Circuit Operation Of Rf Unit - Panasonic KX-F900 Service Manual

I KX-F900 I
13-5. CIRCUIT OPERATION OF RF UNIT
(1) PLL Circuit
The PLL IC comprises two PLL blocks, one for transmission and one for reception, a transmission multiplier
circuit, and a reception first mixer circuit.
The 900 MHz band frequency from the RX VCO, the 450 MHz band frequency from the TX VCO, and the
10.25 MHz reference oscillator frequency are frequency divided by a frequency divider controlled by the CPU
to create the 12.5 kHz comparison frequency. The phase comparator determines the phase difference be-
tween the TX and RX frequencies and the reference frequency, and supplies a control voltage via pin 7 or pin
18 to the appropriate VCOs so that the desired TX and RX frequencies are maintained.
The output from the TX VCO is multiplied by 2 internally by the IC, resulting in a 900 MHz band signal that is
then output to pin 2. Also, the RX VCO signal is supplied to the first mixer built into the IC.
Circuit Diagram
i
Buffer
_k--'-<_2. Multiplier[
TXVCO_ [_ Divider I
, Buffer
Phase
, Comparator
1 . _ StandardJ .I T
o oi,,a,e
', Buffer
I '@
M,XER,.PUT
Divider _ RXVCO
,_ Buffer
Phase
T
Comparator (_
T
Divider I
MIXER OUTPUT
_)<---- RST }
_<--- SI from CPU
_<---- CPS
(2) TX VCO, RX VCO
TX VCO and RX VCO are module as shown below table.
Pin Layout
Oscillator
Frequency
TXVCO RXVCO
MOD GND OUT
t__J ', . ... ', %_;
E ]
I
'---I ;.... : "H:I
CONTROL GND BiAS
VOLTAGE VOLTAGE
Shield Case side View
Portable Handset 463.05~463.775MHZ
Base Unit 451.05~451.775MHZ
MOD GND OUT
,__.; ', . ... ', ,__;
E 3
l---i _.... i _---t
CONTROL GND BIAS
VOLTAGE VOLTAGE
Shield Case side View
Portable Handset 891.4N892.85MHZ
Base Unit 936.8~938.25MHZ
Output -6dB +2dB
Level
Control 0.5-2.5V DC
Voltage
- 175--
o
o
C:
--I
0
"1o
m
_0
_>
.-I
0
Z