Icom IC-F3GS, IC-F3GT service manual PLL Circuit, Power Supply Circuits Voltage Line

The signal output from the power detector circuit (D32, D33) is applied to the differential amplifier (IC3a, pin 2), and the “T4” signal from the expander (IC10, pin 11), controlled by the CPU (IC8), is applied to the other input for reference.

When the driving current is increased, input voltage of the differential amplifier (pin 2) will be increased. In such cases, the differential amplifier output voltage (pin 1) is decreased to reduce the driving current.

4-3 PLL CIRCUIT

A PLL circuit provides stable oscillation of the transmit fre- quency and receive 1st LO frequency. The PLL output com- pares the phase of the divided VCO frequency to the refer- ence frequency. The PLL output frequency is controlled by the divided ratio (N-data) of a programmable divider.

The PLL circuit contains the VCO circuit (Q7, Q8). The oscil- lated signal is amplified at the buffer-amplifiers (Q6, Q5) and then applied to the PLL IC (IC1, pin 2).

The PLL IC contains a prescaler, programmable counter, programmable divider and phase detector, etc. The entered signal is divided at the prescaler and programmable counter section by the N-data ratio from the CPU. The divided signal is detected on phase at the phase detector using the refer- ence frequency.

If the oscillated signal drifts, its phase changes from that of the reference frequency, causing a lock voltage change to compensate for the drift in the oscillated frequency.

A portion of the VCO signal is amplified at the buffer-ampli- fier (Q4) and is then applied to the receive 1st mixer (Q13) or transmit buffer-amplifier circuit (Q3) via the T/R switching diode (D3, D4).

• PLL circuit

4-4 POWER SUPPLY CIRCUITS VOLTAGE LINE

LINE	DESCRIPTION
HV	The voltage from the attached battery pack.
	The same voltage as the HV line (battery volt-
VCC	age) which is controlled by the power swtich
	([VOL] control).
	Common 5 V converted from the VCC line by the
5V	reference regulator circuit (IC6). The output volt-
	age is applied to the 5 V regulator circuit (Q18,
	Q19).
T5	5 V for transmitter circuits regulated by the T5
	regulator circuit (Q22).
R5	5 V for receiver circuits regulated by the R5 reg-
	ulator circuit (Q21).
S5	Common 5 V converted from the VCC line by the
	S5 regulator circuit (Q18, Q19).
	The same voltage as the 5V line for the optional
OPT	HM-46L, EM-71 or HS-51 through a resistor
	(R132).
	The same voltage as the 5V line which is regu-
CPU5	lated by +5 V CPU regulator circuit (IC6). The
	voltage is applied to the reset circuit (IC11) and
	CPU (IC8).

"DEV" signal from the

D/A convertor (IC10, pin 22) when transmitting

Loop

filter

VCO circuit

Q7, Q8

Buffer Q6

Buffer

Q4

Buffer

Q5

D3

to transmitter circuit

to 1st mixer circuit D4

30.6MHz signal to the FM IF IC

8		Phase	Programmable		Prescaler	2
		detector	counter
17		Programmable				3	PLST
	⋅2			Shift register		4
							SCK
		divider				5
							SO
		16

X1

15.3 MHz

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