Hi Guillaume,
4600 ppm peak-to-peak (45.3 UI) of
sinusoidal modulation at 97 kHz and 1840 ppm pp (6.5 UI) at 270 kHz are OK.
I think that it is important that we have
these two test points on the sloping side of the Jitter Transfer Function (JTF).
The section in between is theoretically a straight line.
Some people had understood that we wanted
to test at 10 kHz or with 14870 ppm pp at 30 kHz and I think that we have to
clarify that these two points exceed the expected frequency deviation range of
the receiver VCO, whereas 97 kHz was selected to be the point where the
receiver CDR should be able to handle deviation as well as jitter tolerance.
Sincerely,
SyntheSys Research, Inc.
(650) 364-1853
From: Guillaume Fortin
(
Sent: Monday, July 21, 2008 12:43
PM
To:
Subject: RE: Receiver JTF
tolerance
Hi Bent,
I agree that the modulation at 97kHz that
we will be applying is likely higher than what would be applied in a reasonable
SAS-2 system with 30kHz triangular SSC modulation. However, the residual jitter
that results from the 45.3UIpp modulation at 97kHz creates a 0.1 UIpp residual
jitter after the JTF and thus meets the SAS-2 specification, that is to say
that a compliant transmitter could generate it. If the transmitter is allowed
to generate this jitter, we must ensure that the receiver can track it.
By ensuring that a compliant transmitter
never produces more than 0.1UI of residual jitter after the JTF and ensuring
that a receiver accepts an input jitter that is at least 0.1UI after filtering
by the same JTF, we ensure consistency in our analysis of system robustness.
This is what the inverse JTF mask accomplishes.
A 4600ppm-pp sine SSC modulation
would meet the spec so I disagree with the 1.3x factor for triangular vs
sinusoidal. I am not sure that I follow your train of thoughts with the
modulation index. It would seem to me that the modulation index (m = df / fm)
would actually decrease by a factor of 3.23 at 97kHz vs 30kHz since the
modulation frequency increases (30kHz -> 97 kHz) while the df stays constant
(2300ppm * 6GHz = 13.8MHz).
Regards,
Guillaume
From:
Sent: Monday, July 21, 2008 1:16
PM
To: Guillaume Fortin (
Subject: RE: Receiver JTF
tolerance
Hi Guillaume,
The +/-2300 ppm (4600 ppm peak to peak)
deviation may be the same for your proposal, but please realize that the
modulation index will be 3.23 times larger at 97 kHz than it is at 30 kHz.
Further the sinusoidal component of a 5000 ppm peak-to-peak triangular SSC
waveform is merely 3626 ppm at 30 kHz (another factor of 1.3 of difference).
Your proposal therefore is about 4.2 x the
modulation which can be generated at 97 kHz in SAS system. Instead a factor 2
x, which is very close to your peak (not peak-to-peak) values in ppm as
displayed in your graph, will be much more reasonable for receiver testing.
Bent
From:
owner-t10@t10.org [mailto:owner-t10@t10.org] On
Behalf Of Guillaume Fortin (
Sent: Monday, July 21, 2008 8:29
To:
Subject: RE: Receiver JTF
tolerance
You are correct Bent: the frequency offset
values are peak values.
It is true that the frequency offset at
30kHz is too large if we scale the SJ modulation by the inverse-JTF below
~2MHz. This is why my proposal is to stop at 97kHz, which is the point at which
the SJ modulation amounts to +/-2300ppm, which is the maximum SSC modulation
that has to be tracked according to the SAS-2 spec.
I will create figures for the SJ mask that
should make things clear.
Regards,
Guillaume
From:
Sent: Friday, July 18, 2008 2:40
PM
To: t10@t10.org; Guillaume Fortin
(
Subject: Receiver JTF tolerance
Hi Guillaume,
There appears to be an error going from the equation for
frequency offset on page 9 to the figures on page 10 and forward in your
presentation document 08-248r0. When the offset plotted is only half of the
peak-to-peak offset as the max and min values of
These are extremely large values considering that the
peak-to-peak transmitter deviation is 5000 ppm plus/minus frequency tolerance.
The transmitter SSC waveform is often a triangular waveform in which the 30 kHz
sinusoidal frequency component is merely 3624 ppm peak-to-peak followed by a decreasing
amount at each odd harmonic of 30 kHz.
I do not see any source of ppm amplification in our SAS
channel. We should certainly make sure that the receivers have some margin
(i.e. that the SSC Waveform becomes a small or insignificant portion of our
jitter budget). 4x margin may however a too much margin. We therefore suggest
that the margin be 2x instead of 4x, this will leave the current ppm frequency
offset numbers as is in the graphs while the UI numbers be half of the values
of your presentation.
Sincerely,
SyntheSys Research, Inc.
(650) 364-1853