Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline Receiver. D. Dunwell and A. Chan Carusone University of Toronto

Transcription

1 Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline Receiver D. Dunwell and A. Chan Carusone University of Toronto

2 Analog Front End Adaptation Analog Front-End (AFE) Digital Back End Channel ADC AMP S2D EQ Driver Out Gain control EQ control Automatic Adaptation Control signals should be generated automatically and should be able to adapt to a variety of channel conditions Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 2 of 21

3 Outline Adaptation: existing and proposed technique Theory and implementation Simulated and measured results demonstrate validity Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 3 of 21

4 Analog Adaptation of EQ Filters consume large area EQ Driver Minimizing difference in high frequency content does not guarantee best equalization HP filter rectifier EQ control HP filter rectifier [1] Baker, ISSCC, 2006 Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 4 of 21

5 BER-Based Adaptation of EQ Ensures optimal eye opening but very complex and slow to converge threshold control channel output clk1 BER-based adaptation Rx Data T T T clk2 CDR DFE tap control clk3 clk1 clk2 clk3 [6] Chen, JSSC, 2008 Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 5 of 21

6 Proposed Architecture Test Setup Prototype I.C. Slicer Driver Data channel output VGA DAC EQ DAC DAC Slicer Driver Adaptation can run continuously or in start-up calibration Gain Control EQ Control threshold Adaptation Algorithm low-speed ADC Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 6 of 21

7 Variable Gain Preamplifier Gain controlled by analog signal V gain V gain V DD R fixed M2 V biasp Increased V gain results in decreased preamplifier gain V channel R f M1 V out V biasn M3 [11] Dunwell, ISCAS, 2010 Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 7 of 21

8 Analog Split-Path Equalizer High frequency peaking controlled by analog signal V eq Increased V eq results in decreased low frequency gain and increased high frequency peaking [10] Zhang, JSSC, 2005 V eq Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 8 of 21

9 EQ and VGA Simulation Results Variable gain amplifier: 8 db gain control Flat BW from 0 to 10 GHz Equalizer: 8 db low freq gain control high freq peaking G a in (d B ) Vgain = 0.8 V Vgain = 2 V Frequency (GHz) Gain (db) Frequency (GHz) Veq = 0.25 V Veq = 0.7 V Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 9 of 21

10 Outline Adaptation: existing and proposed technique Theory and implementation Simulated and measured results demonstrate validity Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 10 of 21

11 PDF Indicates Vertical Eye Quality x Transmitted Signal x Received Signal V TH channel V RH V TL PDF t V RL PDF t x is a random variable created by sampling the PRBS data at the midpoint of each bit Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 11 of 21

12 Threshold Sweep to Obtain PDF CDF = % "1"s V RH V CM V RL threshold sweep 50% 0% V CM threshold PDF peak indicates equalization Slicer Low-speed ADC Vout PDF Slope of Vout Threshold at peak = V RH threshold control V CM threshold Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 12 of 21

13 Outline Adaptation: existing and proposed technique Theory and implementation Simulated and measured results demonstrate validity Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 13 of 21

14 Simulation Results 10 m Cable 125 mv 30 mv Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 14 of 21

15 Simulation Results Gain Setting 100 mv Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 15 of 21

16 Prototype in 65-nm CMOS Vdd = 1.2 V Adaptation performed off-chip with minimal additional hardware Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 16 of 21

17 1010 Pattern vs PRBS Data (2 Gb/s) High peak = narrow PDF Threshold at peak = eye amplitude Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 17 of 21

18 Measured Results 2Gb PRBS Step 1: Sweep V eq to find peak PDF Step 2: Sweep V gain to set amplitude Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 18 of 21

19 Varying Channel Conditions Coax Cable: 10 Gb/s (5 Gb/s for 30 m cable) PCB Traces: 4 Gb/s for all lengths Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 19 of 21

20 Eye Diagrams 10 Gb/s 10 m coaxial cable channel output Receiver output after adaptation Vertical: 100 mv/div Horizontal: 50 ps/div Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 20 of 21

21 Conclusions Proposed adaptation technique : Quickly optimizes vertical eye opening over a variety of channel types and lengths. Optimizes equalizer peaking and preamplifier gain with a single set of data. Can run continuously on parallel data line or at start up with minimal added circuitry. Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 21 of 21

22 Thank You Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 22 of 21

23 Channel Loss 0 S21 vs. Frequency m m S21 [db] m [Hz] Gain and Equalization Adaptation to Optimize the Vertical Eye Opening in a Wireline RX 23 of 21