Circuit Description; Pll Frequency Synthesizer; Pll; Vco - HYT TC-610 Service Manual

Circuit Description

Realization Methods for Basic Functional Modules

PLL Frequency Synthesizer

The PLL circuit mainly generates the local oscillator signal for reception and the RF carrier signal for
transmission. It consists of the VCO oscillator circuit and baseband processor and enables frequency
tracking and channel change under the control of MCU signal.
1.

PLL

MB95F108AK
WPFV-GE1
The step frequency of the PLL circuit is 5.0KHz, 6.25KHz, 10.0KHz or 12.5KHz. Therefore, the
reference oscillator signal (38.4MHz) is divided into 5.0KHz, 6.25KHz, 10.0KHz or 12.5KHz reference
frequency by a fixed counter at U202 in PLL. The output signal from VCO passes through buffer Q102
followed by amplifier Q103 and enters U202 in PLL for frequency division by a variable divider. The
signal derived from the frequency division is compared with the reference frequency at the phase
comparator PD in PLL. Then the output signal from the phase comparator is filtered by a low-pass filter
and passed to varactors D100, D101, D102 and D103 of VCO, to control the output frequency.
2.

VCO

The VCO section is realized by the oscillator circuit of three-point capacitance.
The oscillator frequency of VCO is generated by Q100 in transmit mode and by Q101 in receive mode.
U202 generates a control voltage via the phase comparator to control varactors (D100 and D101 in
transmit mode; D102 and D103 in receive mode), so that the oscillator frequency of VCO is made
consistent with the preset frequency in MCU within a broader frequency range.
Transistor Q652 toggles between transmit and receive modes under the control of T/R. In transmit mode,
T/R is set to low level, causing Q653 to be on and Q100 to operate. In receive mode, T/R is set to high
Q5
BUFFER
APC/TUNE
U605
1
Q6
1
D100
L101
D104
D101
D102
Q101
2SK508NV
L102
D103
12.8MHZ
LPF
1/2 CP OSC
EN
DATA
U202
32/33 1/2
CLK
17bitDIV
21bitDIV
Figure 2
12
TC-610/620 Service Manual
Q100
2SK508NV
TX-VCO
T/R-SW
RX-VCO