Voltage Controlled Oscillator (Vco) - Motorola CDM Series Detailed Service Manual

VHF (136–174 MHz) 1–25W Frequency Synthesis
circuitry (D3201, C3202, C3203). This voltage multiplier is basically a diode capacitor network driven
by two (1.05MHz) 180 degrees out of phase signals (U3201-14 and -15).
Output LOCK (U3201-4) provides information about the lock status of the synthesizer loop. A high
level at this output indicates a stable loop. IC U3201 provides the 16.8 MHz reference frequency at
pin 19.
The serial interface (SRL) is connected to the µP via the data line DATA (U3201-7), clock line
CLK (U3201-8), and chip enable line CSX (U3201-9).
4.3

Voltage Controlled Oscillator (VCO)

The Voltage Controlled Oscillator (VCO) consists of the VCO/Buffer IC (VCOBIC, U3301), the TX
and RX tank circuits, the external RX buffer stages, and the modulation circuitry.
Rx-SW
Tx-SW
(U3201 Pin28)
Steer Line
Voltage
(VCTRL)
RX VCO
Circuit
RX Tank
Q3304
TX VCO
TX Tank
Circuit
The VCOBIC together with the Fractional-N synthesizer (U3201) generates the required frequencies
in both the transmit and receive modes. The TRB line (U3301 pin 19) determines which tank circuits
and internal buffers are to be enabled. A high level on TRB enables the TX tank and TX output (pin
10), and a low enables the RX tank and RX output (pin 8). A sample of the signal from the enabled
RF output is routed from U3301 pin 12 (PRESC_OUT), via a low-pass filter, to pin 32 of
U3201 (PREIN).
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
(U3211 Pin1)
Figure 4-4 VHF VCO Block Diagram
AUX3 (U3201 Pin2)
Prescaler Out
TRB IN
Pin 19 Pin 12
Presc
U3301
VCOBIC
RX
Pin8
Pin14
TX
Pin10
Pin2 Pin1 Pins 9,11,17
Tx-I adjust
Rx-I adjust
Section 4: 2-7
U3201 Pin 32
LO RF INJECTION
Matching
Low-Pass
Network
Filter
Q3301
(U3211 Pin1)
VCC Buffers
TX RF Injection
Attenuator
6881091C63-F