Wavetek 193 Instruction Manual page 28

current. The output is fed via the function switch to
the preamplifier.
The trigger circuit allows precise single or multiple
(gated) cycles at the output in response to external
trigger signals or manual trigger operation. The trig-
ger circuit operates by holding the timing capacitor at
o
volts, via the loop stop signal, on the positive going
triangle ramp, until a trigger signal occurs. In the TRIG
mode a single cycle is produced for each trigger
signal above the variable trigger level threshold. In the
GATED mode continuous cycles are generated for the
time period at which the external signal is above the
trigger level threshold plus the time for completion of
the last partial cycle. The RUN signal causes the
SYNC output to stay in the low state when the
generator is quiescent. The TRG RSTsignal resets the
trigger circuit and generator to the quiescent state on
every generator cycle to arm it for the next trigger
input. The trigger baseline compensation, LOOP
STOP,circuit holds the generator output at zero volts,
LOOP STOP,(within specified limits) during the quies-
cent intervals at any position (value) of the frequency
dial, FREQ MULT, VCG IN, or VERNIER.
The sync circuit accepts the square wave signal from
the hysteresis switch or zero crossing detector and
converts it to a true 50n TTL level output. In square
wave function (SYNC SELECTenabled) the sync is in
phase with the output, but in triangle or sine functions
(SYNC SELECTdisabled), the zero crossing detector
causes the sync output to be in phase withthe zero
crossing of the output waveform.
When square is selected by the function switch, the
square shaper accepts the signal from the hysteresis
switch and converts it to a clean, fast square wave
current which drives the preamplifier. In sine, triangle
or DC functions, the square shaper input and output
are disabled so as not to interfere with the selected
waveform.
The preamplifier is fed from both the function switch
and the square shaper. In all functions except AM, the
preamplifier voltage output drives the output amplifier
via the amplitude control. But when the AM function is
selected, the voltage output (carrier signal) drives the
amplitude modulator on the Sweep/Mod board.
The output amplifier receives input signals from a sec-
tion of the function switch via the amplitude control
and drives the output attenuator. DC offset is achieved
by offsetting the output amplifier.
The output attenuator, fed directly from the output
amplifier, provides up to 70 dB of attenuation to the
selected waveform or DC offset. This signal is con-
nected directly to the FUNC OUT BNC.
4-2
On the X1M and X1OM ranges the dc loop delay com-
pensation circuit compensates for delays in the
generator loop. This circuit causes the hysteresis
switch trip polnts to switch earlier in the cycle, and
prevents the timing capacitors from charging beyond
± 1.0V. The switch points are adjusted in proportion
to the charging current, thus ensuring a constant
amplitude as frequency is varied.
The capacitance multiplier is an active circuit which
simulates capacitors up to 10,000 times larger than
the timing capacitor, thus allowing very long charging
times using physically small capacitors. This circuit is
used in the four lowest frequency ranges.
The sine converter accepts a ± 1.0 volt triangle signal
from the triangle buffer and converts it to a sine wave
pensation. The GCV amplifier provides a dc voltage
proportional to the main generator frequency.
The current switch, controlled by the hysteresis out-
put, causes either the positive current source or the
negative current source to charge the timing
capacitor selected by the frequency multiplier. When
the positive current source is switched in, the charge
on the timing capacitor will rise linearly producing the
positive-going triangle slope. Likewise the negative
current source produces the negative going triangle
slope.
The triangle buffer amplifier is a unity gain amplifier
whose output is fed to the hysteresis switch, sine con-
verter and function switch. The hysteresis switch
operates as a "window" comparator with limit points
set to the triangle peaks. When the positive going
ramp reaches
+
1.0V,the hysteresis switch toggles to
a low state causing the current switch to connect the
negative current source. This causes the timing
capacitor voltage to linearly ramp to -1.0V. As the
timing capacitor voltage reaches -1.0V, the
hysteresis switch toggles to a high state, switching in
the positive current source. The generator loop con-
tinues to oscillate producing simultaneous triangle
and square waves, at a frequency determined by the
frequency multiplier and the magnitude of the timing
current controlled by the sum of the dial setting, the
VCG input, and the vernier.
Depressing the SYM button produces an unsym-
metrical waveform and a division of the frequency by
a factor of 10. The VERNIER/SYMcontrol creates an
imbalance in the current sources and therefore an im-
balance in the waveform symmetry up to a ratio of
19:1. The result is variable duty cycle pulse, variable
askewed sine wave and variable "sawtooth" triangle
waves.