Block Diagram Description
General
The PM6690 Timer/Counter consists of three main units:
–
Front unit
–
Main printed circuit board
–
Rear panel unit
Several options exist:
–
Prescalers on separate PCBs covering different fre
-
quency ranges (3 GHz and 8 GHz)
–
Two OCXO timebases (very high & ultra-high stability)
– Rackmount kit
The chassis of the counter consists of a front piece molded in
aluminum, an aluminum rear panel, and two extruded alumi-
num bars that hold the front and rear panels together. This unit
can be slid into the aluminum cover of the instrument.
The main circuit board is fixed to the two bars. The display
circuit board is fixed to the front piece. A detachable connec-
tor joins the electronics of the front unit and the main board,
and the molded front piece is fixed with screws to the two alu-
minum bars. The rear panel is also fixed to the bars with
screws.
The front unit contains all functions needed for the user com
-
munication: keyboard, display and input BNCs. All other
electrical functions are on the main board. The rear panel has
no PCB. The connectors here are all soldered directly to the
main circuit board.
Block Diagram
Figure 4-1 contains a block diagram of the electrical functions
of the counter. They are divided among the main circuit board,
the display board, the rear panel and the optional prescaler
board. See the schematic diagrams in Chapter 9 for complete
information.
Most functions are placed on the main board:
–
Input amplifiers with trigger level circuits
– Power supply
– Measurement logic
– Microcomputer circuitry
– GPIB interface
– USB interface
– External reference input
– External arming input
The rear panel unit is made of aluminum with a number of
mounted connectors, a fan and a power line inlet with filter.
Most connectors are soldered directly to the main board.
NOTE: Schematic diagrams in this chapter are simplified.
For complete information, see Chapter 9.
4-4 Block Diagram Description
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