This filter
rr_filter=(1+bw1*1i*f/fc+bw2*(1i*f/fc).^2+bw3*(1i*f/fc).^3+(1i*f/fc).^4).^-1;
has the EXACT power spectrum as was used in moore_01_0311 (and clause 85).
rr_filter_POWER= (1+ (1i*f/fc).^8).^-1;
To me these are simple single line equations.
…Rich
*From:* Charles Moore [mailto:charles.moore@xxxxxxxxxxxxx]
*Sent:* Wednesday, June 13, 2012 3:48 PM
*To:* Mellitz, Richard
*Cc:* STDS-802-3-100GCU@xxxxxxxxxxxxxxxxx
*Subject:* Re: [802.3_100GCU] Item 3: Port type. 802.3bj Consensus
Building Group - Channel Specifications
The 4 pole (Tx) and 8 pole 0 phase Butterworth filters in
moore_01_0311 were used strictly for mathematical convenience and were
not intended to be particularly realistic. There is little enough
energy at the 3dB frequency of the filters in most channels so that we
(adam and i) felt that the lack of realism would not be significant.
Adding phase pretty much does away with the mathematical simplicity
with little gain in realism: a 4 pole Butterworth filter has higher Q
poles than anyone is likely to implement on a chip.
charles
|--------------------------------------------------------------------|
| Charles Moore
| Avago Technologies
| APD
| charles.moore@xxxxxxxxxxxxx <mailto:charles.moore@xxxxxxxxxxxxx>
| (970) 288-4561
|--------------------------------------------------------------------|
Mellitz, Richard wrote:
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
<mailto: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]
<mailto:%5Bmailto:richard.mellitz@xxxxxxxxx%5D>
*Sent:* Friday, June 08, 2012 5:21 PM
*To:* STDS-802-3-100GCU@xxxxxxxxxxxxxxxxx
<mailto: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
<mailto: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.
Tx Voltage Amplitude scaling (for NEXT, FEXT, and THRU not coding
which will be done in a later algorithm )
Tx edge filter (moore_01_0311)
Rx bandwidth filter (moore_01_0311)
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