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High-Speed Circuits & Systems Laboratory Electronic Circuits for Optical Systems : Transimpedance Amplifier (TIA) Jin-Sung Youn (jsyoun@tera.yonsei.ac.kr)jsyoun@tera.yonsei.ac.kr High-Speed Circuits & Systems Laboratory 2011-1 Special Topics in Optical Communications
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High-Speed Circuits & Systems Laboratory Contents 2 2011-1 Special Topics in Optical Communications Electrical interconnects vs. optical interconnects Electronic circuits for optical interconnects - Receiver basics - Transimpedance amplifier (TIA) TIA design considerations Advanced (wideband) techniques Recent research topics Conclusion
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High-Speed Circuits & Systems Laboratory 3 Electrical Interconnects 2011-1 Special Topics in Optical Communications Transmitter - Serializer: slow parallel data fast serial data - Phase-Locked Loop (PLL): generate reference clock - Pre-emphasis: compensate high-frequency loss Receiver - Equalizer: compensate high-frequency loss - Limiting amplifier: amplify signal up to digital level - Clock and Data Recovery (CDR): recover synchronous clock and data - De-serializer: fast serial data slow parallel data
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High-Speed Circuits & Systems Laboratory 4 Optical Interconnects 2011-1 Special Topics in Optical Communications Direct modulation - Driving circuits - VCSEL External modulation - Laser - Modulator - Driving circuits Photodetector Current-voltage (I-V) conversion component / circuits
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High-Speed Circuits & Systems Laboratory 5 Requirements for The First Block 2011-1 Special Topics in Optical Communications (Voltage / Power) Gain (Channel) Bandwidth Noise figure RF Receiver Front-EndOptical Receiver Front-End (Transimpedance) Gain (Broadband) Bandwidth (Input) Noise current
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High-Speed Circuits & Systems Laboratory 6 Receiver Basics 2011-1 Special Topics in Optical Communications (Transimpedance) Gain (Broadband) Bandwidth (Input) Noise current ► Resistor performs a current-to-voltage conversion. Trade-off between gain, speed and noise !!
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High-Speed Circuits & Systems Laboratory 7 Integrated Total Noise 2011-1 Special Topics in Optical Communications Output Noise Spectrum of Circuit Circuit bandwidth ↑ Integrated total noise ↑
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High-Speed Circuits & Systems Laboratory 8 Bandwidth vs. Noise 2011-1 Special Topics in Optical Communications BW = 1.4 f B No ISI High noise BW = 0.35 f B High ISI Low noise BW = 0.7 f B No ISI Medium Noise * ISI: Inter-Symbol Interference ** f B : data rate
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High-Speed Circuits & Systems Laboratory 9 Bandwidth vs. Noise 2011-1 Special Topics in Optical Communications Inter-Symbol Interference (ISI) vs. Noise Optimum bandwidth depends on data rates !!
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High-Speed Circuits & Systems Laboratory 10 Gain vs. Noise 2011-1 Special Topics in Optical Communications Signal-to-Noise Ratio (SNR) NoiseRinging Gain Bandwidth Noise
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High-Speed Circuits & Systems Laboratory 11 Receiver Basics - Example 2011-1 Special Topics in Optical Communications High bandwidth (f p = 15.9 GHz) Low sensitivity (V o,pp = 9 mV pp ) High noise Small bandwidth (f p = 0.8 GHz) High sensitivity (V o,pp = 1.8 V pp ) Low noise Low impedanceHigh impedance ** p-i-n photodetector ** (N.Feng et al., Optics Express, 2010) 1kΩ (1)R = 0.9 A/W (TM polarization) I IN = 1.8 mA pp @ 0 dBm (ideal extinction ratio) (2) C pd = 200 fF RC time constant
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High-Speed Circuits & Systems Laboratory 12 Transimpedance Amplifier (TIA) 2011-1 Special Topics in Optical Communications (Shunt-Shunt) Feedback Amplifier - Low input impedance & High transimpedance !! (Transimpedance) Gain (Broadband) Bandwidth (Input) Noise current A R in
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High-Speed Circuits & Systems Laboratory 13 Comparison 2011-1 Special Topics in Optical Communications But, R F ↑ R in ↑
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High-Speed Circuits & Systems Laboratory 14 Advanced Techniques [1] 2011-1 Special Topics in Optical Communications Shunt Peaking Inductor implementation : (a) Spiral inductor (b) Active inductor (a) Large power consumption & chip area (b) PVT variation
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High-Speed Circuits & Systems Laboratory 15 Advanced Techniques [2] 2011-1 Special Topics in Optical Communications Input (current) Buffer Stage Common-gate TIA (CG-TIA)Regulated-cascode TIA (RGC-TIA) R in Low input impedance a) higher input noise current b) Relatively low transimpedance gain G = R D // (R F /(A+1))
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High-Speed Circuits & Systems Laboratory 16 Advanced Techniques [3] 2011-1 Special Topics in Optical Communications Current-mode Transimpedance Amplifier (CM-TIA) R in Low input impedance a) Higher input noise current b) Low transimpedance gain @ low supply voltage G = R out,M6 // R out,M5
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High-Speed Circuits & Systems Laboratory 17 Receiver Front-End Integration 2011-1 Special Topics in Optical Communications Photodetector and electronic circuits should be integrated on a single chip for optical interconnect applications. Responsivity Transimpedance gain [to meet limiting amplifier input sensitivity] Pole frequency - Transit effect - RC time constant TIA Input impedance [to avoid RC time effect] EQ gain [to compensate limited bandwidth] Noise Low input-referred circuit noise [to achieve high SNR at TIA input node] Photodetector
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High-Speed Circuits & Systems Laboratory 18 Recent Research Topics 2011-1 Special Topics in Optical Communications “Receiver-less approach” Electronic circuit - Low input MOSFET capacitance - Low input sensitivity Photodetector - High responsivity - Low junction capacitance (~ fF) Avalanche photodetector (> p-i-n photodetector) Power consumption of optical system should be minimized to take over a substantial fraction of interconnect applications. Requirements Buffer (inverter) chain
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High-Speed Circuits & Systems Laboratory 19 Receiver-Less Approach: Example 2011-1 Special Topics in Optical Communications ** Avalanche photodetector ** (S.Assefa et al., Nature, 2010) (1)R = 0.15 A/W I IN = 0.3 mA pp @ 0 dBm (ideal extinction ratio) (2) C pd = 10 fF RC time constant High bandwidth (f p = 15.9 GHz) High sensitivity (V o,pp = 300 mV pp ) Low noise (= 1kΩ)
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High-Speed Circuits & Systems Laboratory 20 Conclusion 2011-1 Special Topics in Optical Communications Receiver System for Optical Interconnects Current-Voltage Conversion Resistor termination Transimpedance amplifier (TIA) TIA design considerations & methods Advanced (Wideband) techniques Shunt-peaking Common-gate & regulated cascode Recent research topics Receiver-less approach !!
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High-Speed Circuits & Systems Laboratory 21 2011-1 Special Topics in Optical Communications Thank you for listening !! Jin-Sung Youn (jsyoun@tera.yonsei.ac.kr)jsyoun@tera.yonsei.ac.kr High-Speed Circuits & Systems Laboratory
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