Kenwood NX-5200 Service Manual page 17

2.4.5 PLL Frequency Synthesizer

2.4.5.1

TCXO (X700)

TCXO (X700) generates a reference frequency of 19.2MHz for the PLL frequency synthesizer. This reference signal is buffered by

Q700 and IC700. And it is distributed to TX PLL (IC100), RX PLL (IC200), IF IC (IC600), GPS/Bluetooth (IC850), and IC702.

The frequency adjustment is achieved by adjusting a D/A converter (IC901) output in the voltage of the control terminal of TCXO.

2.4.5.2

VCO

There are TX VCO and RX VCO.

The TX VCO (Q160) generates the carrier for the transmitter. The VCO oscillation frequency range is 136 to 174MHz. The transmit

frequency range is 136 to 174MHz.

The RX VCO (Q240) generates the 1st local signal for the receiver.

The VCO oscillation frequency range is 185.95 to 223.95MHz. The 1st local signal frequency range is 185.95 to 223.95MHz.

The VCO oscillation frequency is determined by voltage control terminals "CV" and "ASSIST". The voltage control terminal "CV" is

controlled by PLL IC (IC100 for TX PLL, IC200 for RX PLL). The voltage control terminal "ASSIST" is controlled by the control voltage

from D/A converter (IC901).

For the modulation input terminal, "VCO_MOD" of TX VCO (Q160), the output frequency changes according to the applied voltage.

This is used to modulate the VCO output.

2.4.5.3

PLL IC

There are TX PLL IC and RX PLL IC. PLL ICs compare the difference in phases of the VCO oscillation signal and the TCXO reference

frequency. And it returns the difference voltage to the VCO CV 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 MPU is used before control by the PLL IC to bring the VCO oscillation frequency

close to the desired frequency. As a result, the VCO CV voltage does not change and is always stable at approx. 2.0V.

The desired frequency is set for the PLL IC by the MPU (IC702) through the 3-line "SDO1", "SCK1", "/PCS_R" serial bus for RX PLL

and "SDO1", "SCK1", "/PCS_T" serial bus for TX PLL. The MPU monitors through the "PLD_R" and "PLD_T" signal line, whether the

PLL IC is locked or not. If the VCO does not lock to desired frequency (unlock), the "PLD_R" and "PLD_T" logic is low.

2.4.6 Control Circuit

The control circuit consists of MPU/DSP (IC702) and its peripheral circuits. IC702 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.

2.4.6.1

MPU

The MPU/DSP (IC702) is 32-bit RISC processor and fixed floating-point VLIW DSP, equipped with peripheral function.

This MPU operates at 288MHz (MAX) clock and 3.3V /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.

2.4.6.2

Memory Circuit

Memory circuit consists of the MPU (IC702) and the Mobile DDR (IC703), the flash memory (IC705). The flash memory has capacity

of 512M-bit that contains the transceiver control program for the MPU and stores the data. It also stores the data for transceiver chan-

nels and operating parameter that are written by the FPU. This program can be easily written from external devices. The Mobile DDR

has capacity of 512 M-bit. The MPU copies the program to the Mobile DDR from the flash memory. The MPU is used as a work area

Mobile DDR.

Flash Memory

Note:

The flash memory stores the data that is written by the FPU (KPG-D1/D1N), tuning data (Deviation, Squelch, etc.), and firmware

program (User mode, Test mode, Tuning mode, etc.). This data must be rewritten when replacing the flash memory.

Mobile DDR (static memory)

Note:

Mobile DDR is used as a work area of the MPU.

2.4.6.3

LCD

The LCD is controlled using parallel interface from the MPU (IC702).

2.4.6.4

Key Detection Circuit

Keys are detected using I/O Expander IC (IC708). If pressed key is detected by IC708, it is informed to the MPU (IC702) through serial

line.

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