Tektronix FG 5010 User Manual

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Square - Wave
Buffer
The
Square
-
wave
Buffer
produces
the
actual
square
wave
that
is
selected for use
at the
FG
5010
output .
The
circuit
consists
of
line
receiver
U1200B ;
amplifiers
U1310A
and
U1310B
;
transistors
Q1216
,
Q1211 ,
Q1212 ,
Q1215 ,
Q1210
,
Q1213
,
Q1214
, and
Q1110
;
plus
related
circuits .
The
circuit
consists of
positive
and negative
current
sources , a driver , and a current switch .
Amplifier
U1310B ,
transistor
Q1216
,
and
related
compo
nents form the
positive current source for
the buffer . The
reference for
the
circuit is
R1322 and
VR1310 ,
which
sets
the voltage at the bottom of R1420 to +5.8 V. The divider
that
consists
of
R1314
,
R1313
,
and
adjustment
R1318
sets
the
current
level
for
the
negative
current
source .
Likewise ,
the
divider
consisting of
R1421 ,
R1420 ,
and
adjustment
R1422
sets
the
output
level
for
the
positive
current
source
.
The
voltage at the
noninverting input
of
U1310B , pin 5 ,
con
trols the
voltage
drop
across R1312
and thus the
current
through
Q1216
. This
current
is
supplied
to
differential
pair
Q1212
and
Q1215
,
part of the
output
stage
of the
buffer
.
Similarly , the voltage from the wiper arm of R1318 sets
the
current
through the
negative
current
source
,
which con
sists of amplifier U1310A , transistor Q1110 , and surround
ing
components . The voltage
at the
inverting input sets the
voltage across R1115 , and therefore the current through
Q1110
.
The
collector of
Q1110
connects to
differential
pair
Q1210
-
Q1213
,
which switches the
current
at
the
output
.
Theory of Operation - FG 5010
The
SELECTED
SQWV
signal
comes
through
line receiv
er
U1200B to
the
base
of
Q1212 and
through
R1211
to
the
emitter of
Q1211 .
The
input
impedance is
set by
R1216 ,
R1310 ,
and
R1211 ,
which
provide a 50
№
equivalent imped
ance to
U1200B
.
The
square
wave
at
the input
of
Q1212
and
Q1211
cause
Q1212
and
Q1210 to
operate in
comple
ment to one
another
.
Likewise
,
the pin 7
output
of
U1200B
,
terminated by
R1217
,
R1311
, and
R1212
,
drives
Q1215
and
Q1214
.
Thus ,
when
Q1212 and
Q1213 are
off ,
Q1210 and
Q1215 are on ,
and vice versa . Resistor R1211 sets the gain of Q1211 into
the load consisting of R1110 and R1111 . Resistor R1112
injects an additional ( constant ) current that sets the dc level
at the
base of
Q1210 . The
operating
conditions of
Q1210
are set to be approximately equal to those of Q1212 , al
though
the
voltages
are
of
opposite sign . The
voltage
swings
at the
base of
each
transistor are of
similar magni
tude and in the same direction . Thus , when Q1212 is cut off
by a more
positive
input ,
Q1210 is
turned on . The
output
impedance of Q1211 is very high , in contrast to the low
impedance presented to the base of Q1212 . This would
cause very slow transitions at the base of Q1210 . To avoid
this
effect ,
C1211
bypasses
Q1211 to
provide low -
imped
ance drive
to
Q1210 at high
frequencies . The
output current
at the
collector of Q1215 and
Q1213 is fed to the
function
selector
switch
,
depicted on
Diagram 20 .
4-31

Tektronix FG 5010 Specifications

General

Brand	Tektronix
Model	FG 5010
Category	Portable Generator
Language	English