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amplifiers
must
have good high frequency
characteristics since
square
waves
up
to
1
MHz
must
be controlled.
As
a result, the
basic circuitry
is
also
cap-
able
of
a
wide band frequency modulation.
The
sine
wave
is
produced by
shaping
the triangle
wave.
The
triangle
wave
is
fed
into
a
shaping
network
composed
of
resistors and diodes with transistor
emitter follower biasing
circuitry.
As
the
triangle
wave
passes through
zero,
loading
of
the triangle
wave
is
minimal
and
thus slope
is
maximum.
As
the
triangle
wave
voltage
increases successively, diodes with current
limiting
resistors
conduct causing
the
slope
of
the
output
to
be
less.
The
resultant
waveform
resembles
a sine
wave
but
is
pointed
at the top.
The
diodes are
biased
by
transistor emitter followers
whose
base emitter
junctions
are op-
posite
in
polarity
from
the
diodes.
This provides
a
first
order compensation
for drifts
due
to
temperature
variations.
The
increase
in
diode
current
at the
peak
of
the triangle
wave
causes
a pointed voltage pattern on
the collectors
of
the
emitter followers.
This
pointed
waveform
is
combined
out
of
phase
with
the
somewhat
pointed
sine
wave.
The
resultant
waveform
is
an almost pure
sine
wave.
The
circuitry
is
completely
symmetrical
about
ground
using
PNP
transistors
on
one
side
and
NPN
transistors
on
the other.
The
sine
wave
pro-
duced by shaping
is
considerably
less
in
amplitude than
the
triangle
wave
input
and
is
thus
amplified
to
be equal
to
the triangle
wave.
The
triangle
wave,
sine
wave
and square
wave
outputs
are
resistively divided
down
to
provide
fixed
1
volt
peak
to
peak
outputs
into
a
5
On.
load.
These
same
waveforms
are
selected
by
the
amplitude multiplier and
three
dials.
The
three
waveforms
(triangle,
sine
and square) are adjusted
to
appropriate
relative
amplitudes by
resistive
networks.
One
of
these
waveforms
is
selected
by
the
function switch
which
connects
it
to
the
amplitude
digital to
analog con-
verter through
a buffer
amplifier.
The
amplitude
D
to
A
converter feeds
signal
current
into the
output amplifier
summing mode
to
an
extent
determined by
the digital
program.
The
signal
voltage out
of the
output amplifier
is
then proportional
to
the digital
program.
The
output amplifier output
is
connected
to
the
output
BNC
connector through
an
attenuator
which
divides
the
amplifier output by
1,
10
or 100
depending on
the
amplitude range
program.
The
output attenuator
is
designed with
a
50n
output
impedance
so
that
when
it
is
operated
into
a
50^1.
load,
the output will
be
the
value indicated by
the
pro-
gram.
When
operated
into
an open
circuit, the
output
will
be
approximately
twice
the
value indicated
by
the
program.
4-3
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