(No.RA077<Rev.001>)1-9
2.3.4 Transmitter System
2.3.4.1
Audio Band Circuit
The signal from microphone is amplified through a microphone amplifier IC602 (including AGC function) and input into MPU/DSP
(IC501) for audio processing. Voice signals of 300Hz or lower and frequencies of 3kHz or higher are cut off and an audio range 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 required, and is transferred to PLL (IC2). The DTMF and MSK baseband signals are also generated by IC501.
In Digital mode, the audio signal is converted to the 4-Level FSK baseband signal and is transferred to VCO circuit.
2.3.4.2
Drive and Final amplifier
The signal from the Transceiver IC (IC200) is amplified by pre-drive amplifier (Q104). The output of the pre-drive amplifier is amplified
by the drive amplifier (Q106) and final amplifier (Q107) to 5W (4W when the power is medium and 1W when the power is low). Q106
and Q107 are MOS FET. The output of the final amplifier is then passed through the harmonic filter (LPF) and antenna switch (D101
and D102) and applied to the antenna terminal.
Fig.4 Transmitter System
2.3.5 PLL Frequency Synthesizer
2.3.5.1
TCXO (X1)
TCXO (X1) generates a reference frequency of 16.8MHz for the PLL frequency synthesizer.
The oscillation frequency is adjusted TCXO directly by controlled the D/A converter (IC604).
2.3.5.2
VCO
•
NX-1200 series
There is one VCO contain TX VCO and RX VCO.
The VCO (Q4) generates the carrier for the transmitter and the receiver. The VCO oscillation frequency range is 272 to 348MHz.
The transmit frequency range is same as receiver frequency range.
The local signal frequency range is also 272 to 348MHz.
The oscillation frequency is divided into two by IC200 and it becomes the operating frequency.
The VCO oscillation frequency is determined by voltage control terminals "CP" and "ASSIST".
The voltage control terminal "CP" is controlled by PLL (IC2). The voltage control terminal "ASSIST" is controlled by the control
voltage from D/A converter (IC604).
For the modulation input terminal, "MOD", the output frequency changes according to the applied voltage. This is used to modulate
the VCO output.
•
NX-1300 series
There is one VCO contain TX VCO and RX VCO.
The VCO (Q4) generates the carrier for the transmitter and the receiver. The VCO oscillation frequency range is 800 to 940MHz.
The transmit frequency range is same as receiver frequency range.
The local signal frequency range is also 800 to 940MHz.
The oscillation frequency is divided into two by IC200 and it becomes the operating frequency.
The VCO oscillation frequency is determined by voltage control terminals "CP" and "ASSIST".
The voltage control terminal "CP" is controlled by PLL (IC2). The voltage control terminal "ASSIST" is controlled by the control
voltage from D/A converter (IC604).
For the modulation input terminal, "MOD", the output frequency changes according to the applied voltage. This is used to modulate
the VCO output.
ANT SW
FINAL AMP
DRIVE AMP
TRANSCEIVER IC
VCO
PLL
TCXO
MPU/DSP
MIC AMP
MIC
IC501
IC602
D101
D102
IC200
Q106
Q107
PRE DRIVE
AMP
Q104
IC2
X1
16.8MHz
Q4
ANT
