Wavetek 142 - Page 19

voltage
followers
whose
output is
fed back
to
Q12 and
Q13
through R46,
R47,
R54,
and R55
forming
the flip-
flop
configuration.
Q9
is
connected
as a
7-volt
zener
reference
for IC1
and the
flip-flop.
In
the
state
where Q13
is
conducting
and
Q12 is
cut
off,
the
voltage
at
the
emitter
of
Q16
is
high
(-t2.5
V)
and
the
voltage
at the
emitter
of
Q11 is
low
(—2.5 V).
Once
tunnel diode
CR13
is
turned
on by
IC1,
the
V^e
of Q15
will
increase
until Q15
turns
on and in
turn
Q13 is
turned
off. This
causes
the
emitter
voltage
of
Q16 to
drop
to
—2.5
V
which,
through
feedback
resistors R47
and
R46,
keeps
Q12
in tne
on
state.
Thus the
emitter
voltage of
Q11 will rise
to
-i-2.5
volts.
Although
the
tunnel diode
CR13
is
turned
on only a
very
short
time
during
the
peak
of the
triangle
waveform,
Q13
will remain
in
the
off state
because
of
the feedback
through
R46,
R47,
R54, and
R55.
The
output
of
Q11 is used
to
drive
the diode
gate.
3.2.4
Diode
Gate
As
shown in
Figure
3-4,
the Diode
Gate
consists
of four
diodes, CR7
through GRID.
Assume
that the
voltage at
point C
is
-1-2.5
V.
Diodes CR7
and CR9 are
then
forward
biased, and CR8
and CR10
are reverse
biased.
The
negative
current source
(I—)
will draw
current
from
the Hysteresis
Switch
through CR9,
but
the positive
current
source
(l-t)
will
charge up
the
timing capacitor "C"
through
CR7. The
Figure
3-4
-
Simplified Diode Gate
Diagram
result is a
linear rise
of voltage
across
the timing
capacitor.
When this
voitage
reaches -H.25
volts,
the output
of the
Hysteresis
Switch
will change to
—2.5 volts. In
this state,
CR8 and CR10
are forward
biased
and CR7
and CR9 are
reverse
biased. The
positive
current
will be
diverted to
the Hysteresis
Switch
through GRID
and the
negative
current
source
will
draw current
from the
timing
capacitor
through GR8.
This action
causes a
linear discharge of
the
timing
capacitor.
The
process is
repeated, thus a
triangle
waveform
is
generated.
3.2.5 Sine
Gonverter and
Amplifier
The
Sine
Gonverter is a
sealed subassembly
containing
matched diodes and
precise
current-biasing resistive net-
works. When a
precise
triangle wave is fed into
the shaping
network,
through voltage
divider R149 and RMS, the
triangle wave
is shaped into a sine wave. Potentiometers
R159
and R168 adjust the
voltage supplied to
the
sine
converter to obtain
minimum sine
distortion. The ampli-
tude
of the sine converter output
is
approximately 150 mV
p-p.
This
voltage is amplified to
approximately
2.5
V
p-p
by
the Sine Amplifier.
The Sine
Amplifier
consists of
transistors
Q30
through
Q35
connected as a
differential
feedback
amplifier. The
gain of
the
amplifier is
controlled by
R165, R164,
and R158.
R145
and
R146
compensate the
source
current into Q30
to
minimize the
distortion of
the sine
converter output.
3.2.6 Square
Amplifier
The
inverted
output from
Hysteresis
Switch Q16
(±2.5
volt square wave) is
fed to
the Square
Wave
Shaper com-
prised of GR14
through GR19.
For
a
square
wave output,
GR14 and GR19
are
reverse
biased. In one
state,
if the
cathode
voltage of GR15
is
+2.5
volts, GR15 and
GR17
will be
reverse biased
and
GR16 and GR18
will be
forward
biased.
The
output at the
cathode
of GR18
is limited to
+1.25
volts by
the
current
through R63
and R64
into
R69. When
the input voltage
is
switched to
—2.5
volts,
GR15 and
GR17
will be
forward biased and
GR16
and
GR18
will be
reverse
biased,
limiting the
output at the
cathode
of GR18 to
—1.25
volts by the
current
through
R66 and
R67 into R69.
When the
positive
pulse output
is
selected
by
the
WAVE-
FORM SELEGTOR
switch, the
cathode of GR14
is
con-
nected to
ground
through R61. In
this
configuration,
the
output at
the
anode of GR18
will be limited
to a
voltage
swing of
—1.25
and
zero. Because
the output
amplifier
is an inverting
amplifier,
the signal at
the
50fi
OUT con-
nector will be a
positive pulse.
In a
similar manner,
when
the
anode
of
GR19
is connected
to
ground
through R61,
the output swing at
the
cathode
of
GR18
will be limited
to
zero and
+1.25
volts, resulting
in
a
negative
pulse at
the
50J2
OUT
connector.
G26
is a
high frequency
filter to
filter
the
high
frequency
noise on
the
square
wave,
resulting in a
cleaner
signal.
At this
point,
the
output
signal is
buffered by
a
double
emitter
follower
stage
consisting of 017
and
018,
and
the
output at
the
common
emitters is
applied to
the
output
amplifier
through
the
contacts
of the
WAVEFORM
SE-
LEGTOR switch.
3-5
11/70