Digital Signal Processing Reference
In-Depth Information
4
3
2
1
0
-1
-2
-3
-4
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
850
900
950
ms
5,0
2,5
Distance corresponds to 1,4 r ad
(u
out
ahead u
in
)
0,0
Distance corresponds to 3,14 rad
-2,5
-5,0
0.0
2.5
5.0
7.5
10.0
12.5
15.0
17.5
20.0
22.5
ms
Illustration 103:
Function generator and oscilloscope
By means of a traditional function generator and oscilloscope it is possible - with time-consuming
measurement, reporting, evaluation (using a pocket calculator) and a graph of the curves - to determine
the frequency response according to the amplitude (
Û
out
/
Û
in
) and phase (
Δϕ
ϕ
out
-
ϕ
in
). Computer-
=
aided processes deal with this in fractions of a second.
The Illustrations betray two tricks for establishing the frequency response. The top representation suggests
that the amplitude curve depending on the frequency can be registered very quickly without constantly
switching the time base of the oscilloscope if the time base chosen is big enough. The (sinusoidal) input
signal and the output signal appear as “bars” the level of which can be easily read. The precision of the
phase curve can be maximised whereby for each measured frequency by means of the time base regulator
- usually a knob on or next to the time base switch - exactly one period half of
u
in
is presented over the
entire scale. By means of the calculation using the rule of three the phase shift can easily be calculated. As
a result of
Δϕ
ϕ
out
-
ϕ
in
and
ϕ
n
= 0
in the above situation this results in
Δϕ
=
=
1.4 rad or 81º (
u
out
rushes ahead).
