Filter
Top Products
AlOA4
AlOA4
Phase
Lock
Loop
3
(PLL3)
Up
Converter,
Circuit
Description
The function of AlOA4 is to mix 160 MHz with the output of AlOA5 (.15 to 6 MHz),
up-converting that output by 160 MHz. The two frequencies are mixed together in a phase
lock loop which has a closed loop bandwidth of approximately 10 kHz.
Frequency
Multiplier
x
1.6
@
The frequency multiplier generates 160 MHz from the 100 MHz at the input. U3 divides the
input by 5 and produces harmonics of the resulting 20 MHz. The 160 MHz
bandpass
filter
selects 160 MHz, which is then amplified by Q5 and buffered with a pad to -20
dBm.
All
three adjustments are set by peaking the 160 MHz signal.
160
to
166
MHz
VCO
@
The 160 to 166 MHz VCO uses
Ql
in a Colpitts configuration.
Lll
centers the frequency
range of the VCO while CR3 is the varactor which tunes the oscillator.
Q2
and Q4 are buffer
amplifiers.
Mixer
@
U7 is a double-balanced mixer which operates with about
f7
dBm
of LO power at 160 to
166 MHz and -20
dBm
of RF signal power at 160 MHz. The desired output is the difference
frequency which falls in the range between 150 kHz and 6 MHz.
IF
Amplifier
@
The output of the mixer U7 is filtered by an 8-section elliptic filter which must reject
14 to 20 MHz, and other higher frequencies.
The filter output is amplified by Q3.
Loop
Amplifier
@
The phase detector outputs are connected to the differential inputs of U2.
C9
and R16
provide ac feedback around U2 while dc feedback is provided by the entire phase lock loop.
CR4 and CR5 lessen the charging time of C7 when the input frequency is changed abruptly.
R14, R15, and C7 form an ac voltage divider which sets the loop bandwidth to about 10
kIIz.
The output of the divider goes to the varactor in the oscillator and tunes the VCO.
UlB
prevents this tune voltage from latching at a positive value by sensing when the voltage goes
above 0 V. When this occurs, the output of
UlB
pulls the tune voltage down to the proper
lock range. R13 provides hysteresis to allow time for the loop to lock.
AlOA4
1