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Dear Frieds,
I am facing a problem while finding SNR of a adc output. I am givin
sinusoidal wave at the input amd getting sinusoidal wave with harmonic
and noise at output. Now, to calculate power for my fundamental frequenc
and noise, I am using DFT. But as I am changing the number of samples,
am getting different-different SNR. Here, I am also considering spectru
leakage in FFT. So, as my fundamental frequence is 122070312.5H
(122.07MHz) and I am sampling it with 25GHz, I am taking number of sample
1024 and 2048. I am getting 5db SNR with 1024 samples and 14db SNR wit
2048 samples. Please help me find where am I going wrong ?
Thanks

On Feb 8, 6:17 am, "sunil_ic" <sunil...@gmail.com> wrote:
> Dear Frieds,
> I am facing a problem while finding SNR of a adc output. I am giving
> sinusoidal wave at the input amd getting sinusoidal wave with harmonics
> and noise at output. Now, to calculate power for my fundamental frequency
> and noise, I am using DFT. But as I am changing the number of samples, I
> am getting different-different SNR. Here, I am also considering spectrum
> leakage in FFT. So, as my fundamental frequence is 122070312.5Hz
> (122.07MHz) and I am sampling it with 25GHz, I am taking number of samples
> 1024 and 2048. I am getting 5db SNR with 1024 samples and 14db SNR with
> 2048 samples. Please help me find where am I going wrong ?
> Thanks

25 GHz ???????

On Fri, 8 Feb 2008 03:50:32 -0800 (PST), John <[email protected]>
wrote:

>On Feb 8, 6:17 am, "sunil_ic" <sunil...@gmail.com> wrote:
>> Dear Frieds,
>> I am facing a problem while finding SNR of a adc output. I am giving
>> sinusoidal wave at the input amd getting sinusoidal wave with harmonics
>> and noise at output. Now, to calculate power for my fundamental frequency
>> and noise, I am using DFT. But as I am changing the number of samples, I
>> am getting different-different SNR. Here, I am also considering spectrum
>> leakage in FFT. So, as my fundamental frequence is 122070312.5Hz
>> (122.07MHz) and I am sampling it with 25GHz, I am taking number of samples
>> 1024 and 2048. I am getting 5db SNR with 1024 samples and 14db SNR with
>> 2048 samples. Please help me find where am I going wrong ?
>> Thanks
>
>25 GHz ???????

Not infeasable on a newer oscilloscope.

Regards,
Allan

>On Fri, 8 Feb 2008 03:50:32 -0800 (PST), John <[email protected]>
>wrote:
>
>>On Feb 8, 6:17 am, "sunil_ic" <sunil...@gmail.com> wrote:
>>> Dear Frieds,
>>> I am facing a problem while finding SNR of a adc output. I am giving
>>> sinusoidal wave at the input amd getting sinusoidal wave wit
harmonics
>>> and noise at output. Now, to calculate power for my fundamenta
frequency
>>> and noise, I am using DFT. But as I am changing the number of samples
I
>>> am getting different-different SNR. Here, I am also considerin
spectrum
>>> leakage in FFT. So, as my fundamental frequence is 122070312.5Hz
>>> (122.07MHz) and I am sampling it with 25GHz, I am taking number o
samples
>>> 1024 and 2048. I am getting 5db SNR with 1024 samples and 14db SN
with
>>> 2048 samples. Please help me find where am I going wrong ?
>>> Thanks
>>
>>25 GHz ???????
>
>Not infeasable on a newer oscilloscope.
>
>Regards,
>Allan
>

Its not Oscilloscope setup. I am doing matlab simulation.

On Feb 12, 7:10*am, "sunil_ic" <sunil...@gmail.com> wrote:
> >On Fri, 8 Feb 2008 03:50:32 -0800 (PST), John <sampson...@gmail.com>
> >wrote:
>
> >>On Feb 8, 6:17 am, "sunil_ic" <sunil...@gmail.com> wrote:
> >>> Dear Frieds,
> >>> I am facing a problem while finding SNR of a adc output. I am giving
> >>> sinusoidal wave at the input amd getting sinusoidal wave with
> harmonics
> >>> and noise at output. Now, to calculate power for my fundamental
> frequency
> >>> and noise, I am using DFT. But as I am changing the number of samples,
> I
> >>> am getting different-different SNR. Here, I am also considering
> spectrum
> >>> leakage in FFT. So, as my fundamental frequence is 122070312.5Hz
> >>> (122.07MHz) and I am sampling it with 25GHz, I am taking number of
> samples
> >>> 1024 and 2048. I am getting 5db SNR with 1024 samples and 14db SNR
> with
> >>> 2048 samples. Please help me find where am I going wrong ?
> >>> Thanks
>
> >>25 GHz ???????
>
> >Not infeasable on a newer oscilloscope.
>
> >Regards,
> >Allan
>
> Its not Oscilloscope setup. I am doing matlab simulation.- Hide quoted text -
>
> - Show quoted text -

How are you calculating SNR?

