Tektronix TYPE 109 Instruction Manual page 16

Applications— Type 109
F ig . 3 - 4 . W a v e fo rm o b ta in e d w h en a
In Fig. 3-4 the ratio of V0 to V , is approximately 1.75.
Using this in the above formula gives the correct impedance
of 125 ohms used to produce the waveform.
It is essential in applications of the type described here
that no shorts, terminations, terminated adapters, or attenu­
ators having low shunt resistance to ground are used in
the charge line of the Type 109. If devices such as these
are used, they will prevent the charge line from charging to
the correct voltage and will thereby prevent the Type 109
from producing an output waveform. Where it is necessary
to match one type of connector to another, low-loss un­
terminated adapters should be used.
est, I '
(If component under testN I '
is connected here
i Y
place of cable under
test, ground other end p
ß
of component to 50 i
cable shield.) I
,__ i
From
Q
6 6.7
Type 109 ( A
A A A ----
U
50 OUTPUT V7
Connector
100 Q, 1%
Vt
w
Dividing Pad
All Resistors: 1 % ,
F ig . 3 - 5 . T h re e -w a y d iv id in g p a d
p e d an ce b y re fle ctio n .
As an alternate method, you can construct a dividing
pad such as the one shown in Fig. 3-5. This pad overcomes
a disadvantage of the previous method. With this pad you
can connect low-shunt resistance components or devices to
3-4
_________________P O R I IO N C UE T O 1 25 O JJN IE _
— H
V * -1
— w
V o
" n r
1 J 1 1
V
;
Equivalent Sweep Rate: 5 nsec/cm
(Sampling) Oscilloscope: Type 661
section o f n o m in al 125 -o h m c a b le is connected a s p a rt of the ch arg e lin e fo r the T yp e 1 0 9 .
(Cable-under-test cen­
ter conductor can be left
open or shorted to coax
X A
shield.)
Cable or Component
under test
?-T
50 S3 cable (Used as a
reference impedance)
66.7 Q
, \ To 50
----W v
Input of
Oscilloscope
lOOfi, 1%
Vi
w
^
Vi
watt
test circu it fo r m e asu rin g im­
u
V v
, V
mJ
iii r
AWA
V
: O N D i \R Y
s e c
: p n i f "INK
p f f
— V
the 50 n cable (used as the reference) and determine their
characteristics. If this pad is constructed and used, the
formula for determining the impedance is as follows:
where: Z = the unknown impedance.
V0 = the peak amplitude produced by the
50 Q reference impedance.
Vx = the peak amplitude at the time of
the reflection.
Using the Type 109 With a Conventional Oscil­
loscope
The Type 109 can be used with conventional oscilloscopes
in much the same manner as with sampling oscilloscopes
that have internal triggering capabilities. Fig. 3-6 shows the
connections required.
must have an internal delay line if the signal from the de­
vice is fast-rise non-repetitive or has a low duty cycle.
This setup is useful where the frequency response of the
device falls within the bandwidth limitations of the vertical
amplifier system of the oscilloscope.
the applied signal is the method that must be used to trig­
ger the sweep. This method of triggering is convenient
since no external triggering connections are required.
A second system is shown in Fig. 3-7. Here the device
under test, besides being pulsed by the Type 109, is able
to provide external triggers to the oscilloscope. It is there­
by possible to observe the shaping and amplification of a
signal in the circuits of the device without resetting the
oscilloscope triggering controls for each observation. If the
external triggering signal is derived from the waveform
at the input circuit of the device under test, the time re­
lationship and phase between the output and input wave-
The oscilloscope used in this setup
Internal triggering on
O