Report

2011-1 Special Topics in Optical Communications Electronic Circuits for Optical Systems : Transimpedance Amplifier (TIA) Jin-Sung Youn ([email protected]) High-Speed Circuits & Systems Laboratory High-Speed Circuits & Systems Laboratory 2011-1 Special Topics in Optical Communications Contents 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 High-Speed Circuits & Systems Laboratory 2 2011-1 Special Topics in Optical Communications Electrical Interconnects 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 High-Speed Circuits & Systems Laboratory 3 2011-1 Special Topics in Optical Communications Optical Interconnects Direct modulation Photodetector - Driving circuits Current-voltage (I-V) conversion - VCSEL component / circuits External modulation - Laser - Modulator - Driving circuits High-Speed Circuits & Systems Laboratory 4 2011-1 Special Topics in Optical Communications Requirements for The First Block RF Receiver Front-End Optical Receiver Front-End (Voltage / Power) Gain (Transimpedance) Gain (Channel) Bandwidth (Broadband) Bandwidth Noise figure (Input) Noise current High-Speed Circuits & Systems Laboratory 5 2011-1 Special Topics in Optical Communications Receiver Basics (Transimpedance) Gain G ain R D (Broadband) Bandwidth BW 1 2 R D C p d (Input) Noise current ► Resistor performs a current-to-voltage conversion. I 2 n , in kT 2 R DC pd Trade-off between gain, speed and noise !! High-Speed Circuits & Systems Laboratory 6 2011-1 Special Topics in Optical Communications Integrated Total Noise Output Noise Spectrum of Circuit Circuit bandwidth ↑ Integrated total noise ↑ High-Speed Circuits & Systems Laboratory 7 2011-1 Special Topics in Optical Communications Bandwidth vs. Noise BW = 1.4 fB No ISI High noise BW = 0.35 fB High ISI Low noise BW = 0.7 fB No ISI Medium Noise * ISI: Inter-Symbol Interference ** fB: data rate High-Speed Circuits & Systems Laboratory 8 2011-1 Special Topics in Optical Communications Bandwidth vs. Noise Inter-Symbol Interference (ISI) vs. Noise Optimum bandwidth depends on data rates !! High-Speed Circuits & Systems Laboratory 9 2011-1 Special Topics in Optical Communications Gain vs. Noise Signal-to-Noise Ratio (SNR) Noise Ringing Gain SNR S ignal [A pp ] Bandwidth N oise [A rm s ] High-Speed Circuits & Systems Laboratory Noise 10 2011-1 Special Topics in Optical Communications Receiver Basics - Example ** p-i-n photodetector ** Low impedance High impedance (N.Feng et al., Optics Express, 2010) 1kΩ (1) R = 0.9 A/W (TM polarization) IIN = 1.8 mApp @ 0 dBm (ideal extinction ratio) (2) Cpd = 200 fF RC time constant High-Speed Circuits & Systems Laboratory High bandwidth (fp = 15.9 GHz) Low sensitivity (Vo,pp = 9 mVpp) High noise 11 Small bandwidth (fp = 0.8 GHz) High sensitivity (Vo,pp = 1.8 Vpp) Low noise 2011-1 Special Topics in Optical Communications Transimpedance Amplifier (TIA) (Shunt-Shunt) Feedback Amplifier - Low input impedance & High transimpedance !! (Transimpedance) Gain R in 1 A 1 RF G a in Rin A A 1 RF (Broadband) Bandwidth A BW A 1 2 R F C p d (Input) Noise current I n ,in 2 High-Speed Circuits & Systems Laboratory 12 4 kT RF 2 V n ,A 2 RF 2011-1 Special Topics in Optical Communications Comparison But, RF ↑ Rin ↑ High-Speed Circuits & Systems Laboratory 13 2011-1 Special Topics in Optical Communications Advanced Techniques [1] • Shunt Peaking Inductor implementation : (a) Spiral inductor (b) Active inductor (a) Large power consumption & chip area (b) PVT variation High-Speed Circuits & Systems Laboratory 14 2011-1 Special Topics in Optical Communications Advanced Techniques [2] Input (current) Buffer Stage Common-gate TIA (CG-TIA) Regulated-cascode TIA (RGC-TIA) R in Rin 1 g m 1 1 g m B R B Rin R in 1 g m1 Low input impedance a) higher input noise current b) Relatively low transimpedance gain G = RD // (RF/(A+1)) High-Speed Circuits & Systems Laboratory 15 2011-1 Special Topics in Optical Communications Advanced Techniques [3] Current-mode Transimpedance Amplifier (CM-TIA) R in 1 g m1 Rin Low input impedance a) Higher input noise current b) Low transimpedance gain @ low supply voltage G = Rout,M6 // Rout,M5 High-Speed Circuits & Systems Laboratory 16 2011-1 Special Topics in Optical Communications Receiver Front-End Integration Photodetector and electronic circuits should be integrated on a single chip for optical interconnect applications. Photodetector 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] High-Speed Circuits & Systems Laboratory 17 2011-1 Special Topics in Optical Communications Recent Research Topics Power consumption of optical system should be minimized to take over a substantial fraction of interconnect applications. “Receiver-less approach” Requirements • Electronic circuit - Low input MOSFET capacitance - Low input sensitivity • Photodetector - High responsivity - Low junction capacitance (~ fF) Buffer (inverter) chain Avalanche photodetector (> p-i-n photodetector) High-Speed Circuits & Systems Laboratory 18 2011-1 Special Topics in Optical Communications Receiver-Less Approach: Example ** Avalanche photodetector ** (S.Assefa et al., Nature, 2010) (= 1kΩ) (1) R = 0.15 A/W IIN = 0.3 mApp @ 0 dBm (ideal extinction ratio) (2) Cpd = 10 fF RC time constant High-Speed Circuits & Systems Laboratory High bandwidth (fp = 15.9 GHz) High sensitivity (Vo,pp = 300 mVpp) Low noise 19 2011-1 Special Topics in Optical Communications Conclusion 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 !! High-Speed Circuits & Systems Laboratory 20 2011-1 Special Topics in Optical Communications Thank you for listening !! Jin-Sung Youn ([email protected]) High-Speed Circuits & Systems Laboratory High-Speed Circuits & Systems Laboratory 21