NF FRA51615, Instruction Manual

Page: 187 / 306

5.6 Marker operations
5
-
25
FRA 51615
(Example 2) : Automatic search for the phase margin of a negative feedback loop
In a feedback loop, the frequency for which the pass gain is 0 dB is the loop bandwidth. The phase at
that frequency is the phase margin.
•
Set [SEARCH VALUE Y1] to 0.0.
•
Set [AUTO SEARCH] to [Y1] .
When the sweep measurement is completed, the marker is automatically moved to the frequency for
which the gain is closest to 0 dB. The frequency and phase of the marker position correspond to the
loop and phase margin.
(Example 3): Measuring the self-resonant frequency of an inductor
Set the display units to IMPEDANCE and measure the impedance characteristic of the inductor DUT
(set the Y1 axis to Z and set the Y2 axis to θ).
•
Set
[AUTO SEARCH]
to
[Y1 PEAK]
.
When the sweep is completed, the marker moves to the maximum Z value. The marker frequency is
the self-resonant frequency. The resonance frequency may be the frequency for which the phase is 0°.
In that case, set the value is as shown below.
•
Set
[SEARCH VALUE Y2]
to 0.0.
•
Set
[AUTO SEARCH]
to
[Y2]
.
X (Frequency)
Y1 (Gain)
0 dB
Y2 (
θ)
Phase
Margin
0 deg
＊
＊
Loop
Bandwidth
X (Frequency)
Y1 (Z)
Y2 (
θ)
Y1 PEAK
0 deg
＊
＊
Resonance
Frequency
VALUE Y2=0 deg