Wavetek 132 - Page 15

tion.
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 magnitude
of the
capacitor
across the
integrator
and amplitude
of the
current
into the integrator
deter-
mine the
frequency of
oscillation.
Capacitance across
the
integrator
is changed
by
rotating
the frequency
Hz
selector.
Amplitude of
the current into the
integrator
is determined
by
four
parameters
which are
summed
in the
VCG circuit:
(1)
hysteresis switch
output,
(2)
the
frequency
dial voltage,
(3)
the
frequency
vernier
vouage,
(hj tne
vi^u analog
voltage input
ana tne
analog
noise when
in the
FM
mode.
The
sine wave
is
produced
by feeding the triangle
wave
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
maximum.
As
the triangle
voltage in-
creases,
diodes with
current
limiting resistors
conduct
and
successively
cause
the
slope of
the
output to be
reduced.
Since the
diode break
points are
mathematically com-
puted and
fitted to the
true
sine shape, the
resultant
waveform
resembles
a
pure
sine wave.
Using
a com-
plementary
pair of
diodes
on
each break
point,
the
circuitry
is completely
symmetrical
about
ground. 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.
Either square, triangle, or
sine waveforms
can be se-
lected
as a signal source. The noise source
is derived
from
a
digital filter.
A
clock oscillator of
160
Hz
to
1.6
MHz range
functions
as a
trigger
source for
the
digital
pseudo-random sequence generator
(PRSG).
Output
of the
PRSG is a
random binary
signal
that
can
function
as digital noise. The number of
bits
in
each
sequence
can be selected
by
the
SEQUENCE
LENGTH controls.
Parallel data is fed from
the
PRSG
to the
digital-to-analog converter where
the
informa-
tion is summed
and
filtered
to provide
a random
analog noise signal.
The selected
sine, triangle, square, analog
noise, or
digital noise
signal is routed to the
mode control
circuitry
where
one
of the following
modes of opera-
tion
is
selected:
Function (FUNC); frequency
modula-
tion
(FM); signal-to-noise
(S/N); or noise-to-signal
(N/S). In the signal-to-noise
and noise-to-signal
modes,
one signal
is
fed
to the
S/N
attenuator
and then mixed
with
the other signal
in
the
S/N summing amplifier
in
a
known
dB
ratio
selected
by
the
S/N attenuator.
Out-
put
of
the
mode switching circuit is
coupled
to
the
output amplifier.
From the output amplifier
the signal
is
fed
to the
precision
output attenuator
and finally to
a 500 output
connector.
Ail
circuits, except for the
hysteresis switch,
output
amplifier,
and PRSG,
operate
from
±15 volt
supplies.
The
hysteresis switch and power
amplifier
require
±6
volts
and
±22
volts,
respectively.
Operation of
the
PRSG requires
a
+5
V supply.
12