Viper 60s Theory Of Operation And Maintenance Manual page 138

THEORY OF OPERA TION
6.2.4 Tape Hole Sensor
This circuit consists largely of a two hole sensor circuit and a comparator circuits. These
circuits eliminate the need for various potentiometer adjustments due to changes
in
tape
transmissivity and sensor characteristics.
6.2.5 Phase Lock Loop
This circuit consists of a loop filter and a voltage controlled oscillator. The loop filter consists
of several operational amplifier stages followed by the veo and corresponding circuits.
Total phase-Iock-Ioop operation makes use of these circuits and phase and frequency com-
parison circuits located in the VLSI.
The phase-lock-loop operation makes use of two signals: -AQA and -TRKA. These signals
represent the two modes of operation: frequency lock acquire and frequency phase-Iock-
tracking.
When operation begins, the system is in the frequency lock acquire mode. This mode of
operation makes sure that signals are within range of an actual frequency and do not
represent an unwanted harmonic. As soon as a fundamental frequency signal is obtained,
operation moves to the frequency phase-lock-tracking mode. Two potentiometers are pro-
vided for phase lock offset adjustment and for veo Range Adjustment.
6.2.6 Reset Circuits
A system reset is generated if the power supply voltage drops below a predetermined level.
This reset function is accomplished by two monolithic integrated circuits. These reset control-
lers generate the SRST and -SRST Signals. The SeSI bus reset also generates a -SRST signal
output.
6-7