User's Manual

OWDTR-0006-E Exhibit 8 Com-Net Ericsson
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1 Reference Oscillator
h
e reference oscillator consists of a 1.5ppm TCXO (Temperature Controlled Compensated Crysta
l
O
scillator). The standard of reference oscillator frequency is 19.2MHz.
h
e TCXO is enclosed in a RF shielded can. The TCXO is compensated by internal temperatur
e
o
mpensated circuit for both low and high temperature. With no additional compensated the oscillator wil
l
r
ovide 1.5 PPM stability from -30°C to +60°C.
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2 PLL Frequency Synthesizer chip
L
L Frequency Synthesizer chip U305 contains a programmable reference oscillator divider(R), prescaler
,
h
ase detector, and programmable VCO dividers (+N, A).
h
e reference frequency 19.2MHz from the reference oscillator is divided by a fixed integer number t
o
b
tain a 6.25KHz or 3.125KHz channel reference for the synthesizer. This divide value can be changed b
y
C
PROGRAMMER.
h
e internal phase detector compares the output of the reference divider with the output of internal counter
.
h
e count counter receives as its input the VCO frequency divided by the Prescaler and programmed by th
e
m
icrocomputer.
h
is results in an error voltage when the phase differ and a constant output voltage when phase-detector inpu
t
o
mpare in frequency and phase. If a phase error is detected, an error voltage is developed and applied to th
e
V
CO DC offset and loop filter to reset the VCO frequency. The count of the +N, A counters is controlled b
y
h
e frequency data received on the SC.CLK, SC.DATA - and SC.SYN1LE- line from the microcomputer.
W
hen a different channel is selected or when changing to the transmit or receive mode an error voltage i
s
e
nerated and appears at the phase-detector output, causing the Phase Locked Loop to acquire the ne
w
r
equency.
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3 Loop filter
h
e Loop filter consists of R314 through R319 and C321 through C326. This filter controls the bandwidt
h
n
d stability of the synthesizer loop.
W
hen a different channel changing or changing to the transmit or receive mode, analog switch is controlle
d
y
VCO RX/TX for PLL lock up first.
h
e output of the filter is applied to the varicaps in the transmit and receive VCO to adjust and maintain th
e
V
CO frequency. The use of to VCO allows rapid independent selection of transmit and receive frequencie
s
c
ross the frequency split.
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4 Rx VCO
h
e Rx VCO consists of low-noise silicon transistor oscillator, and followed by high-gain buffer.
h
e VCO is switched on and off VCO RX/TX line. When VCO RX/TX is low, the Rx VCO is turned on
,
ansistor Q301 is on. The Rx VCO output is typically 0dBm. The output is applied to the PLL Frequenc
y
y
nthesizer chip for VCO frequency control and as the Receiver frequency to Rx 1’st Mixer through the 1’s
t
ocal oscillator buffer amplifier. The VCO voltage need only be set once at some frequency of the band an
d
p
lit, after which it operates over the entire split with no additional tuning.
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5 Tx VCO
h
e Tx VCO is basically the same as the Rx VCO. The VCO consists of silicon transistor oscillator followe
d
y
high-gain buffer amplifier. When VCO RX/TX is high, the Tx VCO is turned on, transistor Q302 is on.
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6 Lock Detect
h
e Lock Detect signal is outputted from synthesizer IC (U305-18). The LOCK(U305-18) is low if a larg
e
r
equency error exist, and will carry unlock condition to the microcomputer.