Tektronix FG 5010 User Manual

Theory of
Operation - FG
5010
LOOP 1 SECTION
INTRODUCTION
The Loop 1
Section
consists
of the
following major
circuits , which are depicted on Diagrams 10 through 14 :
Reference Section , Symmetry Circuits , Main Loop , Shrink
Control , and Clamp circuits . Although the Digital Control
Circuits exist on several of the diagrams , they are discussed
as
a group in detail
at the
beginning of this
discussion , and
only referred to in context thereafter .
LOOP 1 BLOCK DIAGRAM DESCRIPTION
Refer to the block diagram for the Loop 1 section , in the
foldout pages of this manual . The Loop 1 Circuits form the
main analog signal generating source in the FG 5010. It is in
Loop 1 where the triangle and squarewave signals are
generated . Sinewaves are formed in the Sine Shaper
section by alteration of the triangle waves from Loop 1 .
Beginning at
the left side
of the block
diagram
, the
FM / VCF input signal is fed to the Frequency Reference
Selector , which consists of a buffer , summing amplifier , and
several transmission gates . Under control of the CPU , the
Frequency Reference Selector applies some combination of
the VCF voltage , the Frequency DAC , and the LOCK Freq
control voltage signal to the summing amplifier , to produce a
frequency control voltage that is proportional to the dc input
voltages and
the
applied digital
control
information . Also
under
digital control
, the circuit
diverts the
FM control
voltage to
the
Frequency DAC
circuit .
The +10 V
Reference
Source is
an
operational amplifier
that produces the reference voltage that is applied to the
DAC Reference Amplifier , the Shrink Control Current
Sources , and
the DAC
.
The DAC Reference Amplifier sums the +10 V reference
voltage with the incoming FM control signal , if applied , and
sends the combined output to the Frequency DAC circuit for
application as the analog reference voltage .
The Frequency DAC produces a dc voltage that is
proportional
to the
voltage
applied from
the DAC
Reference
Amplifier and the digital data that is applied to the DAC . This
output from the DAC is applied to the Frequency Reference
Selector
for
summing
with
other inputs .
4-6
The Up Symmetry DAC and Down Symmetry DAC
furnish the control voltages that determine the symmetry of
the two slopes of the triangle - wave signal generated by the
loop . The Frequency Control Voltage from the Frequency
Reference Selector is applied to both of the symmetry
circuits , modified by the digital control of the circuits by the
CPU , then fed out to the Up Ramp Current Source and
Down Ramp Current Source as Vup and VDN , respectively .
The Up Ramp Current Source and Down Ramp Current
Source circuits are operational amplifiers that convert the
incoming voltage to dc current , applied as the charging
current sources to the Transistor Bridge circuit .
The current supplied to the Transistor Bridge is switched
by
the bridge to
provide the charge
and
discharge current
for
the Loop
Capacitors .
Control
signals for the
Transistor
Bridge are
supplied
by the
Bridge
Buffer ,
in the form
of
differential
square
waves .
The Bridge Buffer receives the squarewave signal from
the Level Detector , and applies the squarewave signal to
the Transistor Bridge , which causes the currents to the
Loop Capacitors to be switched at the proper time . The
Buffer also supplies a square wave to the High Frequency
Squarewave
Buffer
circuit .
From the output of the Transistor Bridge , the triangle
wave
is applied
to the
Triangle Buffer . This
circuit
supplies
the
triangle
wave to the
Triangle
Selector , which
selects
between the low - frequency triangle signal or the high
frequency triangle - wave signal . The output of the Triangle
Buffer is also fed to the Level Detector , a Schmitt trigger
circuit . Level detection is the process by which the triangle
wave
signal passes
voltage trip
points
,
first
switching the
detector
outputs
sharply in one
direction , then the
next . This
produces the
square - wave
that is
supplied to the Bridge
Buffer . Two current inputs of opposite polarity are also fed
to the level Detector to modify the switching point of the
Level Detector . This input compensates for switching delays
in the loop that might otherwise cause frequency distortion
of the
triangle - wave
signal .
The Phase Clamp Diode , which is also connected to the
Loop Capacitors , steers the charging current away from the
capacitor to prevent the loop from free - running when gated ,
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Tektronix FG 5010 Specifications

General

Brand	Tektronix
Model	FG 5010
Category	Portable Generator
Language	English