A19 Graphics System Processor (Gsp); A20 Inverter; A16 Rear Panel - Agilent Technologies 8719ET Service Manual

8719ET/20ET/22ET
8719ES/20ES/22ES
RF Network Analyzers

A19 Graphics System Processor (GSP)

The A19 graphics system processor provides an interface between the A7 CPU and the A18
display. The CPU (A7) converts the formatted data to GSP commands and writes it to the
GSP. The GSP processes the data to obtain the necessary video signals and sends the
signals to the A18 display. It also produces VGA compatible RGB output signals which are
sent to the A22 GSP interface and then routed to the A16 rear panel. The assembly
receives one power supply voltage from the A22 GSP interface: +5VCPU, which is used for
processing and supplying power to the A20 backlight inverter and the A18 display.

A20 Inverter

The A20 backlight inverter assembly supplies the ac voltage for the backlight tube in the
A18 display assembly. This assembly takes the +5.16Vdc from the A1 mother board and
converts it to approximately 680 Vac. 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
S-parameter 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-going TTL-compatible
signal that will trigger a measurement sweep. The trigger can be set to external
through softkey functions.
Service Guide
Theory of Operation
Digital Control Theory
12- 11