2-30
Theory of Operation
A steering line voltage (VCTRL} between 3.0V and 1
O.OV
at varactor diode CR3303 will tune the full
TX frequency range (TXINJ) from 746 MHz to 794 MHz, and at varactor diodes CR3301 and
CR3302 will tune the full RX frequency range (RXINJ) from 819 MHz to 837 MHz. The tank circuits
uses the Hartley configuration for wider bandwidth. External VCO transistors (03305, TX and
03306,
RX) are used for lower noise.
AUX3
(U4201
Pin2)
TRB
IN
Prescaler Out
r----I~U4201
Pin
32
Pin20
Pin
19
Pin
12
~-SW~--~~
P
:
in7
~-----f------::
~~--~--,
TX/RX/BS
Tx-SW....
Pin13 Switching Network
LO
RF
INJECTION
Collector/RF
in
Pin4
Pin2
Pin1
Pins9,
11
,
17
Rx-1
adjust Tx-1 adjust
(U420 Pin28)
Figure 2-14. 700 MHz VCO Block Diagram
The
external RX buffers (03301-2) are enabled by a high at U3301 pin 7 via transistor switch
03303.
In TX mode the modulation signal (VCOMOD) from the LVFRAC-N synthesizer
IC
(U3201
pin 41)
is
superimposed on the steering line voltage (VCTRL) via an attenuator network (R3319-20,
C3241 and C3245).
To Next Page
Loading...
