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# Why is the Noise Factor that I've counted inconsistent with the result of Pnoise?

Last post Mon, Feb 20 2012 10:36 PM by xxgeneral. 2 replies.
 Started by xxgeneral 16 Feb 2012 06:11 AM. Topic has 2 replies and 3419 views
• #### Thu, Feb 16 2012 6:11 AM

• xxgeneral
• Joined on Thu, Jan 26 2012
• Nanjing, Jiangsu
• Posts 4
• Points 65
Why is the Noise Factor that I've counted inconsistent with the result of Pnoise?
 Hi everyone,I've simulated the noise factor of Mixer ne600p in rfExamples library with PSS+Pnoise. With the Noise Summary printed, I calculated the Noise Factor, which is (total noise at output - load noise at output)/(source noise at output), then Noise Figure can be abtained with 10*lg(Noise Factor). However, my result is very different from the Noise Figure of Pnoise.######################################################## Noise Summary:-----------------------------------------------------------------------------------------Device    Param             Noise Contribution    % Of Total/rif           rn                5.70677e-19           23.13     IF_OUTPUT_Port/q57        rb                2.86098e-19           11.60     /rf            rn                2.74587e-19           11.13     RF_INPUT_Port/q56        rb                2.71557e-19           11.01     /r45         rn                1.60586e-19           6.51      /q57        ic                1.54208e-19           6.25      /q56        ic                1.1156e-19            4.52      /rl1         rn                1.03425e-19           4.19      /r44        rn                8.357e-20             3.39      /r46        rn                7.25826e-20           2.94      /q56        ib                5.65173e-20           2.29      /q58b     rb                5.51435e-20           2.23      /q58a     rb                5.51435e-20           2.23      /lo          rn                4.66997e-20           1.89      /q58a     ic                4.14535e-20           1.68      /q58b     ic                4.14535e-20           1.68      /q58b     ib                1.98622e-20           0.81      /q58a     ib                1.98622e-20           0.81      /q56      re                1.28295e-20           0.52      /q57      re                1.27064e-20           0.51      /q57      ib                7.93188e-21           0.32      /q58b     re                3.43834e-21           0.14      /q58a     re                3.43834e-21           0.14      /q58a     rc                9.14375e-22           0.04      /q58b     rc                9.14375e-22           0.04      /q57      rc                9.88927e-23           0.00      /q56      fn                4.43245e-23           0.00      /q56      rc                1.67595e-23           0.00      /q58b     fn                3.9707e-24            0.00      /q58a     fn                3.9707e-24            0.00      /q57      fn                1.26023e-24           0.00      /rl1      fn                0                     0.00      /rif      ext_file_noise    0                     0.00      /rf       ext_file_noise    0                     0.00      /r46      fn                0                     0.00      /r45      fn                0                     0.00      /r44      fn                0                     0.00      /lo       ext_file_noise    0                     0.00      /lm       fn                0                     0.00      /lm       rn                0                     0.00      /ldc      fn                0                     0.00      /ldc      rn                0                     0.00      /L1       fn                0                     0.00      /L1       rn                0                     0.00      /L0       fn                0                     0.00      /L0       rn                0                     0.00      Spot Noise Summary (in V^2/Hz) at 80M Hz Sorted By Noise ContributorsTotal Summarized Noise = 2.46733e-18Total Input Referred Noise = 8.63267e-18The above noise summary info is for pnoise data-----------------------------------------------------------------------------------------Total Noise at Output: No^2 = 2.46733e-18 V^2/HzLoad Noise at Output: Nl^2 = 5.70677e-19 V^2/HzSource Noise at Output: Ns^2 =  2.74587e-19 V^2/HzNoise Factor: N = (No^2 - Nl^2)/(Ns^2) = 6.90729 -----------------------------------------------------------------------------------------However, according to the Noise Factor curve of Pnoise, noise factor @80MHz is 43.11, which is very larger than 6.90729.######################################################## There must be something wrong. Anyone can help me?Thanks in advance!
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• Post Points: 20
• #### Thu, Feb 16 2012 6:21 AM

Re: Why is the Noise Factor that I've counted inconsistent with the result of Pnoise?
 See worked example of single and double sideband noise figure in a mixer. Your mistake (from a very quick glance) is that for the denominator you are using the total output noise from the input source, rather than the output noise from the input source from the passband only (i.e. the reference sideband). Otherwise the resulting noise figure is not the ratio of the signal to noise at the input to the signal to noise at the output.Anyway, it's covered in more detail in my solution linked to above.Regards,Andrew.
• Post Points: 20
• #### Mon, Feb 20 2012 10:36 PM

• xxgeneral
• Joined on Thu, Jan 26 2012
• Nanjing, Jiangsu
• Posts 4
• Points 65
Re: Why is the Noise Factor that I've counted inconsistent with the result of Pnoise?
 It's a great help. Thank you Andrew.
• Post Points: 5
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 Started by xxgeneral at 16 Feb 2012 06:11 AM. Topic has 2 replies.