[SI-LIST] Re: what's de-emphasis
- From: Istvan Novak <istvan.novak@xxxxxxx>
- To: Adiu <adiu_panli@xxxxxxxxx>
- Date: Mon, 02 Nov 2009 08:40:28 -0500
Adiu,
In terms of resulting waveform shapes, preemphasis and deemphasis in
SerDes are identical. The differentiator is what is your baseline: if
your reference level is the steady state and you boost the first
transition bit, it is called deemphasis. If the level of your first
transitioning bit is the reference and you decrease the level of
subsequent bits, it is called deemphasis. The difference matters only
for the cell design, for the user they should be identical.
Regards,
Istvan Novak
SUN Microsystems
Adiu wrote:
> Thanks for all replies.
>
> My application of this pre/de-emphasis is SerDes signals.
> It is more clear to me now that pre/de-emphasis functions similarly
> (the pulse waveform shape looks same), except that de-emphasis
> produces smaller amplitude.
>
> However, going to the implementation details, I still have some concerns.
> To explain my concerns more clearly, I am attaching a one-page word
> document.
> In the document,
> First, an arbitrary 1v nominal waveform is shown.
> Second, the pre-emphasis implementation block digaram captured from a
> Altera document is shown.
> Third, the pre-emphasis waveform obtained based on the Altera
> implementation diagram is shown. my concern: this waveform seems to me
> more like the de-emphasis waveforms based on the dicussion.
> Fourth, I try to plot the pre-emphasis waveform based on the
> discussion. my concern: is this correct?
>
> Could any one provide me the block implementation diagrams for both
> pre-emphasis and de-emphasis?
>
> Thanks again for everyone's time.
>
> Best regards,
> Adiu
>
> --- On *Sun, 11/1/09, Istvan Novak /<istvan.novak@xxxxxxx>/* wrote:
>
>
> From: Istvan Novak <istvan.novak@xxxxxxx>
> Subject: Re: [SI-LIST] Re: what's de-emphasis
> To: "LY" <long.0.yang@xxxxxxxxx>
> Cc: "Bill Wurst" <billw@xxxxxxxxxxx>, "Adiu"
> <adiu_panli@xxxxxxxxx>, "prasad" <hariprasad.palli@xxxxxxxxx>,
> Joseph.Schachner@xxxxxxxxxx, si-list@xxxxxxxxxxxxx
> Received: Sunday, November 1, 2009, 10:25 PM
>
> If you search the SI-list archives you should find past
> discussions on
> this same topic with more detailed explanations.
>
> LY wrote:
> > Istvan:
> > Could you make it clear about the pre/de-emphasis in
> > telecommunications and SerDes signaling?
> >
> > Long Yang
> > Joan Crawford - "I, Joan Crawford, I believe in the dollar.
> > Everything I earn, I spend." -
> > http://www.brainyquote.com/quotes/authors/j/joan_crawford.html
> >
> >
> > On Mon, Nov 2, 2009 at 08:13, Istvan Novak <istvan.novak@xxxxxxx
> <http://ca.mc354.mail.yahoo.com/mc/compose?to=istvan.novak@xxxxxxx>>
> wrote:
> >
> >> Bill and All,
> >>
> >> Rather than saying that this definition is wrong, we should say
> that
> >> this does not apply to digital SerDes signaling.
> >> If one reads the entire text on wikipedia, it is clear that it
> refers to
> >> telecommunications applications, where the high-
> >> frequency components are in fact suppressed. The unfortunate
> fact is
> >> that deemphasis means different things in
> >> telecommunications and in SerDes signaling.
> >>
> >> Regards,
> >>
> >> Istvan Novak
> >> SUN Microsystems
> >>
> >>
> >> Bill Wurst wrote:
> >>
> >>> Adiu,
> >>>
> >>> As Joe S. indicated, the definition for de-emphasis is clearly
> wrong. A
> >>> more correct way of stating de-emphasis would be:
> >>> De-emphasis: Improving the signal to noise ratio by
> >>> decreasing the magnitude of lower frequency signals
> >>> with respect to higher frequency signals.
> >>> Even with this corrected definition, you will note that what both
> >>> pre-emphasis and de-emphasis accomplish is similar. Thus,
> given the
> >>> same input waveshape, the waveforms output from either process
> will have
> >>> the same shape.
> >>>
> >>> Either pre-emphasis or de-emphasis is usually accomplished at the
> >>> transmitter, while equalization is done at the receiver.
> Although all
> >>> three work in different ways, they all accomplish the same
> purpose,
> >>> i.e., to flatten the frequency response of the overall system by
> >>> compensating for distortions introduced by the transmission
> medium.
