Tektronix RTX100B, Service Manual

Page: 43 / 178

Theory of Operation
RTX100B ISDB-T RF Signal Generator Service Manual
2-5
This block steps down an RF output level to the antenna input level of a receiver
and matches the impedance with 75 Ω .
Front-Panel Processor Board
The Front-Panel Processor board consists of the following circuitries and
connectors:
The state of the front-panel keys are read by the one chip processor on the board
and any setting changes are reported to the SBC through the COM2. The
processor also controls the LED on/off state of the front-panel LEDs.
The LVDS data from the SBC is routed through the board to the LCD.
When the Window OS puts the instrument into power saver mode, the LVDS
data from the SBC stops and the LCD backlight needs to be turned off or a
rainbow display will occur. When the LVDS data stops, the common mode
voltage of the data lines changes from the 1.25 V to 0 V. The compara-
tor U10 senses this voltage change and turns off the power MOSFET switch Q10
and the power to the backlight inverter board.
The potentiometer R301 could be used to dim the LCD backlight brightness. But
R302 is not installed, so the adjustment has no effect and the backlight is at
maximum brightness.
There are two USB connectors on the board that are connected through a cable to
the USB 2.0 interface connector on the CPU board.
Keypad Board
The Keypad board contains the switch patterns for the elastomer keys and the
front-panel LEDs. The board is connected to the Front-Panel Processor board by
the board-to-board connectors J10 and J11.
A40 AC Distributor Board
The A40 AC Distributor board supplies standby power (5VSB) to the SBC and
the ATX power control circuit on the A20 Backplane board.
RF Matching Attenuator
Front-panel Keypad
Interface and LED Control
LVDS Data for LCD
Backlight Power Control
LCD Brightness Control
USB Ports