Functional Block Diagram Analysis - Wavetek 142 Instruction Manual

3.2
FUNCTIONAL BLOCK
DIAGRAM
ANALYSIS
As
each
functional circuit
is
described, refer to
the
appropriate block
diagram
and,
if
necessary,
the appro-
priate
portions of the schematic diagrams
at
the
rear
of
this
manual.
3.2.1
VCG
Amplifier
and Current Sources
As shown
in
Figure
3-3,
IC2
is
connected
as a
Summing
Amplifier
to
sum
the
VCG
input current through
R89,
the current
from the
FREQ
DIAL
R82, and
the current
from the
VERNIER
control
R90. IC2
is
an
inverting
+15
Figure 3-3
-
VCG
Amplifier
and Current Sources
amplifier
whose output voltage will
change
from 0
to
—5
volts
under normal
operating conditions. Transistor
Q21
limits
the
output swing
to
0 and
—7
volts.
The
output
of
IC2
is
used to control
both the positive
and negative
current sources,
ICS through
ICG.
The
negative input of
ICS
is
held
at
0
volts
by
its
feed-
back.
The
current
through
R101 would
be directly pro-
portional to the
output
voltage of
IC2
if all
the source
currents of
ICS and IC5 are neglected,
and
the current
through
R116 would
be
equal to the current
through
3-3