Chapter 12 12-13
Theory of Operation
Digital Control Theory
A27 Inverter
The A27 backlight inverter assembly supplies the ac voltage for the backlight tube in the
A18 display assembly. This assembly takes the +5 VCPU and converts it to approximately
680 Vac steady state. At start-up the voltage can reach up to 1.5 kVac. There are two
control lines:
• Digital ON/OFF
• Analog Brightness
— 100% intensity is 0 V
— 50% intensity is 4.5 V
A16 Rear Panel
The A16 rear panel includes the following interfaces:
TEST SET I/O INTERCONNECT. This provides control signals and power to operate
duplexer test adapters.
EXT REF. This allows for a frequency reference signal input that can phase lock the
analyzer to an external frequency standard for increased frequency accuracy.
The analyzer automatically enables the external frequency reference feature when a
signal is connected to this input. When the signal is removed, the analyzer
automatically switches back to its internal frequency reference.
10 MHZ PRECISION REFERENCE. (Option 1D5) This output is connected to the
EXT REF (described above) to improve the frequency accuracy of the analyzer.
AUX INPUT. This allows for a dc or ac voltage input from an external signal source,
such as a detector or function generator, which you can then measure using the
Measure menu.(You can also use this connector as an analog output in service routines.)
EXT AM. This allows for an external analog signal input that is applied to the ALC
circuitry of the analyzer's source. This input analog signal amplitude modulates the RF
output signal.
EXT TRIG. This allows connection of an external negative TTL-compatible signal that
will trigger a measurement sweep. The trigger can be set to external through softkey
functions.
TEST SEQ. This outputs a TTL signal that can be programmed in a test sequence to be
high or low, or pulse (10 µs) high or low at the end of a sweep for a robotic part handler
interface.
LIMIT TEST. This outputs a TTL signal of the limit test results as follows:
— Pass: TTL high
— Fail: TTL low
VGA OUTPUT. This provides a video output of the analyzer display that is capable of
running a PC VGA monitor.
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