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6.
CONTROL
LOGIC
1)
General
The
control
logic
is
a
mixture
of various
logic
types
and
voltages. This
was
done
to
reduce
parts count,
cost,
and complexity.
Most
logic
is
realized
in
CMOS,
operating
from 15V
supplies.
The
logic for
NOISE
REDUCTION OPERATE/DEFEAT
and
AUTO-POLARITY ON/OFF
operates
between
ground
(LOW)
and
+15V (HIGH)
to
allow the
most
simple
interfacing
between
the
logic
and
the circuits being controlled.
All
other
CMOS
operates
between
-15
(LOW)
and ground (HIGH).
Discrete diode
logic
is
mixed
with
the
CMOS
wherever
use of such discrete
logic
would
simplify the
circuitry.
2)
Comb
Bandwidth
[Logic operates
between -15V (LOW)
and ground (HIGH)].
IC27a, IC27b
are
crosscoupled
to
form
an
RS
flip-flop circuit
which "remembers"
its
state
until
switched
to a
new
one by
a
momentary
pulse or
continuous
signal
(it
doesn't
care which).
Its
inputs are
provided by front-panel switches
S6, S7,
as well
as
by
optoisolators IC57,
IC62 which
isolate
the
User Control
Interface
from
the
logic.
When
Q401
turns
on
(collector at -15V),
Q105
turns
off.
This
permits
the output of
phase
shifter
IC8b
to
feed
signal
through
R195
into
buffer amplifier IC4b.
All
other
phase
shifters
are bypassed,
and
a
WIDE comb
bandwidth
is
generated.
When
Q401
turns off (collector
floating),
Q105
turns
ON
through R190.
This
connects
the output of
phase
shifter
IC5a
to
the input of
IC4b and
swamps
out
any
significant signal
leakage through R195, switching
all
phase
shifters into
the
circuit
and
providing
a
NARROW
comb
bandwidth.
When
Q402
is
off,
current flows through
DS11
(NARROW
LED),
CR401, CR402,
and
R413.
R413
provides current
limiting.
When Q402
is
on,
its
voltage drop
is
lower
than
that
of
CR401,
CR402
in
series.
Therefore, current
is
shunted
away from
DS11
and
flows
instead
in
DS10 (WIDE
LED).
(This "tree" principle of logic
decoding
for
the
lamps
is
used,
in
a
more complex
way,
for
the yellow
STANDBY
lamps
as well.)
3)
NOISE
REDUCTION OPERATE/DEFEAT
[Logic operates
between
ground
(LOW)
and +15 (HIGH)].
IC26a,
IC26b form
an
RS
flip-flop.
Q404
turns
on
to disable
the operation
of
IC12
through
CR102, CR103. However,
signal
still
flows
through
IC12 even
when
the
Noise Reduction function
is
OFF.
6-7
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