Circuit Description - BWD MINI-LAB 603B Manual

6
.
CIRCUIT DESCRIPTION
(continued)
6.2 Triangle
and Square
Wave
Generators
(Drg.
No.
1358) (Cont'd)
\AA
JTT
The
variable voltage
produced by
the
frequency
vernier
is
amplified
and
inverted to
produce two
equal
and
opposite voltages which
control the
two
current sources.
The
current switch passes either
i]
or i£
to
Ct
the
timing capacitor,
producing
a
linear
voltage ramp which
is
4ve
going
when
i] is
applied and -ve
when
12
applied.
The
signal across
Ct
is
passed
through the
buffer amplifier,
which
has
a very
high input
impedance,
to the
comparator.
Hysteresis of the
comparator enables
the input
waveform
to
operate
between +0.6V and -0.6V
with switching occurring at
+
and -0.6V.
Assuming
the
comparator
is
switched
in
such a
way
as
to
allow the current
switch
to pass
i],
the
voltage
across
Ct
rises positively, as
does the output
of the buffer amplifier.
As
the
output
of
the buffer amplifier,
and hence
the comparator
input,
reaches +0.6V, the output of the comparator
will
change and
via the current
switch
will
remove
i],
and
substitute
i
2
in
its
place.
The voltage
across
Ct
will
now
increase
in
a
negative direction
until
the
comparator
input
becomes -0.6V. The comparator output
will
change
state
and
return the
current switch
to
the
initial
state, passing
i]
,
to
Ct.
603B 6
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1