NX-210(G)
13
3-3. Audio Amplifi er Circuit
Audio processing (high-pass filter, low-pass filter, de-
emphasized and so on) at FM mode and decoding at NXDN
mode are processed by DSP. The audio signal from IC309
and IC304 goes through the amplifier (IC802). The signal
then goes through a mute switch (IC805), amplifi er (IC809),
electronic volume control (IC801), and AF amplifi er (IC814).
While busy, AMT becomes Low to turn IC805 on, and the
signal is fed to the AF switch. While INAMT is High, the AF
switch (IC816) selects the internal speaker, and the audio
signal is fed to the internal audio power amplifi er (IC103),
and output to the internal speaker. While EXAMT is High, the
AF switch (IC816) selects the external speaker, and the au-
dio signal is fed to the external audio power amplifi er (IC817),
and output to the external speaker. The power supply for
IC103 and IC817 is turned on while INAMT or EXAMT is
High.
The speaker is switched by the logic of the speaker
switching terminal SSW on the universal connector. When
the SP-MIC is not attached, SSW becomes High. IC309
detects the logic of SSW and activates either INAMT or EX-
AMT.
Q810
Q806
IC816
IC103
VDD
INT. SP
SHUT DOWN
B
INAMT
EXAMT
AF signal
from IC814
IC817
VDD
EXT. SP
SHUT DOWN
Fig. 3 Audio amplifi er circuit
3-4. Squelch Circuit
It amplifies the demodulated noise signal from IC309
after fi ltering through the BPF circuit. Then, the amplifi ed sig-
nal is converted to a DC signal by the detection circuit. The
converted signal is fed back to IC309.
DET
IC309
IC811
(1/2)
ASQAPC
ASQDET
LPF
IC815
(2/2)
HPF
Q808
AMP
D807
RECT
IC815
(1/2)
AMP
Fig. 4 Squelch circuit
4. Transmitter System
4-1. Audio Band Circuit
The signal from the internal microphone goes through the
mute switch (Q812). When the SP-MIC is not attached, the
microphone switching terminal (MSW) on the universal con-
nector becomes High, and the mute switch (Q812) is turned
on. When the SP-MIC is attached, MSW is connected to
GND inside the SP-MIC. For this reason, Q812 is turned off,
the internal microphone is muted, and only the input of the
external microphone is supplied to the microphone ampli-
fi er. The signal from the microphone goes through the mute
switch (Q807), and is amplifi ed by IC813 (1/2) and limited
by the AGC circuit which is composed of D801, D802, Q803
and Q804.
4-2. Base Band Circuit
The audio signal output from the base band circuit is con-
verted to digital data with a sampling frequency of 48kHz.
This digital data is sent to the DSP (IC304), and voice sig-
nals of 300Hz or lower and frequencies of 3kHz or higher
are cut off and an audio range of 300Hz to 3kHz is extracted.
The audio signal is then pre-emphasized in FM mode and
synthesized with the signals, such as QT and DQT, as re-
quired, and is then output from IC309. In Digital mode, the
audio signal is converted to the 4-Level FSK base band sig-
nal and output from IC309. The DTMF and MSK base band
signals are also generated by the DSP and output by IC309.
The processed baseband signal is output from IC304 and
IC309. The signal from IC304 deviates the frequency of the
PLL IC (IC503). The signal from IC309 is fi ltered with the
LPF (IC803), and adjusts the level with DAC (IC801), and
deviates the frequency of the VCO..
SW
Q807
IC808
MM
AMP
IC807
(1/2)
LPF
IC804
LPF
IC803
(1/2)
AMP
IC801
IC807
(2/2)
IC309
ASIC
IC304
DSP
LPF
IC803
(2/2)
AMP
PLL
IC503
VCO
IC505
(1/2)
AMP
AGC
IC813
(1/2)
D801,D802
Q803,Q804
SW
Q812
Q811
SW
MSW
SCSW
INT. MIC
EXT. MIC
VC
TCXO
X501
Fig. 5 Audio band and Base band circuit
CIRCUIT DESCRIPTION