Dirk

>On Feb 12, 7:10=A0am, "sunil_ic" <sunil...@gmail.com> wrote:
>> >On Fri, 8 Feb 2008 03:50:32 -0800 (PST), John <sampson...@gmail.com>
>> >wrote:
>>
>> >>On Feb 8, 6:17 am, "sunil_ic" <sunil...@gmail.com> wrote:
>> >>> Dear Frieds,
>> >>> I am facing a problem while finding SNR of a adc output. I a
giving
>> >>> sinusoidal wave at the input amd getting sinusoidal wave with
>> harmonics
>> >>> and noise at output. Now, to calculate power for my fundamental
>> frequency
>> >>> and noise, I am using DFT. But as I am changing the number o
samples,=
>
>> I
>> >>> am getting different-different SNR. Here, I am also considering
>> spectrum
>> >>> leakage in FFT. So, as my fundamental frequence is 122070312.5Hz
>> >>> (122.07MHz) and I am sampling it with 25GHz, I am taking number of
>> samples
>> >>> 1024 and 2048. I am getting 5db SNR with 1024 samples and 14db SNR
>> with
>> >>> 2048 samples. Please help me find where am I going wrong ?
>> >>> Thanks
>>
>> >>25 GHz ???????
>>
>> >Not infeasable on a newer oscilloscope.
>>
>> >Regards,
>> >Allan
>>
>> Its not Oscilloscope setup. I am doing matlab simulation.- Hide quote
tex=
>t -
>>
>> - Show quoted text -
>
>How are you calculating SNR?
>
>Dirk
>

Dear Dirk,
At 25GHz sample rate, I am doing 1024 point FFT at output from the ADC. S
my input signal (122070312.5Hz) will be at f5, 5th sample, in frequenc
domain (FFT of the output signal). So I calculated singal power by takin
square of the 5th sample. And rest all samples in the FFT are th
noise+harmonics. So I calculated noise power by integrating all samples
square.
Thanks

On 13 Feb, 05:05, "sunil_ic" <sunil...@gmail.com> wrote:
> >On Feb 12, 7:10=A0am, "sunil_ic" <sunil...@gmail.com> wrote:

> >How are you calculating SNR?
>
> >Dirk
>
> Dear Dirk,
> At 25GHz sample rate, I am doing 1024 point FFT at output from the ADC. So
> my input signal (122070312.5Hz) will be at f5, 5th sample, in frequency
> domain (FFT of the output signal). So I calculated singal power by taking
> square of the 5th sample. And rest all samples in the FFT are the
> noise+harmonics.

Seems reasonable.

> So I calculated noise power by integrating all samples'
> square.

Did you make sure to leave ouut the harmonic where the signal
is located?

Rune

>On 13 Feb, 05:05, "sunil_ic" <sunil...@gmail.com> wrote:
>> >On Feb 12, 7:10=A0am, "sunil_ic" <sunil...@gmail.com> wrote:
>
>> >How are you calculating SNR?
>>
>> >Dirk
>>
>> Dear Dirk,
>> At 25GHz sample rate, I am doing 1024 point FFT at output from the ADC
So
>> my input signal (122070312.5Hz) will be at f5, 5th sample, i
frequency
>> domain (FFT of the output signal). So I calculated singal power b
taking
>> square of the 5th sample. And rest all samples in the FFT are the
>> noise+harmonics.
>
>Seems reasonable.
>
>> So I calculated noise power by integrating all samples'
>> square.
>
>Did you make sure to leave ouut the harmonic where the signal
>is located?
>
>Rune
>
I am considering harmonics also as Noise. Is it true assumption ?

On 15 Feb, 09:10, "sunil_ic" <sunil...@gmail.com> wrote:
> I am considering harmonics also as Noise. Is it true assumption ?

Ah, I didn't read your original post carefully enough - you
actually measure the SNR of an ADC, right?

There are procedures for testing those sorts of things.
Check your ADC's data sheet (or with the manufacturer,
they might have a procedure), or read chapter 13.9.1 in

Lyons: Understanding DSP, 2nd ed., 2004.

Rune

sunil_ic wrote:
>> On 13 Feb, 05:05, "sunil_ic" <sunil...@gmail.com> wrote:
>>>> On Feb 12, 7:10=A0am, "sunil_ic" <sunil...@gmail.com> wrote:
>>>> How are you calculating SNR?
>>>> Dirk
>>> Dear Dirk,
>>> At 25GHz sample rate, I am doing 1024 point FFT at output from the ADC.
> So
>>> my input signal (122070312.5Hz) will be at f5, 5th sample, in
> frequency
>>> domain (FFT of the output signal). So I calculated singal power by
> taking
>>> square of the 5th sample. And rest all samples in the FFT are the
>>> noise+harmonics.
>> Seems reasonable.
>>
>>> So I calculated noise power by integrating all samples'
>>> square.
>> Did you make sure to leave ouut the harmonic where the signal
>> is located?
>>
>> Rune
>>
> I am considering harmonics also as Noise. Is it true assumption ?

Only in the sense that any unwanted signal could be loosely called
noise. In the same way, a tomato plant in a flower garden could be
called a weed.

Jerry
--
Engineering is the art of making what you want from things you can get.
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