Agilent Technologies 22A Specifiche Scaricare il pdf (Pagina 73)

We can construct a similar line for third-order distortion. For example,

a data sheet might say third-order distortion is –85 dBc for a level of –30 dBm

at this mixer. Again, this is our starting point, and we would plot the point

shown in Figure 6-2. If we now drop the level at the mixer to –40 dBm, what

happens? Referring again to Figure 6-1, we see that both third-harmonic

distortion and third-order intermodulation distortion fall by 3 dB for every

dB that the fundamental tone or tones fall. Again it is the difference that

is important. If the level at the mixer changes from –30 to –40 dBm, the

difference between fundamental tone or tones and internally generated

distortion changes by 20 dB. So the internal distortion is –105 dBc. These

two points fall on a line having a slope of 2, giving us the third-order

performance for any level at the mixer.

–60 –50 –40 –30 –20 –10 +100

–90

–80

–70

–60

–50

–40

–30

–20

–10

(

)

Mixer level (dBm)

(dBc)

Maximum 2nd order

dynamic range

Maximum 3rd order

dynamic range

Optimum

mixer levels

–100

TOI

SHI

Figure 6-2. Dynamic range versus distortion and noise

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Agilent Technologies 22A Specifiche Pagina 73