Datapulse 101 - Page 20

LLLLale—‘L’LL’L
positive,
The
sudden
drop
at
the
collector
of
Q1
also
produces
a
negative
step
through
R7
to
the
collector
of
OZ
comparable
to
the
step
that
turns
02
on
during
normal
oscillations.
This
causes
the
oscillator
to
start
promptly
at
the
leading
edge
of
the
gate,
just
as
though
it
had
been
running
before
the
gate
was
applied.
3 2, 3 Advance Trig er Amplifier
The advance trigger amplifier Q7 is designed to differentiate the
output
of
the
rate
oscillator
by
means
of
its
small
emitter
bypass
capacitor
C55. It uses the negative going edge of pulses from Q4 to produce positive
triggers
at
its
collector.
These
are
terminated
in
a
51
ohm
resistor
R62,
and applied to the advance trigger output jack.
3. 2. 4 Trigger Multivibrator
The
positive
going
output
from
Q4
is
applied
through
diode
CRSZ
to
the
trigger
multivibrator
circuit
consisting
of
CR50,
Q8
and
their
related
circuit
components.
CR50
is
a
5
milliampere
tunnel
diode
functioning
as
a
high
speed
Schmidt
Trigger
circuit.
The
current
swing
available
from
Q4
is
determined
by
the
circuit
parameters
and
is
assured
to
be
more
than
the
swing
required
to
trip
CR50
from
its
low
voltage
to
its
high
voltage
condition
and
back
again
as
the
rate
oscillator
cycles.
At each positive transition of CR50 a fast step is applied to DB,
which serves as an output pulse shaper for the trigger multivibrator. Q8
is biased by resistors R54, R55, and R57 in the on state with enough current
for high band width operation. By virtue of the small emitter bypass capacitor
C53, a sharp differentiated pulse appears at the collector of QB and is used to
trigger the delay multivibrator. Q8 also serves to prevent the reaction of the
delay multivibrator from reaching the rate generator.
3. 2.. 5 Delay Multivibrator
The delay multivibrator consists of transistors Q10 and Qll and their
related circuit components. These transistors form a complementary one-
shot multivibrator whose pulse width determines the delay interval. In order
to achieve the high ratio of delay to recovery time, the transistors are
arranged so that both are normally conducting and during the delay period,
both are turned off. At the end of the delay period, both conduct heavily,
providing a short recovery period and permitting the delay period to be almost
as long as the period of the rate oscillator.
A
negative
trigger
from
the
trigger
multivibrstor
applied
tothe
base
of
Qll
through
diode
CR51
starts
to
cut
Qll
off.
The
resulting
positive
waveform
at
the
collector
of
Qll
is
applied
to
the
base
of
010
cutting
010
off
and
causing
its
collector
to
go
negative.
This
adds
to
the
negative
signal
at
the
base
of
Qll,
completing
its
turn
off
and
causing
011
to
block
the
negative
signal
from
the
trigger
source.