Agilent Technologies N9010A - Manual (Page 41)

Chapter 1 41
Agilent EXA Signal Analyzer
Amplitude Accuracy and Range
Description Specifications Supplemental Information
Display Scale Fidelity
ab
Absolute Log-Linear Fidelity
(Relative to the reference condition:
−25 dBm input through 10 dB
attenuation, thus
−35 dBm at the input
mixer)
Input mixer level
c
Linearity
−80 dBm ≤ ML ≤ −10 dBm ±0.15 dB
ML <
−80 dBm ±0.25 dB
Relative Fidelity
d
Applies for mixer level
c
range from
−10 to −80 dBm, mechanical attenuator
only, preamp off, and dither on.
Sum of the following terms: Nominal
high level term Up to
±0.045 dB e
instability term Up to
±0.018 dB
slope term From equation
f
prefilter term Up to
±0.005 dB g
a. Supplemental information: The amplitude detection linearity specification applies at all levels below
−10 dBm at the input mixer; however, noise will reduce the accuracy of low level measurements. The
amplitude error due to noise is determined by the signal-to-noise ratio, S/N. If the S/N is large (20 dB or
better), the amplitude error due to noise can be estimated from the equation below, given for the
3-sigma (three standard deviations) level.
The errors due to S/N ratio can be further reduced by averaging results. For large S/N (20 dB or better),
the 3-sigma level can be reduced proportional to the square root of the number of averages taken.
b. The scale fidelity is warranted with ADC dither set to Medium. Dither increases the noise level by
nominally only 0.1 dB for the most sensitive case (preamp Off, best DANL frequencies). With dither
Off, scale fidelity for low level signals, around
−60 dBm or lower, will nominally degrade by 0.2 dB.
c. Mixer level = Input Level
− Input Attenuation
d. The relative fidelity is the error in the measured difference between two signal levels. It is so small in
many cases that it cannot be verified without being dominated by measurement uncertainty of the veri-
fication. Because of this verification difficulty, this specification gives nominal performance, based on
numbers that are as conservatively determined as those used in warranted specifications. We will con-
sider one example of the use of the error equation to compute the nominal performance.
Example: the accuracy of the relative level of a sideband around
−60 dBm, with a carrier at −5 dBm,
using attenuation = 10 dB, RBW = 3 kHz, evaluated with swept analysis. The high level term is evalu-
ated with P1 =
−15 dBm and P2 = −70 dBm at the mixer. This gives a maximum error within
±0.025 dB. The instability term is ±0.018 dB. The slope term evaluates to ±0.050 dB. The prefilter term
applies and evaluates to the limit of
±0.005 dB. The sum of all these terms is ±0.098 dB.
e. Errors at high mixer levels will nominally be well within the range of
±0.045 dB × {exp[(P1 −
Pref)/(8.69 dB)]
− exp[(P2 − Pref)/(8.69 dB)]} (exp is the natural exponent function, e x
). In this expres-
sion, P1 and P2 are the powers of the two signals, in decibel units, whose relative power is being mea-
sured. Pref is
−10 dBm (−10 dBm is the highest power for which linearity is specified). All these levels
are referred to the mixer level.
3
σ
3 20dB
( )
1 10 S N ⁄ 3dB + ( ) 20dB ⁄ ( ) – +
〈 〉
log =