Fluke PM6681 - Page 46

•
Prescaler
4.5
GHz, PM
9625
Limiter
Figure
4-32
PM 9625 Block diagram.
The PM
9625
prescaler cannot
be
repaired at a
local
workshop. It must be sent to the
factory
for repair.
The prescaler consists
of the following
parts,
(see Figure
4-
32):
-
The limiter
consists
of a 6 dB
attenuator and a PiN
diode
attenuator,
to achieve
constant input
amplitude
to the
amplifiers.
Amplifier
-
The
amplifier
consists of 4
cascade coupled
integrated
GaAs amplifiers:
each amplifies
approximately
8
dB.
First
divider
“
The
GaAs
divider chip
consists
of an input
buffer,
3 divi-
der stages, and
2 output buffer
stages. The
circuit
divi-
des by
8.
Second
divider
“
This
divider divides the
signal from the first
divider by 4.
In
total the frequency
is divided by
32,
and the
output
frequency
from the
prescaler is 155 MHz at
maximum.
Voltage
regulators
-
Two
positive
voltage
regulators
are used for the
GaAs
amplifier
and
the first divider.
4-22
Hardware
Functional
Description