Section 6: 2-8 UHF Band 2 (450–512/527 MHz) 1–25 W Frequency Synthesis
6881091C63-F
4.3 Voltage Controlled Oscillator (VCO)
The Voltage Controlled Oscillator (VCO) consists of the VCO/Buffer IC (VCOBIC, U5301), the TX
and RX tank circuits, the external RX buffer stages, and the modulation circuitry.
Figure 6-4 UHF VCO Block Diagram
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, to pin 32 of U5201 (PREIN).
A steering line voltage (VCTRL) between 3.0V and 10.0V at varactor diode CR5311 will tune the full
TX frequency range (TXINJ) from 450 MHz to 512 (or 527) MHz, and at varactor diodes CR5301,
CR5302 and CR5303 will tune the full RX frequency range (RXINJ) from 405 MHz to 482 MHz. The
tank circuits uses the Hartley configuration for wider bandwidth. For the RX tank circuit, an external
transistor Q5301 is used in conjunction with the internal transistor for better side-band noise.
Similarly, an external transistor Q5311 is used in the TX tank circuit.
Presc
RX
TX
Matching
Network
Low-Pass
Filter
Attenuator
Pin8
Pin14
Pin10
(U5201 Pin28)
VCC Buffers
TX RF Injection
U5201 Pin 32
AUX3 (U5201 Pin 2)
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 Pin 28)
Rx-SW
Tx-SW
Vcc-Logic
(U5201 Pin 28)
Steer Line
Voltage
(VCTRL)
Pin13
Pin3
TRB IN
LO RF INJECTION
Q5301
Q5332
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