discrepancy between spectrum peak value and calculator value in Direct Plot Form after hb simulation

What is your frequency set up in the hb analysis? I suspect you've got commensurate frequencies and so harmonics end up in the same place, but would be good to understand so I can explain what's going on.

Andrew

Dear aidenK,

I might add a few of comments if I may...

As Andrew noted, I am wondering what you set your frequency to in the harmonic balance analysis. If I examine your plot as shown in my first attachment, it appears your harmonic balance analysis may have been performed with a frequency of 2 MHz. Please refer to my questions and comments on the annotated versions of your plots as well as my example that may explain what you are observing in your spectral and frequency plots.

Please correct any of my thoughts and comments...

Shawn

Thanks for that Shawn. Since the results were from a multi-tone simulation (based on the direct plot form showing hb_mt), my guess is that the frequencies are such that harmonic combinations end up at the same frequency (1MHz) and so there are two points at the same frequency. Spectre RF produces both the individual combinations (indexed by harmonic) and the overall total (index by frequency). For one you need to use harmonic() to find the value (because it's indexed by harmonic) and for the other you need to use value(). If you use value on the indexed-by-harmonic result, then it can get confused because the data is not necessarily monotonically increasing by frequency.

Hence my request to understand the simulation setup, as then I (or anyone else) can give a precise explanation.

So your explanation looks likely to be close to the reason - although I think the frequencies may be indentical rather that closely-spaced. Let's see!

Regards,

Andrew.

Hi all, 

Thank you guys for answers. 

Actually, this is RF Rx simulation with 3 tones in HB. 

flo=2427MHz, frf1=2429MHz, frpl=1MHz and each harmonics are set 20,1,1 as above.

Therefore, only tones at nflo+mfrf1+kfrpl, n={-20,-19,...0,...19,20}, m=[-1,0,1}, k={-1,0,1} can be generated after simulation. 

At the Rx output, tone at 2MHz is a signal (2429M-2427M) and tones at 1MHz and 3MHz are spurs generated by non-linearity of Rx.

I think that there are two different mechanism to generate tone 1MHz, frpl and frf1-frpl-flo. 

If it is correct, can a plot from "spectrum" have two different values and a plot from "frequency" have complex-number added value?

Dear aidenK,

aidenK said:

Actually, this is RF Rx simulation with 3 tones in HB. 

Thank you for providing a bit more detail! I, for one anyway, cannot make out any text in your dialog box as the resolution is not sufficient. Perhaps if you include the context of the command from the input.scs file (or an image with higher resolution), it might help. Nevertheless, I understand that your LO freuqency is 2.427 MHz with the two interfering frequencies at 2.429 MHz and 1 MHz.

aidenK said:

I think that there are two different mechanism to generate tone 1MHz, frpl and frf1-frpl-flo. 

Yes. The non-linearities of a general amplifier will produce a number of frequency components near 1 MHz. The note below outlines a few and their origin if that helps.

aidenK said:

If it is correct, can a plot from "spectrum" have two different values and a plot from "frequency" have complex-number added value?

As Andrew noted the harmonic() function is indexed by the harmonic number and as Andrew also noted

Andrew Beckett said:

If you use value on the indexed-by-harmonic result, then it can get confused because the data is not necessarily monotonically increasing by frequency.

Hence, I suspect this is the source of your result. Does this help aidenK?

Shawn