The servo controller circuit consists of several
op-amps and Transistor-Transistor Logic
(TTL) components. Its purpose is to
convert a DC voltage into a rectangular
pulse train whose duty cycle is determined by the DC level.
The servo responds to variations in the duty cycle of a 50 Hz
rectangular pulse train. The controller circuit is designed to
produce a 50 Hz rectangular pulse train with a duty cycle determined
by the DC voltage level at its input.
The path of the signal through the circuit is shown in the block
diagram of Figure 
. A summary of each component is provided
in the following section.