Frequency Synthesizer Circuits; Main Unit - Icom ID-51E User Manual

4-3 FREQUENCY SYNTHESIZER CIRCUIT

(MAIN UNIT)

VCOs
The ID-51A/E has total of four VCOs; two VCOs for band A
and another two for band B.
• Band A
VHF VCO (VCO1 UNIT)
The VHF VCO (Q311, D304–D306) generates both 1st LO
signal (for receiving a VHF signal on band A) and the VHF
TX signal. The output of buffer (Q200) is amplifi ed by the LO
AMP (Q201), and then used as the VHF TX/RX LO signal.
While receiving, the LO signal is applied to the 1st IF mixer
(Q820) for receiving a signal on the VHF band, through the
RF SW (D821).
While transmitting, the LO signal is applied to the TX AMP
circuits, through the LO SW (D14).
UHF VCO (VCO1 UNIT)
The UHF VCO (Q27, D10–D12) generates both 1st LO signal
(for receiving a UHF signal on band A) and the UHF TX sig-
nal. The output of buffer (Q200) is amplifi ed by the LO AMP
(Q201), and then used as the UHF TX/RX LO signal.
While receiving, the LO signal is applied to the 1st IF mixer
(Q801) for receiving a signal on the UHF band, through the
RF SW (D802).
While transmitting, the LO signal is applied to the TX AMP
circuits, through the LO SW (D14).
• Band B
VHF VCO (VCO2 UNIT)
The VHF VCO (Q311, D304–D306) generates the 1st LO
signal (for receiving a VHF signal on band B). The output of
buffer (Q200) is amplifi ed by the LO AMP (Q201), and then
used as the 1st LO signal.
While receiving, the LO signal is applied to the 1st IF mixer
(MAIN UNIT: Q830) for receiving a signal on the VHF band,
through the RF SW (MAIN UNIT: D831).
• FREQUENCY SYNTHESIZER CIRCUIT
X1
REFMOD
15.3MHz
VCOMOD
VHF
VCO
Q311,
D304,D305,D306
LOOP
IC6
FIL
Q27,
PLL
D10,D11,D12
IC
UHF
VCO
FIN
LPF
Q311,D304,D305,D306
VHF
VCO
IC450
PLL LOOP
IC FIL
Q27,D10,D11,D12
UHF
VCO
FIN
LPF
UHF VCO (VCO1 UNIT)
The UHF VCO (Q27, D10–D12) generates 1st LO signal
(for receiving a UHF signal on band B). The output of buffer
(Q200) is amplifi ed by the LO AMP (Q201), and then used as
the UHF TX/RX LO signal.
While receiving, the LO signal is applied to the 1st IF mixer
(MAIN UNIT: Q811) for receiving a signal on the UHF band,
through the RF SW (MAIN UNIT: D812).
PLL
• Band A
A portion of VHF and UHF VCOs output signal is amplifi ed
by two buffers (VCO1 UNIT: Q200 and Q202) and passed
through the LPF (VCO1 UNIT: L202, C209 to C211), and
then fed back to the PLL IC (IC6, pin 8).
The PLL IC (IC6) phase-compares the output of reference
frequency oscillator (TCXO; X1) and VCO, and the phase dif-
ference is output as the charge pump current. The current is
passed though the loop fi lter (R67, R71, R90, R93, C91, C92,
C96 and C102) 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.
Band B
A portion of VHF and UHF VCOs output signal is amplifi ed
by two buffers (VCO2 UNIT: Q200 and Q202) and passed
through the LPF (VCO2 UNIT: L202, C209 to C211), and
then fed back to the PLL IC (IC6, pin 8).
The PLL IC (IC6) phase-compares the output of reference
frequency oscillator (TCXO; X1) and VCO, and the phase dif-
ference is output as the charge pump current. The current
is passed though the loop fi lter (R452, R454, R455, R457,
C455, C457 to C460) 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.
Q200 Q201
LO A_LOOUT
BUFF
AMP
Q202
BUFF
VCO1 UNIT
B_LO
LO
BUFF
AMP
Q200 Q201
AMP
VCO2 UNIT
Q202
4 - 7
D14
LO
TX AMP circuit. ->
SW
A_LO
Q820
VHF 1st LO
RF
SW
UHF 1st LO
D802,D821
Q801
Q830
D812,D831
VHF 1st LO
RF
SW
UHF 1st LO
Q811