Sweep Generator Yo Loop Overall Theory Of Operation - HP 8340B Manual
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Sweep Generator
—
YO Loop
Theory of Operation
SWEEP GENERATOR
-
YO
LOOP
OVERALL THEORY OF OPERATION
Main Tuning Assemblies
Four instrument assemblies provide coarse tuning for the A44 YIG Oscillator (YO), these are:
ASS
Sweep
Generator. This assembly produces
signals required
to sweep the
YO when
in
swept
instrument modes.
A54 YO Pretune/Oelay Compensation Assembly.
The A54 assembly tunes the
YO
close to the
desired output frequency. The following signals are summed on the
A54
assembly:
•
The coarse
tuning signal
(VSWP) from
the ASS
sweep generator
(during sweeps ">5
MHz
only).
•
A
microprocessor-controlled pretune voltage.
•
A
fixed
reference voltage.
The
resultant signal,
PRETUNE,
is
sent to the ASS
YO driver and the A28
SYTM
driver.
The A28
assembly
is in
the RF Section.
The
AS4 assembly delay compensation circuitry counteracts the sweep delay inherent
in
the YIG
oscillator.
This
circuit
is
controlled by the instrument microprocessor.
VCOMP
speeds the YIG
oscillator's
response
during
a
sweep. This compensates for YO eddy current-related delays.
VCOMP
is
sent to the
ASS
YO
driver.
This assembly
also
produces
a
kick pulse
(LKICK)
that eliminates
magnetic
hysteresis
in
the
YIG
oscillator. This kick pulse
is
also sent to the
ASS
YO
driver.
ASS
YO
Driver. The
ASS
YO driver sums VSWP,
VCOMP,
and LKICK and
converts them
into
a
current
signal to drive the
YIG
oscillator's main
coil.
The
ASS
assembly
is
also
in
the phase-lock
feedback
loop. Low
frequency phase/frequency error voltages are summed
into the
voltage-to-
current converter with the
VSWP, VCOMP,
and LKICK signals.
Low
frequency phase-error
correction must be input to the YO main
coil,
which can respond
to
signals
below
100 Hz. High
frequency phase-error correction
is
explained
in
the feedback loop description, below.
A47 Sense Resistor Assembly. The YO
main coil
requires
a
powerful current source. The
ASS
YO
driver can not supply the required current, so
its
output
is
amplified by the A47 sense resistor
assembly and sent
to the
YIG
oscillator's main coil.
This assembly contains the high current components
of
the
ASS
YO
driver's voltage-to-current
converter. The components are placed on the A47 assembly for proper heat dissipation. This
assembly also contains high power portions of the A28 switched YIG-tuned multiplier driver
assembly (part of
the
RF
section). This function
is
relevant to
the
RF
section.
D-2
Sweep Generator
-
YO
Loop
Theory
of
Operation
HP 8340B/41B
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