Agilent Technologies 8590 Series Service Manual page 374

Assembly Descriptions and Block Diagrams
IF Section
A12 Amplitude Control
The A12 amplitude control assembly provides gain or attenuation in
eight stages: three step-gain amplifiers and five step attenuators. All
stages, except the 10 dB step gain, provide full gain or attenuation
when turned on and unity gain when turned off. The 10 dB step gain
has a gain of 15 dB when on and a gain of 5 dB when off.
When the reference level is changed, the A7 analog interface assembly
interprets the A16 processor/video assembly commands and produces
the appropriate combination of gain and attenuation control voltages in
1 dB increments. Reference-level resolution of less than 1 dB is
produced by mathematically offsetting the digitized video signal on the
A16 processor/video assembly.
A12 step-gain errors are corrected by correction factors produced by the
self-calibration routine. Each correction factor is an offset
CAL AMPTD
of the digitized video signal and is stored in nonvolatile memory on the
A16 assembly.
A12 step-attenuator errors are corrected by correction constants that
are characterized values initially installed at the factory. The corrected
calibration attenuators provide the amplitude reference used by
self-calibration routine.
AMPTD
A13 Bandwidth Filter
The A13 bandwidth filter assembly is identical to the A11 assembly.
Refer to the A11 assembly description in this section.
After leaving the A13 assembly, the 21.4 MHz IF signal branches on the
A15 motherboard:
• One branch passes directly to the A14 log amplifier assembly.
• A buffer amplifier on the A15 motherboard attenuates the IF signal
by 20 dB and distributes it to the card-cage assemblies (AUX_IF),
the rear panel AUX IF OUTPUT connector (AUX_IF_BP), and the
A25 counterlock assembly (COUNT_IF). The COUNT_IF signal is
used by the A25 assembly to count the actual IF frequency when
is selected.
MKR CNT ON
• Another buffer amplifier on the A15 assembly sends the IF signal
(AUX_IF) to assemblies installed in the card cage.
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CAL
Chapter 9