Motorola HT Series User Manual

5-6 UHF Band 2 Theory of Operation: Voltage-Controlled Oscillator (VCO)
The loop filter, which consists 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 the 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
3.3 V square waves (180 deg out of phase) are first shifted to 5 V, then along with regulated 5 V, put
through arrays of diodes and capacitors to build up 13.3 V at pin 47 of U201.
5.5 Voltage-Controlled Oscillator (VCO)
(Refer to the UHF Voltage Controlled Oscillator Schematic Diagram on page 9-221.
Figure 5-5. VCO Block Diagram
Presc
RX
TX
Matching
Network
Low Pass
Filter
Attenuator
Pin8
Pin14
Pin10
Level Shifter
Network
5V
(U201 Pin28)
VCC Buffers
TX RF Injection
U201 Pin 32
AUX4 (U201 Pin3)
AUX3 (U201 Pin2)
Prescaler Out
Pin 12Pin 19
Pin 20
TX/RX/BS
Switching Network
U241
VCOBIC
Rx
Active Bias
Tx
Active Bias
Pin2
Rx-I adjust
Pin1
Tx-I adjust
Pins 9,11,17
Pin18
Vsens
Circuit
Pin15
Pin16
RX VCO
Circuit
TX VCO
Circuit
RX Tank
TX Tank
Pin7
Vcc-Superfilter
Collector/RF in
Pin4
Pin5
Pin6
RX
TX
(U201 Pin28)
Rx-SW
Tx-SW
Vcc-Logic
(U201 Pin28)
Steer Line
Voltage
(VCTRL)
Pin13
Pin3
TRB_IN
LO RF INJECTION
VSF
VSF
VSF

Motorola HT Series Specifications

General

Brand	Motorola
Model	HT Series
Category	Two-Way Radio
Language	English