Mic Amp And A/D Converter; Modulation And D/A Converter - Icom IC-7300 Service Manual

(2) TRANSMIT SIGNAL PROCESSING

• MIC AMP and A/D converter

The audio signal from the [MIC] connector on the front panel
is amplifi ed by the MIC amplifi er (IC1002), and then applied
to the A/D converter (IC1001) to be converted into a digital
signal. The audio signal from the [ACC] socket is applied to
the A/D converter (IC1001), through the mute SW (IC1003)
and LPF (IC1002), and is also converted into a digital sig-
nal. The converted digital signal is then applied to the DSP
(IC901) for audio processing.

• Modulation and D/A converter

The signal is digitally modulated in the DSP (IC901), result-
ing in the 36 kHz transmit IF signal, and then applied to the
FPGA (IC1351).
The audio signal from the microphone has been converted
into a digital data stream by the A/D converter. The converted
data is applied to the DSP (IC901), and digitally processed,
resulting in a modulated 36 kHz transmit IF signal.
• MAIN UNIT (Transmit circuits)
J1302
1.8V
2.GND
3.HSEND
4.START
5.BAND
6.ALC
7.NC
[ACC]
8.14V
9.KEY
10.FSKK
10
11.MOD 11
12
12.AF
13
13.SQLS
MIC UNIT
GND
AF OUT
+8V
PTT
SQL
TX signal
MIC U/D
RX signal
• FPGA BLOCK DIAGRAM (Transmit circuits)
MIC
A/D
MIC
AMP
1
2
3
4
5
6
7
FPX_AGC/FPX_DET/FPR_MOD
8
/FPCAL/BCLK/FRM/MCLK
9
IC1001
IC1003 IC1002
AMOD
LPF
IC1002
DISPLAY UNIT
MICI MIC
AMP
J1
MICE
MIC
1 7
2 8 6
3 5
4
DSP (IC901)
36 kHz
36 kHz
Transmit IF
BPF
BPF MOD
• FPGA
The transmit IF signal is applied to the FPGA (IC1351). The
FPGA mathematically processes the signal to digitally obtain
the oscillation (TX LO) and mixing (Image rejection mixer), as
if the signal is processed in a hardware up conversion circuit.
The processed signal is applied to the D/A converter to be
converted in to an analog RF transmit signal.
• RF signal processing
The transmit signal, that is processed and up-converted in
the FPGA (IC1351), is applied to the D/A converter (IC1331)
to be converted into an analog transmit signal. The transmit
signal is passed through the LPF (L1281, L1282, C1281,
C1283 and C1285), which attenuates unwanted frequency
components in the transmit signal, and is then applied to the
RF UNIT.
IC1351
IC901
DACLK
IF-DSP
FPGA
IC1212
LVDS
DRIVE
A/D
41.344 MHz
A/D
MAIN UNIT
FPGA (IC1351)
LPF
90
LPF
Phase
shift
90
LO (DDS) Phase
shift
3-6
IC1331
D/A
IC1221
XTAL 124.032 MHz
AMP
BPF
D1251
PIN
A/D
ATT
Q1201
Q1202
IC1211
X1201
AMP BUFF
(41.344 MHz)
Mixer
D/A
LPF
Mixer
Image
Rejection
Mixer
L1281,L1282
C1281,C1283,C1285
LPF
D1232
RF
Transmit
RFsignal