Wavetek 3000 Instruction Manual page 33

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MODOLATINfr
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positive source is
referenced to the
negative source
so that the instantan-
eous currents in both sources are equal .
3 .10 .2 Oscillator
The change in output current is directly
proportional to the change in input vol-
tage to the circuit .
The input voltage
may vary
between -5 and +5 volts .
The
circuit is
designed for a very
linear
current-out vs . voltage-in curve .
The square wave output is produced
by
the combination
of an integrator and a
hysteresis switch .
The integrator con-
verts a square wave to a triangle wave .
The triangle wave causes the hysteresis
switch to produce the square wave which
is fed back to the integrator .
The integrator is
made up of a current
switch and a
capacitor . The square
wave applied to the current switch causes
a square
current signal to be
applied
to the capacitor .
Positive constant current produces
an
increasing voltage ramp on the capacitor
and negative
constant current produces
Figure 3-15 .
M29-1 - FM Reference
THEORY OF OPERATION
l. S- 2 . S Mf/z
a decreasing voltage ramp .
For a square
wave input,
therefore, the output is a
triangle wave .
Changing the magnitude of the "currents",
by changing the
input voltage to the
module, changes the rate at
which the
capacitor charges and discharges to the
hysteresis points thus the frequency of
oscillation changes .
3 .11 M30 - CRYSTAL REFERENCE
This module supplies reference frequen-
cies at 1 kHz, 1 MHz, 2 MHz, 40 MHz
and
its harmonics, 1200 MHz (from 120 comb)
and 1440 MHz to the phase locked loops
in the instrument . These signals are
produced by a 40 MHz crystal oscillator
and a series of dividers and multipliers .
See Figure 3-16 .
3 .11 .1 40 MHz Oscillator
This crystal oscillator is the heart of
the accuracy of the frequency determining
circuits in the instrument .
It is tem-
perature compensated
for frequency
stability .
A leveler circuit causes the
oscillator output level to be the same
in all M30 modules .
3-15