SI Signal interty G C Visser G C Visser

Trends. History. BER versus SNR. (In a nutshell) Inter Symbol Interference (ISI) NRZ data steam & NRZ signal bandwidth. Needed bandwidth of the channel. Transmission channel. Real world examples. Tools at NIKHEF for SI. Topics G C Visser 2

Serial interfaces on FPGA (20nm) are 30,5 Gb/s capable. 100G Ethernet is already standardized (interconnect to optical module is 4 x 25Gb/s or 10 x 10Gb/s) GBT/Velopix Links 5.125Gb/s & Gb/s. (Future) Big vendors are also working on multilevel coding (PAM-4) Trends G C Visser3

Example of 100G module G C Visser4 100GBASE-LR4 10km CFP4 Optical Transceiver FTLC1141RDNL Optical stuff is nice, butt it still needs connected to our electronics.

In old telegraphy lines, more than 50km, it was not possible to transmit more than 15 words per minute. The first trans Atlantic cable (1860), speed few words per hour. The telegraphy equations, witch are the fundament of transmission lines are, from this area. History G C Visser5

Band with limited, the ocean cable (extra capacity to ground due sea water) thus bad impulse response. Most of modern channels are still bandwidth limited in respect to symbol time. So it will distort the symbol. History > Our time G C Visser6

Bit Error Rate G C Visser7 When a channel is free of Inter Symbol Interference (ISI). The Number of fault received bits (BER) is determinate by used modulation scheme and signal and noise ration (SNR) This is also thru of optical transmission.

Previous bits residual state can distorts the current bit. ISI is caused by, Reflections, Channel resonances, Channel loss & Dispersion. ISI kills a goods BER. Pulse response. Inter-Symbol Interference (ISI) G C Visser8 c(t) Delay/length channel

An NRZ data stream can be modelled as a superposition of isolated 1”s & 0”s, NRZ Data stream (PAM-2) G C Visser9 NRZ Stream

Channel response to NRZ stream is equivalent to the super position of isolated pulse responses. NRZ Data modelling G C Visser10

Channel Pulse Response G C Visser11 y(t) = […, 0.003, 0.036, 0.540, 0.165, 0.065, 0.033,0.02,…] k = […, -2, -1,0, 1, 2,3, 4, ……]

A Non Return to Zero Signal has a Nyquist frequency of Fnyq = Bitrate/2. Bandwidth of a NRZ signal 1 G C Visser12 Time domain 10 Gbps. Frequency domain FFT Majority of the signal power is 10Ghz bandwidth!! So a channel should we well design is this case up 10Ghz.

FFT fun on a real-time scope(30 GHz bw). Bandwidth of a NRZ signal 2 G C Visser13 F1 2*F 3*F F = 5.125GHz Data rate Gbps

Causes ISI resume G C Visser14 Band-limited channels means dispersion (our nice short pulses get up) Attenuation > reduction in amplitude. Dispersion > spreading of the pulse. Reflections > Due impedance differences. DispersionReflections Skin-effect, dielectric loss. Impedance mismatch (connectors, via’s,device packages, etc…..)

S parameters data of channel, obtained with the VNA. Use of built in models in the simulators. Use of vendor s parameters of connetors IBIS-AMI models. Simulation the complete channel in a EM solver. Modelling the channel G C Visser15

Frequency response channel G C Visser16 50 Ω Microstrip line 50cm long, has 6.8 dB of loss at 5GHz.

Impulse response G C Visser17 ISI

Minimize the insertion loss. Minimize reflections in the channel (example use of backdrilled/laser via’s) Provide a well impedance match over the channel. Pre emphases at the TX. Ad a CTLE on the end of the channel to compensate the high frequency loss. Impleted a DFE (decision feed back equalizer) to combat pre cursor and post cursor isi. Can we improve it? G C Visser18

Continuous Time Linear Equalizer. Is a peaking amplifier, with in inverse frequency slope of the channel. Should be adjusted for the channel. So modelling of the channel is required, to obtain the, right zero’s and poles, for the CTLE. Can cancel both pre cursor and long tail isi. CTLE 1 G C Visser19

PBRS Sequence & CTLE G C Visser20 Model of CTLE

CTLE circuits examples G C Visser21 (not often used)

A CTLE is general limited to 1 order compensation. Amplifiers noise and cross talk. (DFE and FIR EQ don’t do that) While signal to distortion ratio (ISI) is improved, the SNR remains unchanged. CTLE Limitations G C Visser22

Output driver of GWT TSMC 130nm. To be used in the VeLo upgrade. Cable model. And real measured S-Parameters of the a cable, as prosed to use in the system. Example, of a real world channel. G C Visser23 One meter flex/capton GWT Driver FLEX

Driver stage (Velopix) G C Visser24 Bond wire Pre emp circuit 2 x

Results with cable model G C Visser25

Results with measured s parameters G C Visser26

Cheap cables, around 70 euro’s Twinax 100 Ohm. Up to 7 meters. Standardized by SFF Quite high insertion loss. Is not working well the SPIDER-TPX board. 10G Ethernet over passive SFP cable G C Visser27

CTLE & Cable test bench G C Visser28 Measurement data cable. Measured with the VNA. Measurement data CTLE, provided by the manufacturer (Texas instruments).

CTLE in action G C Visser29 Bypass_EQCTLE 0On 1Off So now we have a flat channel. Insertion loss

Eye test bench G C Visser30 Measurement data cable (NIKHEF). Measurement data CTLE, provided by the manufacturer. IBIS pin package model Marvell 10G PHY

Results CTLE 7Meter cable CLTE = 36 (on) G C Visser31 Launch Cable End CableAfter CTLE

Measured Results CTLE 7Meter cable CLTE = 36 G C Visser32 CTLE 7 meter twinax CTLE onNo CTLE

Simulation software = ADS. Matlab. 4 port Vector Network Analyser (up to 20Ghz) 35 GHz Sample Scope. Tools at nikhef G C Visser33

Questions? G C Visser34 QRZ?