Philips PM 5131 Mode D'emploi Et D'entretien page 8

8
1.4.
OPERATING PRINCIPLE (see Fig.
1., block
diagram)
The oscillator of the function generator comprises the switched integrator and the Reak detector (comparator).
The controlled current source of the d.c. control 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.
The output current of the controlled current source depends on the positions of the frequency dial 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. Internal frequency control of the main oscillator for single sweep is effected
by the sweeQ control, started by the SGLE SWEEP pushbutton. The sweep range can be adjusted by the
SWP STOP/START control. The SWP PERIOD turn-knob adjusts the sweep time.
The instantaneous (sweep) voltage corresponding to a distinct frequency of the oscillator is available at the
SWP VOLTAGE IN/OUT socket. Via this socket external sweep or frequency modulation can be performed.
The voltage to frequency relationship is logarithmical, corresponding to the transfer characteristic of the
controlled current source.
The WAVE FORM switch allows the following wave forms to be selected: a triangular wave from the integrator,
a squarewave fro.m the peak detector or a sinewave formed by the sine shaper circuitry. The signal is fed to the
OUTPUT socket via AMPLITUDE potentiometer,
amQiifi1~
and attenuator.
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 via the TTL buffer to the TTL OUT socket.
The stabilized power supply provides the d.c. voltages for the circuitries.