Tektronix 434, Инструкция по эксплуатации

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C irc u it D e s c rip tio n —43 4
F ig . 3 -8 . T r ig g e r P i c k o f f a n d G e n e r a t o r d e t a ile d b lo c k d ia g ra m .
External trigger signals applied to the E XT T R IG in p u t
co n n e cto r can be used to trigger the Sweep Generator in
the E X T TR 1G mode o f o p e ra tio n . In p u t resistance at DC is
a bout one megohm paralleled b y a b o u t 100 picofarads
(about 70 picofarads w hen E X T A T T E N sw itch S70 is in
the 1:10 p o s itio n ). S etting the E XT A T T E N sw itch to the
1 :1 0 p o sitio n attenuates the in p u t signal by a fa c to r o f 10
to provide more L E V E L c o n tro l range, w h ile m aintaining
the one megohm in p u t resistance characteristic.
Trigger Coupling
The T R IG G E R C O U P LIN G switches S74, S 75A, and
S75B o ffe r a means o f accepting or rejecting certain
com ponents o f the trigger signal. In the AC and LF REJ
mode o f trigger co u p lin g , the DC co m ponent o f the trigger
signal is blocked by co upling capacitor C72 o r C74.
Frequency com ponents below a b o u t 60 hertz are a tte n u ­
ated w hen using AC coupling and below about 50 k ilo h e rtz
w h e n using LF REJ co u p lin g . The higher-frequency
com ponents o f the trigger signal are passed w ith o u t
a tte n u a tio n .
In the HF REJ mode o f trigger coupling, the trigger
signal is DC coupled to the in p u t if the AC and LF REJ
p u s h b u tt o n s are n o t also depressed. H igh-frequency
com ponents o f the trigger signal (above about 50 k ilo h e rtz )
are attenuated, w h ile the low er-frequency com ponents are
passed w ith o u t a tte n u a tio n . The DC mode o f trigger
c o u p lin g passes all signals fro m DC to 25 megahertz.
In p u t Source Follow er
The In p u t Source F o llo w e r, Q 6 0 5 A , provides a high
in p u t impedance fo r the trigger signal. It also provides
isolation between the Trigger Generator c irc u it and the
trigger signal source. D iode CR603 pro te cts Q 605A if an
excessive negative in p u t voltage is applied to the E X T T R IG
in p u t connector. The o u tp u t at the anode o f V R 6 0 5 is
connected to e m itte r fo llo w e r stage Q 610. Q 6 058 is a
rela tive ly constant c u rre n t source fo r Q 6 0 5 A , and provides
tem perature com pensation o f Q 605A .
Slope Com parator
U 650D and U650E are connected as an em itter-coupled
diffe re n ce a m p lifie r (com parator) to provide selection o f
the slope and level at w hich the sweep is triggered. The
reference voltage fo r the com parator is provided by the
L E V E L c o n tro l R60B and the Trigger Level Centering
3-11