Wavetek 142 - Functional Block Diagram Analysis

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