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[SOLVED] Very basic question about Spectrum Analyzer.

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palmeiras

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Hello guys,

I’m designing a simple ring oscillator. I’m going to measure the phase noise and the output voltage swing of this oscillator.
Can I use the spectrum analyzer to see and measure the output voltage swing? Can I see time-domain signal? (Or I'll be able to see only the frequency domain?).

Thanks very much
 

Dear palmeiras
Hi
Of course you can use an spectrum analyzer to measure it's out put voltage and frequency , and variation in frequency .
Best Wishes
Goldsmith
 
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palmeiras said:
Hello guys,
I’m designing a simple ring oscillator. I’m going to measure the phase noise and the output voltage swing of this oscillator.
Can I use the spectrum analyzer to see and measure the output voltage swing? Can I see time-domain signal? (Or I'll be able to see only the frequency domain?).

Thanks very much
Click to expand...

Palmeiras,
with a spectrum analyzer you are able to measure the spectrum of a signal - surprise?
That means, yu can measure the magnitudes and frequencies of the oscillator signal (main component and harmonics), but you cannot see the signal in the time domain.
 
Lvw,
I have never had access to work with spectrum analyzer. So, can’t I see the output in time domain?
What did goldsmith mean with its answer?!
Thanks very much Lvw

- - - Updated - - -

Lvw,
Please, one more question.
Could I connect the output of my ring-oscillator directly to the spectrum analyzer without dc-blocking cap? (the output of ring-oscillator is shown in the attached figure).
I know that spectrum analyzer does not allow for dc voltages. But I could connect a square waveform to it, couldn’t I?
Thanks very much,


 

Spectrum analysers will normally show you "power level"s, normally dbM, (0 dBm is 1mW) which can be referenced to voltage-levels if you know the line impedance... -3db means half the power (-3dBm is 1/2mW), but power is (V^2)/R so 1/2ing the power is reducing the voltage to 0.707times the value...

Your wave will produce many separate peaks, the largest at the base-wave frequency, and 2/3/4/5/etc harmonics at progressively lower levels...... ( .|..'..:.. is the closes graphic!)
NEAL

There's normall a DC blocking cap in the instrument but won't hurt to put your own in, a large-ish (10uf ish) cap'll make sure you get plenty of signal,
Cool
NEAL
 

Hi palmeiras
did you see FFT in pspice ? the spectrum analyzer will show you things such as that ( but more advanced that ) .
 
There's normall a DC blocking cap in the instrument but won't hurt to put your own in, a large-ish (10uf ish) cap'll make sure you get plenty of signal.
Click to expand...
Only SA with restricted frequency range have possibly blocking capacitors. Instruments with > some GHz bandwidth rarely have. But the ability to deal with DC input voltages (or AC with offset, as in your case) should be clearly written on the instruments front panel.

The other point is that SA have always 50 ohm input impedance, most likely not a suitable load for your ring oscillator circuit. You would usually place a voltage divider, e.g. 10:1, in other words a simple 450 ohm series resistor.
 
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