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10
1.4,
OPERATING PRINCIPLE
(see Fig. 1., block diagram)
The main oscillator of the function generator comprises the switched integrator and the peak detector
(comparator). The controlled current source of the d.c. contro! section generates the charging current
for the integrator. At the integrator output a linear voltage ramp is fed to the peak detector. When
reaching the reference voltage the detector reverses the charging current of the integrator resulting in
integration in the opposite direction.
Integration down
is performed until reaching the negative reference level of the peak detector, which
again reverses the current of the switched integrator. As both reference levels are symmetrical with
respect to earth, a zero symmetrical
triangular wave is generated at the output of the integrator. The
duty cycle of this wave is 1 : 1 and can be adjusted continuously between
1:9
and 9 : 1 when push-
button DUTY CYCLE is pressed.
The output current of the controlled current source depends on the positions of the frequency dia!
and the FREQUENCY
OFFSET
control. The resulting frequency of the oscillator is determined
by
this current and -in addition- by the integrating capacitor in the switched integrator. Different capacitors
are switched in by the FREQUENCY
Hz pushbuttons.
External sweep and frequency modulation can be performed via the SWEEP
INPUT socket. The voltage
to frequency relationship is linear.
The sweep range is adjustable by means of the knob START
FREQ and the dial which represents the
stop frequency. They are adjustable independantly; the start frequency may be set greater or less than
the stop frequency.
Moreover the outputs PEN LIFT and SWEEPOUTare controlled by the sweep oscillator. The PEN LIFT
socket represents the output of an electronic switch being closed during the sweep. The SWEEP OUT
socket gives the instantaneous sweep voltage corresponding to a distinct frequency
of the oscillator:
O V = start frequency, +5 V = stop frequency Fstop . The voltage to frequency relationship is linear.
The WAVE
FORM
switch allows the following wave forms to be selected: a triangular wave from the
integrator, a sine wave formed
by the sine shaper circuitry from the triangular wave,
a square wave,
negative and positive pulses from the peak detector.
The selected signal is fed to the OUTPUT socket via amplifier and attenuator. The interna! resistance
can be switched to 600 2 or to 50 £2.
By means of the DC OFFSET control a d.c. voltage can be added to the signal, activated by pulling the
PUSH
FOR ZERO switch/turn-knob. If d.c. voltage only is requested, the a.c. part of the output signal
can be switched off by pressing the DC pushbutton of the wave form selector.
A squarewave signal of the peak detector is fed to the socket TTL OUT via the TTL buffer.
The stabilized power supply provides the d.c. voltages for the circuitries.
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