> >>>
> >>> Best regards,
> >>> -Bill
> >>>
> >>> /************************************
> >>> / William C. Wurst, PE /
> >>> / billw@xxxxxxxxxxx
> <http://ca.mc354.mail.yahoo.com/mc/compose?to=billw@xxxxxxxxxxx>
> /
> >>> / Advanced Electronic Concepts, LLC /
> >>> / www.aec-lab.com /
> >>> ************************************
> >>> =========================================================
> >>> prasad wrote:
> >>>
> >>>
> >>>> i believe, its a matter of reference with which we are
> defining. since the
> >>>> technique is much evident when we see frequent transitions,
> the amplitude of
> >>>> those bits is higher than the bits having the lesser
> transitons. extending
> >>>> this to a combination of lets say, 0111, the transtion from 0
> to 1 will have
> >>>> higher amplitude than the further 1s. so we say that 0to 1 is
> pre emphasized
> >>>> or 1to 1 is deemphasized w r t 0 to 1.
> >>>>
> >>>>
> >>>>
> >>>> 2009/10/31 <Joseph.Schachner@xxxxxxxxxx
>
> <http://ca.mc354.mail.yahoo.com/mc/compose?to=Joseph.Schachner@xxxxxxxxxx>>
> >>>>
> >>>>
> >>>>
> >>>>> Of the two definitions you got from Google:
> >>>>> Pre-emphasis: " Improving the signal to noise ratio by
> increasing the
> >>>>> magnitude of higher frequency signals with respect to lower
> frequency
> >>>>> signals"
> >>>>> De-emphasis: " Improving the signal to noise ratio by
> decreasing the
> >>>>> magnitude of higher frequency signals with respect to lower
> frequency
> >>>>> signals"
> >>>>>
> >>>>>
> >>>>> The Pre-emphasis definition is acceptable. The De-emphasis
> definition is
> >>>>> clearly wrong, in my opinion. De-emphasis goal is the same,
> to increase
> >>>>> magnitude of higher frequency signals with respect to low
> frequency
> >>>>> signals. It just is a slightly different way to get that
> effect.
> >>>>>
> >>>>> I think pre-emphasis and de-emphasis are much easier to
> understand in the
> >>>>> time domain, rather than the frequency domain.
> >>>>> In the time domain, as text with with one dash per UI
> (transitions don't
> >>>>> appear) :
> >>>>> Each diagram is 4 UI low, 5 UI high, 4 UI low
> >>>>> _
> >>>>> _____ ... ____ ... _
> >>>>> ____
> >>>>> ____ ____ ... ____ ___ ... ____ ___
> >>>>> _ _
> >>>>>
> >>>>> The desired pulse With pre-emphasis With deemphasis
> >>>>> The first UI All but the first UI
> >>>>> after a transition after a transition
> >>>>> is higher amplitude are lower amplitude
> >>>>>
> >>>>>
> >>>>> The reason to do this is because a normal channel attenuates
> high
> >>>>> frequencies more,
> >>>>> so the (relatively) sharp rising edge of a transmitted pulse
> will become
> >>>>> slower
> >>>>> at the far end, and the first UI would not reach the desired
> height by the
> >>>>> middle
> >>>>> of the UI. That is, it would cause the eye opening to be
> reduced.
> >>>>> By having the TX pump out a larger transition, after the
> loss due to the
> >>>>> channel,
> >>>>> at the far end, the signal looks better - more like what we
> desired.
> >>>>> Standards
> >>>>> like PCI-Express don't actually call for pre-emphasis,
> rather they call for
> >>>>> de-emphasis. The effect is the same - the transitions are
> sent larger than
> >>>>> subsequent bits; but it is achieved by using the nominal
> level for the
> >>>>> first bit
> >>>>> after a transition and a smaller level for all subsequent
> bits. This makes
> >>>>> a nice
> >>>>> but smaller eye.
> >>>>>
> >>>>> --- Joe S.
> >>>>>
> >>>>>
> >>>>> Adiu wrote:
> >>>>>
> >>>>>
> >>>>>> Hello, Everyone
> >>>>>>
> >>>>>> What's pre-emphasis and de-emphasis?
> >>>>>> I can get the following definitions from Google:
> >>>>>>
> >>>>>> Pre-emphasis: " Improving the signal to noise ratio by
> increasing the magnitude of higher frequency signals with respect
> to lower frequency signals"
> >>>>>> De-emphasis: " Improving the signal to noise ratio by
> decreasing the magnitude of higher frequency signals with respect
> to lower frequency signals"
> >>>>>>
> >>>>>> There is not problem to understand the above definitions.
> However, I have difficulities in the following concerns:
> >>>>>> 1. is pre-emphasis always at the transmitter?
> >>>>>> 2. is de-emphasis always at the receiver?
> >>>>>> 3. what's difference between de-emphasis and equalization?
> >>>>>> 4. I have not problems to draw the pre-emphasis pulse
> waveforms with respect to a normal waveform. However, I am not
> quite sure of the de-emphasis pulse waveforms. The attached figure
> shows a simple example. Could someone confirms for me if the
> waveforms are draw correctly?
> >>>>>>
> >>>>>> any comments are appreciated.
> >>>>>>
> >>>>>> best regards,
> >>>>>> adiu
> >>>>>>
> >>>>>>
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