HP 8340b User Manual

A42
PLL2
Divider
Refer
to
Figure
C-1.
The
next
assembly
is
(functionally)
the
A42 PLL2
divider.
This
assembly
converts
the
output
of the
VCO,
which
is
sweeping
during
many
instrument
modes,
to
a
fixed
500
KHz
output.
To accomplish this,
a
microprocessor-controlled
fractional divider
anticipates
the
instantaneous fre¬
quency
and divides
it
by
a
programmed amount.
The
output
signal
contains
any
phase/frequency
error present
in
the original
VCO
output,
and
is
sent
to
the
A41
PLL2
phase
detector.
This
assembly also
divides
a
reference
signal
from
the
reference
loop
for
use
by
the
A41
PLL2
phase
detector.
A41
PLL2
Phase
Detector
In
CW/Manual
operation,
this
circuit
passes
phase-error
Information
directly
to
the
A43
PLL2
discriml-
nator.
During
swept
modes
the
phase-lock
loop
path
is
closed
during
the
pre-sweep
interval,
and
a
sample
and
hold
circuit
stores
the
phase/frequency
error
voltage.
The
start
of
sweep
Is
established
with
phase-lock
precision.
The
phase-lock
loop
path
opens
and
a
precision
voltage
ramp sweeps
the
VCO
via
the
A43
PLL2
discriminator.
A43
PLL3
Discriminator
This
assembly
sums
two
VCO
tuning inputs
and
two
feedback
paths
into
a
voltage-to-current con¬
verter.
The
output
is
used
to
tune
the
A40
PLL2
VCO.
The
inputs to
the
summing
circuit
are
listed
below:
Tuning
Inputs:
•
20-30
precision
sweep
signal
from
the
ASS
sweep generator
•
Microprocessor-controlled
pretune
signal
from
a
digital-to-analog
converter.
Feedback Inputs:
•
Analog
feedback
from
the
A40
PLL2
VCO.
•
Phase/frequency
error
voltage
from
the
A41
phase detector
The
discriminator
is
a
very accurate voltage-to-current converter
that
provides
the
PLL2
loop with
extremely
linear
performance.
While
the
phase-lock
loop
is
locked,
the
20-30
sweep
input
is
zero volts,
and
the
phase
detector tunes
the
VCO
by
changing
the
frequency-to-current
ratio
of the
discriminator,
After
phase-lock
is
estab¬
lished,
the
phase-lock
error
voltage stored
in
the
A41
assembly's sample
and
hold
removes
any
warmup or
drift
effects.
The
20-30
input
is
then
swept,
sweeping
the
VCO
frequency.
The
analog
feedback
loop
provides
negative
feedback
to
the
discriminator, exactly
canceling
the
voltage
intro¬
duced
at
the
input to
the
discriminator
summing amplifier.
HP
8340B/41B
20-30
Loops
Overall
Theory
of
Operation C-5

HP 8340b Specifications

General

Brand	HP
Model	8340b
Category	Inverter
Language	English