[SI-LIST] Re: clipped sine wave output
- From: "Ingraham, Andrew" <a.ingraham@xxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Tue, 13 May 2003 13:00:00 -0400
> Can you tell me the purpose and usages of a clock oscillator that generate
> a
> "clipped sine" wave output?
> Do you know an application where it's a requirement to have a "clipped
> sine"
> wave?
> If you can provide me a wave form of a clipped sine wave it will be very
> helpfull.
> Is it for EMC/EMI purposes?
This might be just a matter of semantics.
For digital logic, "square" waves work better than sine waves because the
fast edge rate makes them more immune to noise-induced jitter and skew, plus
most logic devices need a minimum input edge rate to behave correctly.
Whereas many RF devices need clean sine waves.
But at higher frequencies, the "square" waves don't look very square. They
look more like rounded trapezoids, or distorted (flattened) sine waves.
Perhaps someone called them "clipped sine waves" because that's what they
looked like (flat-ish tops and bottoms, but rounded edges).
Technically speaking, square waves do not exist except mathematically.
Neither do trapezoidal waves. So any oscillator that advertises "square" or
even "trapezoidal" outputs is technically not telling the truth. As if
anyone cares.
Most resonant oscillators actually produce sine waves internally, then
"square" them up to make binary outputs. I suppose you could clip them more
gracefully with a linear amp that clips, and end up with true clipped sine
waves that are somewhere between sine waves and trapezoidal/square waves.
Compared to sine waves, there is more hi-freq energy to radiate, but the
edge rates are faster. Compared to waves that are more "square" (which,
depending on clock frequency, might require super fast edges), the EMC/EMI
potential and SI problems would be reduced; however the edge rates could be
slow if the clock frequency is low. For a variable frequency oscillator
that actually generates a sine wave with clipping, its edge rate would
change with the frequency.
Regards,
Andy
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