Motorola CDM Series - Page 537

UHF Band 2 (450–512/520 MHz) 25–40 W Bipolar Frequency Synthesis Section 10: 2-7
6881091C63-F
The serial interface (SRL) is connected to the µP via data line DATA (U5201-7), clock line CLK
(U5201-8), and chip enable line CSX (U5201-9).
4.3 Voltage Controlled Oscillator (VCO)
The voltage controlled oscillator (VCO), shown in Figure 10-4, consists of a VCO buffer IC
(VCOBIC, U5301), TX and RX tank circuits, external RX buffer stages, and modulation circuits.
The VCOBIC together with Fractional-N synthesizer (U5201) generates the required frequencies in
both transmit and receive modes. The TRB line (U5301, pin 19) determines which tank circuits and
internal buffers are to be enabled. A high level on TRB enables TX tank and TX output (pin 10), and
a low enables RX tank and RX output (pin 8). A sample of the signal from the enabled output is
routed from U5301, pin 12 (PRESC_OUT), via a low-pass filter of U5201, pin 32 (PREIN).
A steering line voltage (VCTRL) between 3.0V and 10.0V at varactor diode CR5311 tunes the full TX
frequency range (TXINJ) from 450 MHz to 512 (or 520) MHz, and at varactor diodes CR5301,
CR5302, and CR5303 tunes the full RX frequency range (RXINJ) from 405 MHz to 475 MHz. The
tank circuits uses the Hartley configuration for wider bandwidth. For the RX tank circuit, external
transistor Q5301 is used in conjunction with the internal transistor for better side-band noise.
Figure 10-4 UHF VCO Block Diagram
Presc
RX
TX
Matching
Network
Low-Pass
Filter
Attenuator
Pin8
Pin14
Pin10
(U5201 Pin28)
VCC Buffers
TX RF Injection
U5201 Pin 32
AUX3 (U5201 Pin2)
Prescaler Out
Pin 12Pin 19
Pin 20
TX/RX/BS
Switching Network
U5301
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
(U5201 Pin28)
Rx-SW
Tx-SW
Vcc-Logic
(U5201 Pin28)
Steer Line
Voltage
(VCTRL)
Pin13
Pin3
TRB IN
LO RF INJECTION
Q4301
Q4332