Re: [802.3_100GCU] Item 3: Port type. 802.3bj Consensus Building Group - Channel Specifications

["Mellitz, Richard" <richard.mellitz@xxxxxxxxx>]

A 4 pole Butteworth-Thompson  minimum phase filter might be:

 

>> f=10e6:10e6:20e9; bw1=2.613126; bw2=3.4142136; bw3=2.613126; fc=13e9*1.5;

 

>> rr_filter=(1+bw1*1i*f/fc+bw2*(1i*f/fc).^2+bw3*(1i*f/fc).^3+(1i*f/fc).^4).^-1;

 

>>  subplot(2,1,1); plot(f,20*log10(abs(rr_filter))); subplot(2,1,2); plot(f,unwrap(angle(rr_filter)));

 

Should we use something like this for the Rx filter?

A 1 pole is  minimum phase.  So Tx filter should be OK unless we would like to add more poles for some physical reason.

 

… Rich

 

From: Ran, Adee [mailto:adee.ran@xxxxxxxxx]
Sent: Sunday, June 10, 2012 2:50 PM
To: STDS-802-3-100GCU@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_100GCU] Item 3: Port type. 802.3bj Consensus Building Group - Channel Specifications

 

RX bandwidth filter and TX edge filter should naturally be lower for PAM4 – about half the bandwidth or NRZ – otherwise crosstalk generation and sensitivity are unnecessarily high.

 

These filters should include phase, not just magnitude as in moore_01_0311. Phase is significant in the time domain. It is still multiplication, but with complex values.

 

For the RX filter phase and magnitude we can assume Butterworth filter, which has a rather simple transfer function (see Wikipedia or more professional sources) and is an approximation for realizable filters.

 

As for the TX filter, can anyone suggest which filter is adequate? Is there a justification for 2^nd order and are the poles real or complex conjugate?

 

 

</Adee>

 

From: Mellitz, Richard [mailto:richard.mellitz@xxxxxxxxx]
Sent: Friday, June 08, 2012 5:21 PM
To: STDS-802-3-100GCU@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_100GCU] Item 3: Port type. 802.3bj Consensus Building Group - Channel Specifications

 

Should filters be different per port type?

 

…Rich

 

From: Mellitz, Richard [mailto:richard.mellitz@xxxxxxxxx]
Sent: Friday, June 08, 2012 10:19 AM
To: STDS-802-3-100GCU@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_100GCU] Item 2: preprocessing s-parameters. 802.3bj Consensus Building Group - Channel Specifications

 

Perhaps a convenient way to look at TX/RX filtering is convolution of the following.

 

1.       Tx Voltage Amplitude scaling (for NEXT, FEXT, and THRU not coding which will be done in a later algorithm )

2.       Tx edge filter (moore_01_0311)

3.       Rx bandwidth filter (moore_01_0311)

4.       Tx/Rx block return loss filters (gamma,moore_01_0311)

 

The first three are a straight convolution and with is multiplication in the frequency domain.

 

The lasts is a chain matrix convolution of RL under worst +1 or -1 reflection coefficient  phase conditions and in the frequency domain may look like this

 

sdd21=sdd21.*(1.-gamma_rx)./(1.- sdd11.*gamma_tx + sdd22.*gamma_rx +sdd21.^2.*gamma_tx.*gamma_rx -sdd11.*sdd22.*gamma_tx.*gamma_rx);

 

…Rich