Voltage-Controlled Oscillator (Vco); Vco Block Diagram - Motorola HT Series Detailed Service Manual

12
The loop filter which consist of C231, C232, C233, R231, R232 and R233 provides the necessary dc
steering voltage for the VCO and determines the amount of noise and spur passing through.
In achieving fast locking for the synthesizer, an internal adapt charge pump provides higher current
at pin 45 of U201 to put synthesizer within the lock range. The required frequency is then locked by
normal mode charge pump at pin 43.
Both the normal and adapt charge pumps get their supply from the capacitive voltage multiplier
which is made up of C258, C259, C228, triple diode CR201 and level shifters U210 and U211. Two
3.3V square waves (180 degrees out of phase) are first shifted to 5V, then along with regulated 5V,
put through arrays of diodes and capacitors to build up 13.3V at pin 47 of U201.
1.5

Voltage-Controlled Oscillator (VCO)

(Refer to the UHF Voltage-Controlled Oscillator Schematic Diagram on
Rx-SW
Tx-SW
(U201 Pin28)
VSF
Steer Line
Voltage
(VCTRL)
RX VCO
RX Tank
Circuit
TX VCO
TX Tank
Circuit
December 26, 2003
Pin 20
Pin7
TX/RX/BS
Pin13
Switching Network
Vcc-Superfilter
Pin3
Collector/RF in
Pin4
RX
Rx
Active Bias
Pin5
Pin6
TX
Tx
Active Bias
Pin16
Pin15
Vsens
Circuit
Pin18
Vcc-Logic
VSF
(U201 Pin28)
Figure 1-5. VCO Block Diagram
UHF Theory of Operation: Voltage-Controlled Oscillator (VCO)
Level Shifter
Network
Prescaler Out
TRB_IN
Pin 19 Pin 12
Presc
U241
VCOBIC
RX
Pin8
Pin14
TX
Pin10
Pin2 Pin1 Pins 9,11,17
Tx-I adjust
Rx-I adjust
page 23.)
5V
AUX3 (U201 Pin2)
AUX4 (U201 Pin3)
U201 Pin 32
LO RF INJECTION
Second
Low Pass
Buffer
Filter
VSF
(U201 Pin28)
VCC Buffers
TX RF Injection
Attenuator
FMR-2045A-2