[SI-LIST] Re: Oscilloscope bandwidth and Non_Monotonic
- From: Surjendra Goswami <goswamisurjendra@xxxxxxxxx>
- To: balaseven@xxxxxxxxx
- Date: Sat, 22 Nov 2014 00:17:06 +0530
Bala,
You can visualize the non-monotonic waveform as a higher frequency signal
riding on top of your clock signal. In case this signal frequency content
is higher than the bandwidth of your scope then you might not see this
non-monotonicity.
You can try to see this effect by combining two signals using a power
combiner and then try to probe the output on the scope. One input of the
combiner would be your clock and another would be a sine wave of varying
frequency with amplitude quite low compared to your original clock signal.
As you control the frequency of this other sine wave, you would see that
this is detected on the scope (riding on top of the clock signal) till
frequencies what you calculated in your bandwidth calculation earlier.
Beyond the bandwidth the sine-wave is expected to progressively attenuate
in amplitude.
Regards
Surjendra
On Fri, Nov 21, 2014 at 1:04 AM, <austin@xxxxxxxxxx> wrote:
> Hi Bala,
>
> If the clock is driving an input with high capacitance such as an FPGA,
> there will be a negative reflection seen at the input pin. It may be
> monotonic at the die.
>
> Austin
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On
> Behalf Of bala
> Sent: Thursday, November 20, 2014 7:31 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Oscilloscope bandwidth and Non_Monotonic
>
>
> Hi All,
> I am measuring 125MHZ,1.2ns rise time clock with Tek's scope.
>
> When i measure clock with 5G Bandwidth i see non monotonic edges,when i
> measure the same clock with 500MHZ and 1GHZ,clock was clean.
>
> Here is the formula i use whenever assess clock signals,
>
> Fknee=0.5/rise=0.5/1.2ns=416MHZ
>
> Required bandwidth for maximum accuracy=1.9*419=800MHZ.
>
> Since required bandwidth is 800MHZ ,can i consider waveform with 1G as
> precise waveform.?
>
> Why non-monotonic appears at high BW?
>
> --
> bala
>
>
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