[SI-LIST] Re: What's different between Pre-emphasis and De-emphasis?
- From: "Istvan NOVAK" <istvan.novak@xxxxxxxxxxxxxxxx>
- To: "lei luo" <lluo3@xxxxxxxxxxxxxx>, <jianhaw.tw@xxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 19 Oct 2004 21:59:43 -0400
Lei,
Yes, we agree, both increase the high-frequency content over the
low-frequency content. I guess the reason for this nomenclature
is that preemphasis in this context emphesizes the leading edge
and leaves the rest unchanged, while deemphasis by this definition
deemphesizes the trailing bits and leaves the leading edge unchanged.
Istvan
----- Original Message -----
From: "lei luo" <lluo3@xxxxxxxxxxxxxx>
To: <istvan.novak@xxxxxxxxxxxxxxxx>; <jianhaw.tw@xxxxxxxxxxxx>;
<si-list@xxxxxxxxxxxxx>
Cc: <jianhaw.tw@xxxxxxxxxxxx>
Sent: Tuesday, October 19, 2004 8:27 AM
Subject: Re: [SI-LIST] Re: What's different between Pre-emphasis and
De-emphasis?
> Istvan:
>
> > The other possibility to achieve the same affect is
> > instead of boosting the leading edge, to suppress everything
> > else. This is called deemphasis: you transmit the
> > leading edge with the nominal amplitude, but make
> > subsequent levels smaller.
>
> I think above process is still pre-emphasis since the high frequency
> components are emphasized relatively to the low frequency components.
>
> Lei
>
>
> ----- Original Message -----
> From: "Istvan NOVAK" <istvan.novak@xxxxxxxxxxxxxxxx>
> To: <jianhaw.tw@xxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
> Cc: <jianhaw.tw@xxxxxxxxxxxx>
> Sent: Tuesday, October 19, 2004 8:08 AM
> Subject: [SI-LIST] Re: What's different between Pre-emphasis and
> De-emphasis?
>
>
> > JH,
> >
> > While preemphasis and deemphasis were primarily used in
> > FM broadcasting and communications during the several
> > past decades, these terms got somewhat new meanings
> > in high-speed digital applications. Preemphasis means
> > that you boost high-frequency components, deemphasis
> > means the opposite: you suppress high-frequency components.
> >
> > In FM communications, the channel itself can be assumed to
> > be flat in frequency response. Preemphasis will cancel
> > with deemphasis, and this trick is used to suppress the
> > high-frequency boost of noise that occurs in the
> > demodulation process.
> >
> > In digital high-speed applications, the purpose of
> > preemphasis-deemphasis is to compensate for the
> > frequency dependent transfer function of traces
> > and/or cables, and usually they ARE NOT used in pairs,
> > because all what we want is to compensate for the
> > loss of high-frequency components.
> >
> > Preemphasis in high-speed digital applications means that
> > you boost the high-frequency components, usually by
> > amplifying somewhat the leading edge after a longer
> > period of no transitions. The problem with this approach
> > is that leading edges will require more voltage swing at
> > the driver, and the silicon may not like it.
> >
> > The other possibility to achieve the same affect is
> > instead of boosting the leading edge, to suppress everything
> > else. This is called deemphasis: you transmit the
> > leading edge with the nominal amplitude, but make
> > subsequent levels smaller.
> >
> > Again, as opposed to FM communications, you
> > want to do either preemphasis or deemphasis, not
> > both.
> >
> > Note that these are the simplest forms of channel
> > compensation, more sophistaced forms also exist.
> >
> >
> > Best regards,
> >
> > Istvan Novak
> > SUN Microsystems
> > ----- Original Message -----
> > From: "jianhaw.tw" <jianhaw.tw@xxxxxxxxxxxx>
> > To: <si-list@xxxxxxxxxxxxx>
> > Cc: <jianhaw.tw@xxxxxxxxxxxx>
> > Sent: Tuesday, October 19, 2004 2:33 AM
> > Subject: [SI-LIST] What's different between Pre-emphasis and
De-emphasis?
> >
> >
> >> Hi All,
> >> Just want to ask one simple question which already
> >> confused me a long time.
> >> What's different between Pre-emphasis and De-emphasis?
> >> Do they have different technology?
> >> Or can anyone indicate which are good documents?
> >>
> >> Thanks a lot.
> >>
> >> JH Oct.19,2004
> >
> >
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>
>
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