Wavetek 180 - Waveform Output; Sweep Circuits

By using current division, the magnitude of the capacitor is
effectively increased, allowing the generation of lower fre
quencies. Figure 4-3 is the simplified diagram showing
current divider operation. By reducing integration current
precisely by a factor of 10 while holding triangle wave
amplitude constant, it is possible to extend the lower fre
quency range by a factor of 10 with fixed capacitance C.
Since points A and B are at the equipotential points,
constant current output I can be divided by resistance
ratio of R and 9R. Then, Integration current of capacitor C
is reduced to 0.1 I. The lower current extends the frequency
range of the function generator by a factor of 10. The same
theory is applied to extend the frequency range by a factor
of 100.
4.3 WAVEFORM OUTPUT
The inverted output of the hysteresis switch is fed to the
TTL buffer amplifier and also the square wave shaper
(figure 4-1). The square wave shaper consists of a shaping
circuit which limits the output swing to ±1.25 volts.
The output signal from the triangle buffer amplifier is
applied to the sine converter, which uses a diode-resistor
network with linear sections to shape a sine wave.
The sine, triangle or square waveform is fed to the summing
amplifier through the waveform selector switch. The output
of summing amplifier is fed through the amplitude control
to the output amplifier. The output amplifier is an inverting
amplifier whose output is capable of driving 10V p-p into
son load from 50n source impedance.
4.4 SWEEP CIRCUITS
Sweep rate control determines the amount of integrating
current fed to the positive input of the sweep integrator
(figure 4-1). The output voltage increases linearly as the
sweep circuit capacitor is charged to form the positive slope
of the ramp. As the ramp output reaches the preset level of
+5V, the peak detector turns on while the positive feedback
circuit holds the positive output state. The large flyback
current Ip is fed to the negative input of the sweep integra
tor while overcoming minute integrating current Ir. Thus,
the ramp output decreases rapidly toward the negative
voltage, forming the negative slope of the ramp. When the
negative slope reaches zero volts, the zero detector turns
on, the peak detector is unlatched and the flyback current
source is turned off, allowing the output voltage to increase
linearly.
4-2