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104 Chapter 6
I/Q Analyzer
Frequency
Description Specifications Supplemental Information
Clipping-to-Noise Dynamic Range
a
a. This specification is defined to be the ratio of the clipping level (also known as “ADC Over Range”) to
the noise density. In decibel units, it can be defined as clipping_level [dBm] − noise_density [dBm/Hz];
the result has units of dBfs/Hz (fs is “full scale”).
Excluding residuals and spurious
responses
Clipping Level at Mixer Center frequency ≥ 20 MHz
IF Gain = Low −10 dBm −8 dBm (nominal)
IF Gain = High −20 dBm −17.5 dBm (nominal)
Noise Density at Mixer
at center frequency
b
b. The noise density depends on the input frequency. It is lowest for a broad range of input frequencies
near the center frequency, and these specifications apply there. The noise density can increase toward
the edges of the span. The effect is nominally well under 1 dB.
(DANL
c
+ IFGainEffect
d
) +
2.25 dB
e
c. The primary determining element in the noise density is the “Displayed Average Noise Level” on page
44.
d. DANL is specified with the IF Gain set to High, which is the best case for DANL but not for Clip-
ping-to-noise dynamic range. The core specifications “Displayed Average Noise Level” on page 44,
gives a line entry on the excess noise added by using IF Gain = Low, and a footnote explaining how to
combine the IF Gain noise with the DANL.
e. DANL is specified for log averaging, not power averaging, and thus is 2.51 dB lower than the true
noise density. It is also specified in the narrowest RBW, 1 Hz, which has a noise bandwidth slightly
wider than 1 Hz. These two effects together add up to 2.25 dB.
Example
f
f. As an example computation, consider this: For the case where DANL = −151 dBm in 1 Hz, IF Gain is
set to low, and the “Additional DANL” is −160 dBm, the total noise density computes to
−148.2 dBm/Hz and the Clipping-to-noise ratio for a −10 dBm clipping level is −138.2 dBfs/Hz.