A Passive Filter Aided Timing Recovery Scheme Faisal A. Musa, - PowerPoint PPT Presentation

A Passive Filter Aided Timing Recovery Scheme Faisal A. Musa, Anthony Chan Carusone Department of Electrical and Computer Engineering U i University of Toronto it f T t

Outline Outline • Introduction Introduction • Baud-rate timing recovery (TR) schemes • Passive filter Passive filter • Measurement Results • Conclusions 2

Introduction Introduction Timing Recovery Techniques CDR Deductive Deductive Inductive Inductive (e.g. non-linear spectral line) Non-linear or Bang-bang Linear (e.g. Hogge) Edge-sampled Baud-rate (focus of this work) 3

Introduction Introduction Analog Signal Processor Front-End Data Data Timing Information Baud-Rate Edge-sampled 4

Introduction Introduction • Why baud-rate over edge-sampled? y g p 1. Reduced clock sampling phases results in less power in the VCO and p phase detector. 2. Better performance in the presence of p p ISI and random noise. [F. Musa and A. Chan Carusone,``Modeling and Design of Multilevel Bang-bang CDRs in the Presence of ISI and g g Noise,’’ IEEE Transactions on Circuits and Systems I: Regular Papers , Vol. 54, No. 10, October 2007.] 5

Baud-Rate TR Schemes Baud Rate TR Schemes • Baud-rate architectures for serial links: Baud rate architectures for serial links: 1 1. Integrating front-end based clock recovery Integrating front-end based clock recovery 2. 2 Mueller Muller PD based clock recovery Mueller-Muller PD based clock recovery 3 3. Minimum Mean Squared Error (MMSE) timing Minimum Mean-Squared Error (MMSE) timing recovery [This work] 6

Baud-Rate TR Schemes Baud Rate TR Schemes • Integrating Front-End Based PD [Emami-Neyestanak, A.; Palermo, S.; Hae-Chang Lee; Horowitz, M.;, [Emami Neyestanak, A.; Palermo, S.; Hae Chang Lee; Horowitz, M.;, VLSI Symposium 2004] : • PD requires specific 4-bit patterns 7

Baud-Rate TR Schemes Baud Rate TR Schemes • Mueller-Muller Timing Recovery [ IEEE Trans. on Comm. , 1976; Balan JSSC 2005 ] [ IEEE Trans. on Comm. , 1976; Balan JSSC 2005 ] [ ] − ≈ τ + − τ − 2 ( ) ( ) X A X A A h T h T − − 1 1 k k k k k b k b • True only for uncorrelated random data 8

Baud-Rate TR Schemes Baud Rate TR Schemes • MMSE PD based CDR (This work): 2 = = − + τ 2 [ ] [{ ( )} ] E E e E A y kT k k k b k e k � MMSE updates the MMSE updates the sampling phase, sampling phase, τ k p p g p g p , , k k k to minimize e to minimize e k 2 : 2 k 2 [ ] dE e τ τ = = τ τ − k + 1 τ k k d e k 2 k + τ ( ) dy kT = τ + μ 2 b k e d τ τ k k d τ k k 9

Sign-Sign MMSE Sign Sign MMSE e k ⎡ ⎤ + τ ( ) dy kT τ τ = = τ τ + + θ θ 2 2 sgn[ sgn[ ] ] sgn sgn b k ⎢ ⎢ ⎥ ⎥ e e bb bb + 1 τ k k k ⎣ ⎦ d k ⇒ Bang bang timing recovery ⇒ Bang-bang timing recovery 10

Baud-Rate TR Schemes Baud Rate TR Schemes • • Advantages of MMSE: Advantages of MMSE: More robust than other baud-rate techniques techniques since since there there are are no no constraints on the input data. • Disadvantages: R Requires slope and error information. i l d i f ti 11

Error-Signal Free Sign-Sign MMSE Error Signal Free Sign Sign MMSE e k ⎡ ⎤ + τ ( ) dy kT τ = τ + θ sgn[ ] sgn ⎢ k ⎥ e + 1 τ k k bb k ⎣ ⎦ d k ⎡ ⎡ ⎤ ⎤ + τ ( ) dy kT ⎡ ⎤ τ ≈ τ + θ + τ + τ sgn ( ) ( ) k ⎢ ⎥ y kT dy kT ≈ τ + θ + τ + 1 sgn[ ( )] sgn τ k k bb k ⎢ k ⎥ y kT ⎣ ⎦ d τ k bb k k ⎣ ⎦ d k 12

Error-Signal Free Sign-Sign MMSE Error Signal Free Sign Sign MMSE ⎡ ⎤ + τ ( ) dy kT τ τ = = τ τ + + θ θ sgn[ sgn[ ] ] sgn sgn ⎢ ⎢ k ⎥ ⎥ e e + 1 τ k k bb k ⎡ ⎤ + τ ⎣ ⎦ d ( ) dy kT k τ ≈ τ + θ + τ sgn ( ) k ⎢ ⎥ y kT + 1 τ k k bb k ⎡ ⎤ + τ ⎣ ⎦ ( ) d dy kT ≈ τ + θ + τ k sgn[ ( )] sgn ⎢ k ⎥ y kT d τ τ k bb k ⎣ ⎣ ⎦ ⎦ d k This work 13

Slope Detection Schemes Slope Detection Schemes Lossy Integrate Integrators & Dump Slope Slope Input I t Input ∫ ∫ Data CLK Integrate and Dump ∫ aided Slope Detector T b T b Data Slope Active Filter aided CLK (b) Slope Detector (a) (a) Data Input Slope Passive Filter aided Slope Detector (c) [Thi [This work] k] 14

Choice of RC time constant Choice of RC time constant • For 10-Gb/s data, the RC ti RC time constant was t t chosen to be 10ps: R = 200 Ω , C = 50 fF Data Data Slope Slope Data Input f Slope 1/2 π RC >> 0.5 f bit 15

Passive Filter Passive Filter Inductors improve • bandwidth without compromising the relative phase shift l ti h hift between the data and slope paths. 16

Die Photo Die Photo 0.18 μ m CMOS; Die area=1.1 mm 2 17

Measurement Results Measurement Results Network Analyzer Measurements: Data Path Bandwidth (Measured)=6-GHz. S 21 in Slope Path increases @ 20dB/dec S 21 in Slope Path increases @ 20dB/dec. 18

Measurement Results Measurement Results DATA PATH OUTPUT SLOPE PATH OUTPUT 19

Measurement Results Measurement Results • External Timing Recovery: 20

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Conclusions Conclusions • A passive filter that provides simultaneous low-pass p p p and high-pass characteristics was presented. • The high-pass transfer characteristic is utilized to provide slope information that is aligned with the low- provide slope information that is aligned with the low pass data output. • Data and slope signals from the passive filter can be used to recover a clock based on modified MMSE used to recover a clock based on modified MMSE timing recovery. • Prototype passive filter was used with external components to recover a 2-GHz clock from a 2-Gb/s 2 GH l k f 2 Gb/ 2 31 -1 random data sequence. 22

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