Reducing jitter utilising adaptive pre-emphasis FIR filter for high speed serial links Marius Goosen Supervisor: Prof. Saurabh Sinha Microelectronics & Electronics Group Thursday, 16 April 2015 Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha

Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha Agenda Background High speed serial links on copper channels Frequency dependant distortion Deterministic jitter Adaptive pre-emphasis Pilot signaling and peak detection Simulation results Experimental results Conclusion 2

Background M-data lines combined into a high speed serial data line Less skew between lines Higher bandwidth capability Lower pin count and cost of implementation Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha 3

Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha High speed serial links ReferenceData rateTechnologyPre-emphasis [1]1 Gb/sCMOSNone [2]5 Gb/sCMOS3-tap [3]10 Gb/sCMOS5-tap [4]10 Gb/sBiCMOSNone [1] C.Y. Yang and Y. Lee, “A 0.18 μm CMOS 1 Gb/s serial link transceiver by using PWM and PAM techniques”, IEEE International Symp. on Circuits and systems, Vol. 2, pp , Kobe, May [2] C.H. Lin, C.H. Wang and S.J. Jou, “5 Gbps serial link transmitter with pre-emphasis”, IEEE Proc. of the 2003 Asia South Pacific design automation conf., Kitakyushu, pp , Jan [3] M. Li, T. Kwasniewski, S. Wang and Y. Tao, “A 10 Gb/s transmitter with multi-tap FIR pre-emphasis in 0.18μm CMOS technology”, IEEE Proc. of the 2005 Asia South Pacific design automation conf., Shanghai, pp , Jan [4] D.J. Friedman, M. Meghelli, B.D. Parker, J. Yang, H.A Ainspan, A.V. Rylyakov, Y.H. Kwark, M.B. Ritter, L. Shan, S.J. Zier, M. Soma and M. Soyuer, “SiGe BiCMOS integrated circuits for high speed serial communication links”, IBM J. Res. & Dev., Vol 47, No 2/3, Mar

Frequency dependant distortion: Package parasitics Introduces frequency dependant devices 5 Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha Inductance a problem: Thicker bond wires Use multiple bond wires Use tape bonding ≈ fF ≈ 1 nH/mm

Frequency dependant distortion: Copper backplane channel ● Copper channel loss: Conductor loss due to skin effect: Where R skin represents a frequency dependent resistor attenuating the signal: Loss due to dielectric: Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha 6

Frequency dependant distortion: Copper backplane channel ● ● 7 Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha

Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha Frequency dependant distortion: Channel response Loss of GHz Severe frequency dependent distortion 8

Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha Deterministic jitter Deterministic jitter: –Duty cycle distortion –Data dependent jitter DDJ caused by this frequency dependent distortion DDJ causes uncertainty in pulse edges 9 Unit interval Ideal sampling instant Error region

Pre-emphasis and implementation Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha 10 I TAP0 I TAP1 I TAPN

Adaptive pre-emphasis 11 Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha Conventional pre-emphasis –Externally adjustably filter taps –Fixed filter taps Adaptive pre-emphasis –Automatically finds optimal filter taps –Does not require a characterised channel Requires characterised channel

Pilot signaling and peak detection ● 12 Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha

Pilot signaling and peak detection ● ● Representing the channel and FIR filter as impulse response For the first pilot signal: For the second pilot signal: 13 Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha

Design and implementation overview 14 Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha 7 μA / 0.35 mV

Mathematical simulation results ● 15 Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha

Mathematical simulation results ● ● 16 Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha

Mathematical simulation results ● ● ● 17 Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha

Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha Circuit simulation results ●

Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha Circuit simulation results ● ● 19

Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha Experimental results ● μm x 670 μm 340 μm x 160 μm Approximately 1600 transistors Area = 0.725mm 2 4 mm

Experimental results ● ● 21 Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha TX RX OUT+ OUT- Shift IN Shift OUT ADJ OUT EOC IN CLK DATA ADJ OUT IN-IN+ 2 Biasing pads 4 Biasing pads 11 cm 11.5 cm

Experimental results ● ● ● Transmitter –Working with a single filter tap –14 % smaller swing –Unable to move to other states Receiver –Pulses generated from TX signals –Correct pulse width – too low amplitude to switch CMOS logic 22 Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha ADJ SFT

Experimental results ● ● ● ● Pulse generation circuit depends on an RC time constant –Used in a feedback loop –R determines: Charge rate Discharge rate –R  Biased PMOS transistor Achieve constant charge and discharge rate Too slow, hence CMOS output buffer not properly switched. Corner analysis 23 Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha

Experimental results ● ● ● ● Static power dissipation –Transmitter Power dissipation = 36 mW –Calculated ≈ 32.5 mW (with one active filter tap) –Receiver Power dissipation = 19.8 mW –Calculated ≈ 18 mW 24 Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha SpeedSwingFilter tapsPower Simulated5 Gb/s300 mV6< 70 mW 10 Gb/s200mV6< 70 mW

Conclusion Possible “easy” solution for bandwidth problems –One button high speed serial link Speed tests still need to be performed Pulse generation circuit should be redesigned –Produce higher integrity signal 2 international IEEE conference articles –M.E. Goosen, S. Sinha, A. Müller and M. du Plessis, “A low switching time transmitter for high speed adaptive pre-emphasis serial links,” Proc. of IEEE CAS 2009, pp , Sinaia, Oct –M.E. Goosen and S. Sinha, “Analysis of Adaptive FIR Filter Pre-emphasis for High Speed Serial Links,” Proceedings: IEEE Africon 2009, Sept. 2009, Nairobi, Kenya. 1 local conference article –M.E. Goosen and S. Sinha, “Adaptive FIR filter pre-emphasis for high speed serial links,” Proc. of the South African conf. on semi and superconductor technology (SACSST), Stellenbosch, pp , 8-9 April International Journal paper submission 25 Departement Elektriese, Elektroniese & Rekenaar-Ingenieurswese Department of Electrical, Electronic & Computer Engineering Kgoro ya Merero ya Mohlagase, Elektroniki & Bointšinere bja Khomphutha

Feedback/questions Marius Goosen Carl & Emily Fuchs Institute for Microelectronics Dept. Electrical, Electronic & Computer Engineering University of Pretoria Pretoria 0002 Tel: +27-(12) Acknowledgement The authors would like to thank ARMSCOR, the Armaments Corporation of South Africa Ltd, (Act 51 of 2003) for sponsoring this study.