General Description - Wavetek 130 Instruction Manual

SECTION
3
CIRCUIT
DESCRIPTION
GENERAL
DESCRIPTION
Refer to the block diagram of the
Model 130
Function
Generator, Figure 3-1.
A
square
wave
is
applied to the
input
of an integrator.
The output
of the integrator, a triangle
wave
is
fed
into a hysteresis switch.
The
hysteresis/output switch
functions
like
a
Schmitt
trigger
with the
limit points
set at
the
waveform
extremes,
firing
when
the triangle
wave
reaches -H.25
volts
and —1.25
volts.
The
firing
sets
the hysteresis
and
the output switches
which
reverse
the square wave fed
into the integrator, causing
the
triangle
wave
to reverse direction.
The
result
is
simultaneous generation of
a
square
wave
and
triangle
wave
of the
same
frequency with the
positive half
cycle of the square
wave
coincident
with the
negative
slope of the
triangle
wave.
The
frequency
of oscillation
is
determined
by
the
magnitude
of capacitor
C
selected
with the
FREQ HZ
switch
and by
the amplitude of the square
wave
fed
into
the
integrating resistor R.
The ±5
volt
square
wave
is
fed to the frequency
dial
potentiometer. Setting the
potentiometer
for
maximum
voltage,
and thus maxi-
mum
integrating current, produces an output
at
maxi-
mum
frequency. Frequency
is
directly
proportional to
the square
wave
amplitude
appearing
on the
arm
of the
frequency
dial
potentiometer.
The
sine
wave
is
produced by
shaping the
triangle
wave.
The
triangle
wave
is
fed into a shaping
network
composed
of
resistors
and
diodes.
As
the
triangle
wave
voltage
passes
through zero, loading of the
triangle
wave
is
minimal and thus
the slope
is
maxi-
mum.
As
the triangle
wave
voltage
increases;
diodes
with current
limiting resistors
conduct,
successively,
causing
the slope of the output
to
be
less.
Since the diode break
points are
mathematically com-
puted
and
fitted to
the true
sine shape,
the resultant
waveform
is
an almost pure sine
wave. The
circuitry
is
completely symmetrical about ground,
using a
complimentary
pair
of diodes on
each break point.
The
sine
wave
produced
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
output of the
integrator,
the
sine
wave
output, and
the square
wave
coupled through
a
divider are fed to the function
selector switch.
The
switch
is
coupled
to the attenuator
which
in
turn
drives the output
power
amplifier.
All
instrument
circuits,
except the switch
set
and
the
power
amplifier
output
stage,
operate with regulated
±15
volt supplies.
The
switch
set requires regulated
±6
volts.
The
power
amplifier output stage requires
unregulated
±22
volts.
5