User Manual

CIRCUIT DESCRIPTION
4-4
Part No. 001-3422-003
Figure 4-2 U811 Synthesizer Block Diagram
4.2.1 VOLTAGE-CONTROLLED OSCILLATOR
Oscillator (Q872)
The VCO is formed by Q872, several capacitors and varactor diodes, and air wound coil L872. It oscillates at
the transmit frequency in transmit mode and first injection frequency in the receive mode
(132-174 MHz in transmit and 153.45-195.45 MHz in receive).
Biasing of Q872 is provided by R873, R874 and R876. An AC voltage divider formed by C872, C874 and
C875 initiates and maintains oscillation and also matches Q872 to the tank circuit. Air wound inductor L872 is
grounded at one end to provide shunt inductance to the tank circuit.
CLOCK
DATA
STROBE
Vss
RF
IN
RF
IN
64/65/72
PRESCALER
MAIN DIVIDERS
EM
FB
2 2 12 8
PR NM1 NM3
NM2
FRACTIONAL
ACCUMULATOR
PRESCALER
MODULUS
CONTROL
3
FMOD
NF
FB
SERIAL INPUT + PROGRAM LATCHES V
DD
TEST
IN
REF
EM+EA
REFERENCE DIVIDER +2 +2 +2
MAIN
MAIN
PHASE
DETECTOR
REFERENCE
SELECT
2
SM
EM
REFERENCE
SELECT
2
SA
SECONDARY
PHASE
DETECTOR
EA
AUXILIARY
IN
EA
AUX
12
NR
12
NAPA
AUXILIARY DIVIDER
PRESCALER
1/4
NORMAL
OUTPUT
CHARGE
PUMP
OUTPUT
CHARGE
PUMP
SPEED-UP
OUTPUT
CHARGE
PUMP
INTEGRAL
OUTPUT
CHARGE
PUMP
AUXILIARY
CN
8
CL
2
CK
4
2
V
SSA
V
DDA
LOCK
PHA
RA
PHI
PHP
RN
RF