusion A complete 20 Gb/s optical transceiver system has been demonstrated, integrating key optical and electrical components on a single substrate using a 0.13 µm CMOS SOI process. Advantage : reduced size, power consumption, and package integration complexity
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