Frequency Synthesizer Circuits; Voltage Block Diagram - Icom IC-M400BB Service Manual

July 2013
4-3 FREQUENCY SYNTHESIZER
• VCO (VCO UNIT)
The VCO (Q3, Q4, and D1–D3) generates both 1st LO signal
for MAIN channels and the TX signal.
The output of buffer (Q7) is used as the TX or RX LO signal.
While receiving, the LO signal is applied to the 1st IF mix-
er for MAIN channels (MAIN UNIT: Q202), through the LO
SW (MAIN UNIT: D8) and LPF (MAIN UNIT: L206, L207 and
C262).
While transmitting, the LO signal is applied to the TX AMP
circuits, through the LO SW (MAIN UNIT: D7).
• FREQUENCY SYNTHESIZER CIRCUIT
IC201
IF IC
IC101
21.25MHz
X101 PLL
MAIN UNIT
LOOP
FILTER
Q2,Q8
D1,D2
MOD SHIFT
From the TX AF circuits

4-4 VOLTAGE BLOCK DIAGRAM

Voltage from the power supply is routed throughout the transceiver, through regulators and switches.
Q511,Q512
HV
Power PWR
supply CTRL
MAIN UNIT
LOGIC UNIT
IC4
3.3 V
REG
Q6
Q7
BUFF BUFF
VCO UNIT
Q3,Q4
Q5
D3
VCO
BUFF
IC512 Q10,Q11
VCC +5 V 5V
REG CTRL
IC511
+3 V
Q21,Q22
R8 R8V Receive
circuits
REG
L3V
CPU
• PLL (MAIN UNIT)
A portion of VCO output signal is passed through two buffers
(VCO UNIT: Q5 and Q6), and then fed back to the PLL IC
(IC101, pin 16).
The PLL IC (IC101) phase-compares the outputs of the refer-
ence frequency oscillator (TCXO; X101) and VCO, and the
phase-difference is output as the charge pump current.
The current is passed though the loop fi lter (R1–R3, C1–C3,
and C10) to be converted into the lock voltage, which controls
the oscillating frequency of VCO.
When the oscillation frequency drifts, its phase changes from
that of the reference frequency, causing a lock voltage change
to compensate for the drift in the VCO oscillating frequency.
Q202
1st mixer
(MAIN CH)
D7,D8
To the TX AMP circuits
TX/RX
SW
T5
T5V
Q12,Q23,Q24
3V
R3
R3V
REG CTRL
IC903
+1.1 V
REG
4-4
Transmit circuits
Receive circuits
Noise canceller