[SI-LIST] Re: what's de-emphasis
- From: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>
- To: "Istvan Novak" <istvan.novak@xxxxxxx>, "Adiu" <adiu_panli@xxxxxxxxx>
- Date: Mon, 2 Nov 2009 10:23:40 -0800
Istvan,
Well put. For accuracy, the first is preemphasis.
Lee
> [Original Message]
> From: Istvan Novak <istvan.novak@xxxxxxx>
> To: Adiu <adiu_panli@xxxxxxxxx>
> Cc: LY <long.0.yang@xxxxxxxxx>; Bill Wurst <billw@xxxxxxxxxxx>; prasad
<hariprasad.palli@xxxxxxxxx>; <Joseph.Schachner@xxxxxxxxxx>;
<si-list@xxxxxxxxxxxxx>
> Date: 11/2/2009 5:45:58 AM
> Subject: [SI-LIST] Re: what's de-emphasis
>
> 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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