Agilent Technologies 22A Specifiche Scaricare il pdf (Pagina 76)

The final factor in dynamic range is the phase noise on our spectrum analyzer

LO, and this affects only third-order distortion measurements. For example,

suppose we are making a two-tone, third-order distortion measurement on

an amplifier, and our test tones are separated by 10 kHz. The third-order

distortion components will also be separated from the test tones by 10 kHz.

For this measurement we might find ourselves using a 1 kHz resolution

bandwidth. Referring to Figure 6-3 and allowing for a 10 dB decrease in

the noise curve, we would find a maximum dynamic range of about 88 dB.

Suppose however, that our phase noise at a 10 kHz offset is only –80 dBc.

Then 80 dB becomes the ultimate limit of dynamic range for this measurement,

as shown in Figure 6-4.

In summary, the dynamic range of a spectrum analyzer is limited by three

factors: the distortion performance of the input mixer, the broadband noise

floor (sensitivity) of the system, and the phase noise of the local oscillator.

–60 –50 –40 –30 –20 –10 +100

–100

–110

–90

–80

–70

–60

–50

–40

–30

–20

–10

Mixer level (dBm)

(dBc)

Dynamic range

reduction due

to phase noise

Phase noise

(10 kHz offset)

Figure 6-4. Phase noise can limit third-order intermodulation tests

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Agilent Technologies 22A Specifiche Pagina 76