Specifications

The lowpass impulse response displays the location of discontinuities
as well as information useful in determining the impedance (R, L, or
C) of each discontinuity.
The impulse response is a peak that goes positive for R>Z
0
and
negative for R<Z
0
. The height of the response is equal to the reflection
coefficient
r=
-
+
RZ
RZ
0
0
The impulse response for a shunt capacitance is a
negative-then-positive peak and for a series inductance is a
positive-then-negative peak (Figure 8-1).
An example of using impulse response is circuit impedance analysis.
With an impulse response, we can observe the circuit response of a
passive device, such as a multi-element step attenuator (Figure 8-2),
and make final, realtime adjustments during the test.
In the above example, the connectors at each end have been gated out
(page 8-13), which lets you better observe the internal circuit response.
Each displayed marker has been manually set to the peak of the
response at each adjustable circuit element. In this way, the data
display lets you make the adjustment in realtime, while the marker
menu shows the magnitude of the response at each marker.
The lowpass-step response displays the location of discontinuities as
well as information useful in determining the impedance (R, L, or C) of
each discontinuity. If you are familiar with time-domain reflectometry
TIME DOMAIN TIME
MEASUREMENTS DOMAIN
8-4 MS462XX OM
LOWPASS IMPULSE RESPONSE
l
Location of Discontinuities
l
Information on Type of Discontinu
-
ities
CIRCUIT ELEMENTS
R>Z
O
SHUNT C
SERIES L
IMPEDANCE
O
R<Z
Lowpass Impulse Response
11
S REAL
Figure 8-1. Lowpass Impulse
Response
0.000ps
700.000ps
S11 FORWARD REFLECTION
LINEAR MAG. REF=5.000mU 7.000mU/DIV
LP w/G
6 152.514 ps
27.534 mU
2 465.363 ps
15.624 mU
3 375.419 ps
15.020 mU
4 293.296 ps
9.593 mU
5 195.531 ps
11.624 mU
MARKER TO MAX
MARKER TO MIN
MARKER 1
512.291 ps
36.890 mU
CH 1 - S11
00.000 ps diy
STEP ATTENUATOR
1
4
6
2
3
5
Figure 8-2. Example of Lowpass Impulse Response