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
voltage, (4) the VCG analog voltage input and (5) the
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 (P RSG).
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). I n 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
output connector.
All circuits, except for the hysteresis switch, output
amplifier, and PRSG, operate from
volt supplies.
The hysteresis switch and power amplifier require
volts and
volts, respectively. Operation of the
PRSG requires a +5 V supply.
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