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Message started by Julian18 on Dec 16th, 2007, 10:30pm

Title: Question about NF ieee and NF dsb
Post by Julian18 on Dec 16th, 2007, 10:30pm
Hi, there
   From spectre document, we can find the definition for Nsi & Nso:
      Nsi = noise at the output due to the image harmonic at the source
      Nso = noise at the output due to harmonics other than input at the source
but really I dont know what is the image harmonic at the source, what does the "image harmonic" mean? Also, which component at the source is not the input but the harmonics as the Nso definition says.

Thanks.

Title: Re: Question about NF ieee and NF dsb
Post by Ken Kundert on Dec 17th, 2007, 12:02am
Consider a high-side down conversion mixer at the input of a receiver. For the sake of the example, assume that the LO frequency is 1GHz and the input frequency is 1.2GHz and the output frequency is 200MHz. Well, because the mixer responds nonlinearly with respect to the LO, it is not only input signals at 1.2GHz that get converted to 200MHz at the output. Any signal at the input at ±k×1GHz+200MHz will also be converted to the output at 200MHz. In this example  k=1 represents the desired harmonic, k=-1 represents the image harmonic, and all k≠±1 are the other harmonics. In other words, noise at the output at 200MHz that comes from the input at 800MHz is Nsi and from the input at 1.8GHZ, 2.2GHz, 2.8GHz, 3.2GHz, etc is Nso.

-Ken

Title: Re: Question about NF ieee and NF dsb
Post by Julian18 on Dec 18th, 2007, 1:10am

Ken Kundert wrote on Dec 17th, 2007, 12:02am:
Consider a high-side down conversion mixer at the input of a receiver. For the sake of the example, assume that the LO frequency is 1GHz and the input frequency is 1.2GHz and the output frequency is 200MHz. Well, because the mixer responds nonlinearly with respect to the LO, it is not only input signals at 1.2GHz that get converted to 200MHz at the output. Any signal at the input at ±k×1GHz+200MHz will also be converted to the output at 200MHz. In this example  k=1 represents the desired harmonic, k=-1 represents the image harmonic, and all k≠±1 are the other harmonics. In other words, noise at the output at 200MHz that comes from the input at 800MHz is Nsi and from the input at 1.8GHZ, 2.2GHz, 2.8GHz, 3.2GHz, etc is Nso.

-Ken


Thanks Ken,
I think I get what you mean, but why do you use ±k×1GHz+200MHz instead of k×1GHz±200MHz to represent the harmonics? Using the former form get the frequency < 0

Title: Re: Question about NF ieee and NF dsb
Post by Ken Kundert on Dec 18th, 2007, 7:04pm
Yes, those are the lower sidebands.

-Ken

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