Kenwood NX-3400 Service Manual page 14

2.3.5.2 VCO
There are two VCO contain VCO_L for 800MHz and VCO_H for 900MHz.
The VCO_H (Q131) generates the carrier for the transmitter (Frequency range: 896 to 941MHz) and the receiver (Frequency range:
935 to 941MHz). VCO oscillation frequency range is 1792 to 1882MHz.
The VCO_L (Q151) generates the carrier for the transmitter (Frequency range: 806 to 870MHz) and the receiver (Frequency range:
851 to 870MHz). VCO oscillation frequency range is 1612 to 1740MHz.
The both VCO (VCO_H and VCO_L) oscillation frequency is divided as 1/2 by Transceiver IC (IC303) and it becomes the carrier for
the Transmitter and the Receiver (Direct conversion).
The VCO oscillation frequency is determined by voltage control terminals "CP" and "ASSIST".
The voltage control terminal "CP" is controlled by PLL (incorporated in Transceiver IC (IC303)). The voltage control terminal "ASSIST"
is controlled by the control voltage from D/A converter (IC410).
For the modulation input terminal, "VCO_MOD3" of PLL (incorporated in Transceiver IC (IC303)), the output frequency changes
according to the applied voltage. This is used to modulate the VCO output.
2.3.5.3 PLL
PLL (incorporated in Transceiver IC (IC303)) compares the difference in phases of the VCO oscillation signal and the TCXO (X401)
reference frequency. And it returns the difference voltage to the VCO CP terminal and realizes the "Phase Locked Loop". This allows
the VCO oscillation frequency to accurately match (lock) the desired frequency.
When the frequency is controlled by the PLL, the frequency convergence time increases as the frequency difference increases when
the set frequency is changed. To supplement this, The ASSIST Voltage from D/A converter (IC410) is used before control by the PLL
(incorporated in Transceiver IC (IC303)) to bring the VCO oscillation frequency close to the desired frequency. As a result, the VCO
CP voltage does not change and is always stable at approx. 2.5V.
The desired frequency is set for the PLL (incorporated in Transceiver IC (IC303)) by the MPU/DSP (IC401) through the 3-line "/
DCR_CS", "DCR_DO", "BCLK" serial bus for PLL. MPU/DSP (IC401) monitors through the "PLD", whether the PLL (incorporated in
Transceiver IC (IC303)) is locked or not. If the VCO does not lock to desired frequency (unlock), the "PLD" logic is low.
2.3.6 Control Circuit
The control circuit consists of MPU/DSP (IC401) and its peripheral circuits. MPU/DSP (IC401) mainly performs the following;
(1) Switching between transmission and reception by PTT signal input.
(2) Reading system, zone, frequency, and program data from the memory circuit.
(3) Sending frequency program data to the PLL.
(4) Controlling the audio mute circuit by decode data input.
2.3.6.1 MPU
The MPU/DSP (IC401) is 32bit RISC processor and Fixed/Floating-Point VLIW DSP, equipped with peripheral function.
This MPU/DSP (IC401) operates at 288MHz (MAX) clock and 3.2V/1.8V/1.2V DC. Controls the flash memory, Mobile DDR, the receive
circuit, the transmitter circuit, the control circuit, and the display circuit and transfers data to or from an external device.
2.3.6.2 Memory Circuit
Memory circuit consists of the MPU/DSP (IC401) and the Mobile DDR (IC402), the flash memory (IC404).
The flash memory has capacity of 512Mbit that contains the transceiver control program for the MPU/DSP (IC401) and stores the data.
It also stores the data for transceiver channels and operating parameter that are written by the FPU. This program can be easily written
from external devices. The Mobile DDR has capacity of 512Mbit. The MPU/DSP (IC401) copies the program to the Mobile DDR from
Flash memory.
Flash memory
Note:
The flash memory stores the data that is written by the FPU (KPG-D3/D3N), tuning data (Deviation, Squelch, etc.), and firmware
program (User mode, Test mode, Tuning mode, etc.).
Mobile DDR
Note:
Mobile DDR is used as a work area of the MPU/DSP (IC401).
2.3.6.3 LCD
The LCD is controlled using parallel interface from the MPU/DSP (IC401).
2.3.6.4 Button Detection Circuit
Buttons are detected using the MPU/DSP (IC401).
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