Pll Circuit; Control Circuit; Cpu - HYT TM-610 Service Manual

TM-610 Service Manual

4. PLL Circuit

The frequencies of receiving the first local oscillator signal and transmitting signal are generated by the PLL circuit. The
PLL circuit consists of Tx frequency oscillator (Q701), Rx frequency oscillator (Q702), buffer amplifier (Q703), RF amplifier
(Q102), PLL IC (IC801), LPF and Tx/Rx VCO control switch (Q704, Q706).
In transmit mode, IC120 transmits the frequency data to PLL IC. Q704 is turned on to activate Tx VCO. The output signal
is amplified by Q703 and Q102, and then divided by PLL IC into 2.5KHz, 5KHz or 6.25KHz signals. The divided signal is
compared with the 2.5KHz, 5KHz or 6.25KHz reference signal from a 16.8MHz crystal oscillator (2.5 PPM frequency
stability) in the phase comparator. The frequency control voltage output from the phase comparator is sent to Tx VCO after
passing through LPF (Q802, Q803). In the meantime, the modulation signal (Tx) is passed to Tx VCO for frequency
modulation.
The working principle in receive mode is similar to that in transmit mode.
Figure 3

5. Control Circuit

The control circuit is composed of CPU, reset IC and power supply control circuit.

5.1 CPU

IC502 (CPU) operates at 9.8304MHz. CPU controls the data transmission among E2PROM (IC501), Rx circuit, Tx circuit,
control circuit, display circuit and peripheral circuits.
Figure 4 Control Circuit
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