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hbnoise noise figure

Franktgg

Hi,

I got some weird result when using hbnoise simulation. I am simulating a down-conversion mixer. I followed the cadence tutorial setting.

My simulation condition is hb:Flo =2.4GHz harmonic=50, hbnoise Fbb = 1M~10MHz, maximum sideband =1 (not the cause of quesiton)

My question is that Direct-plot generated "noise figure" is much high than the calcuated "noise summary" result.

I attached the result is the below figures, the noise figure from Direct-plot is ~9dB, but the noise summary is much lower than 9dB(/RF is port,/I0 is mixer).

I am wondering the way hbnoise calculate noise figure is different from noise summary?

  • The noise summary doesn't show the noise figure - so I'm confused as to what you're comparing with what?

    Andrew.

  • in reply to Andrew Beckett

    Hi Andrew,

    I am comparing with noise figure calculate from noise summary. NF = dB10(total output noise / output noise from source) =dB10(1.198e-14/4.18e-15)=4.57dB v.s direct plot 9dB.

  • in reply to Franktgg

    I'd be very surprised if the noise figure calculation is incorrect because this has been well proven over many years. It's computed by the ratio of the total output noise (less the noise from the load, if the load was specified as a probe on the noise analysis) divided by the noise from the source - bear in mind that the denominator is the noise from the source coming from the input frequency only. The noise contribution in the noise summary is the total noise from all input sidebands. So the denominator you're using from the noise summary is probably too large because of this.

    I just did a little experiment myself with a mixer, and if I did the calculation as you did, the noise figure was underestimated that way. If I turn on "saveallsidebands" on the hbnoise options form, and then plot the right noise contributor for the input port (from the results browser) and measure the value in the correct sidebands corresponding to the input frequency, and use that value as the denominator, the result I get is correct.

    So I suspect it's the fact that you've overlooked that /RF port contributor is not just from the input frequency in the noise summary.

    Andrew.

  • in reply to Andrew Beckett

    Hi Andrew,

    Thanks for your help. It's much clear now.

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