Presentation on theme: "LVDS 280MHZ link SPD VFE PS VFE"— Presentation transcript:
1LVDS 280MHZ link SPD VFE PS VFE Cable pre-selection.Cable model.Eye diagrams.Bit Error Ratio (BER) measurements.Summary.BCN – CFD-BCN meeting – 10/10/2003
2I. Cable pre-selection.Several cat7 and cat6 SSTP cables will be tested:Infra+ cat7 patch cable (flexible) (datasheet)Infra+ cat7 vertical cable (rigid)* (datasheet)Infra+ cat6 vertical cable (rigid)*?Nexans (Alcatel) cat7 patch cable ()* (datasheet)Cat5e? Xtalk? Skew?Cat7 rigid cable seems to have the better specs on skew and bandwidth.Problems with rigid cables:Section too big?Cost?Perhaps it is not possible to mount RJ45 connectors on cat7 rigid cable. Solution: MiniC connector, solder to boards ... (Infra+ connectors).
3II. Cable model. RLGC model of cable (Theory of twisted pair cables). Skin effect and dielectric looses limit the bandwidth.How to simulate the cable response? Hspice W-model: how to calculate the cable parameters?How to tune the compensation network? First order model for cable like in (High Speed Links for ATLAS).
4III. Eye diagrams. Needed to validate the link within std LVDS levels. Test equipment requirements:BW 3 * 0.35/trise ( 1 GHz) for trise of 1ns.Sampling rate 4 * BW ( 4 GS/s) (for proper reconstruction a a DSO)Differential probeLAL measurement forDS90CR483/484 chipset
5III. Bit Error Ratio (BER) measurements. Several test patterns will be used (miming IEEE std):High Frequency.Low Frequency.Deterministic jitter.Random test pattern.Test pattern (8K per bit) will be generated on a PC and transmitted to Cyclone or Stratix (Altera) Dev. Board operated at 40MHz to continuously check for errors.Automatic synchronization for different cable lengths (cycle and phase)10 bit error counter bit will be enough?Needed to identify the word of the frame when when error happens?It is possible to generate pseudo-random test pattern with a LFSR register.References: ATLAS-LEB2000 and VELO-LHCb.
6IV. Summary.Several cable will types and lengths (from 10m to 30m) will be tested.The first step is to characterize the cable and tune the compensation network for each type of cable and length.After reducing the candidates extensive BER measurements will be performed.Sensitivity to the jitter of 40 clock of the serializer needs to be tested, since is supplied through a 25 m cable from Control Board.Performance of PIN diode level shifter (before serializer) will also be tested.Possible level shifter in LVDS link will be tested (at 280MHz!)