Motorola GP series Detailed Service Manual

1-8 THEORY OF OPERATION
4.2 Voltage Controlled Oscillator (VCO)
(Refer to Figure 2-5 and the 800 MHz Voltage Controlled Oscillator schematic diagram)
The VCOBIC (U250) in conjunction with the Fractional-N synthesizer (U201) generates RF in both
the receive and the transmit modes of operation. The TRB line (U250 pin 19) determines which
oscillator and buffer will be enabled. A sample of the RF signal from the enabled oscillator is routed
from U250 pin 12, through a low pass filter, to the prescaler input (U201 pin 32). After frequency
comparison in the synthesizer, a resultant CONTROL VOLTAGE is received at the VCO. This
voltage is a DC voltage between 2.0V (low frequency) and 11.0V (high frequency) when the PLL is
locked on frequency.
The VCOBIC(U250) is operated at 4.54 V (VSF) and Fractional-N synthesizer (U201) at 3.3V. This
difference in operating voltage requires a level shifter consisting of Q200 and Q252 on the TRB line.
Figure 1-5 UHF VCO Block Diagram
The operation logic is shown in Table 2-1.
Presc
RX
TX
Injection
Amplifier
Buffer
Amplifier
Pin 8
Pin 14
Pin 10
5V
(U201 Pin 28)
VCC Buffers
TX RF Injection
U201 Pin 32
AUX4 (U201 Pin 3)
AUX3 (U201 Pin 2)
Prescaler Out
Pin 12
Pin 19
Pin 20
TX/RX/BS
Switching Network
U250
VCOBIC
Rx Active
Bias
Tx Active
Bias
Pin 2
Rx-I adjust
Pin 1
Tx-I adjust
Pins 9,11,17
Pin 18
Vsens
Circuit
Pin 15
Pin 16
TX VCO
Circuit
TX
Tank
RX VCO
Circuit
RX
Tank
Pin 7
Vcc-Superfilter
Collector/RF in
Pin 4
Pin 5
Pin 6
RX
TX
(U201 Pin 28)
Rx-SW
Tx-SW
Vcc-Logic
(U201 Pin 28)
Steer Line
Voltage
(VCTRL)
Pin 13
Pin 3
TRB_IN
LO RF INJECTION
Level Shifter
Network
VSF
VSF
VSF

Motorola GP series Specifications

General

Brand	Motorola
Model	GP series
Category	Radio
Language	English