Kenwood TK-7150 4. PLL Frequency Synthesizer, 5. Control Circuit

TK-7150

3-4. Automatic Power Control, Circuit and Transmitter

The automatic power control (APC) circuit stabilizes the

transmitter output power at a predetermined level, and con-

sists of forward/reflected power detector circuits. The for-

ward/reflected power detector circuits detects forward RF

power and reflected RF power to DC voltage, and consists of

a C coupling type detection circuit, RF detector D5/D6, and

DC amplifier IC2 (A/2).

The voltage comparator (IC2 B/2) compares the voltage

obtained by the above detected voltage with a reference volt-

age, set using the microprocessor and IC718 and IC715.

An APC voltage proportional to the difference between

the sensed voltage and the reference voltage appears at the

output of IC2. This output voltage controls the gate voltage

for the drive amplifier Q4 and final amplifier Q5, which keeps

the transmitter output power constant.

4. PLL Frequency Synthesizer

The transmit signal and the receive first L.O. signal are

generated by the PLL digital frequency synthesizer. The fre-

quency synthesizer consists of a transmitter voltage con-

trolled oscillator (TX VCO; Q507), a receiver voltage con-

trolled oscillator (RX VCO; Q509), a buffer amplifier (Q513

and Q515), an RF amplifier (Q516), a low-pass filter (Q501,

Q503 and Q504), a PLL IC (IC501), and TX VCO/RX VCO

switches (Q510 and Q512).

In the transmit signal mode, an operating frequency pro-

gramming data is sent to IC501, from the CPU (IC701), to set

the programmable counter within IC501. Q512 is turned on

to activate the TX VCO and the output signal of the TX VCO is

amplified by Q513 and Q516.

The signal is then divided down in frequency, at the pro-

grammable counter in IC501, to 5.0kHz or 6.25kHz, 7.5kHz

which is compared in phase with a 5.0kHz or 6.25kHz, 7.5kHz

reference signal, derived from 16.8MHz VCXO (X501) and a

Q507

BUFF

AMP

BUFF

AMP

TX VCO

SW Q512

SWSW Q510Q514

8CL 8CL 8C 8T

Q509

RX VCO

8CL

PLL IC

IC701

CPU

8CL

STR

Q516

VCXO 5C

X501

16.8MHz

Q513 Q515

LPF

12CL

Q501

Q503

Q504

D513

D514

IC501

SW SW

Q518 Q519

Fig. 4 PLL circuit

1/3360 or a 1/2688, 1/2240 fixed counter in IC501, at the

phase comparator in IC501. The VCXO operates at 16.8MHz

and its frequency stability is maintained within 2.5ppm (tem-

perature range of –30 to +60 degrees).

The phase comparator output signal is fed into a low-pass

filter (Q501, Q503 and Q504) before being applied tot the TX

vco as a frequency control voltage. This low-pass filter’s

power is supplied by the DC/DC converter (Q502, Q505,

Q506, Q508, and Q511). If an unlock condition occurs in the

phase locked loop, this condition is detected by Q518 and

Q519. This cause the transmitter 8V supply cut off, resulting

in the prevention of an unauthorized transmission.

The transmitter modulation signals (processed Mic. audio

and sub-audible signalling) are applied to the TX VCO for fre-

quency modulation.

In the receive mode, the VCO is substituted with Q509

(RX VCO) and it generates the receiver first local oscillator

signal according to the data sent from the CPU (IC701). The

basic operation of the synthesizer remains the same.

5. Control Circuit

The control circuit mainly consists of CPU, memory cir-

cuit, DSP circuit, and power supply circuit.

5-1. CPU

The CPU (IC701) controls the flash ROM (IC705), the DSP

(IC710), the receiver circuit, the transmitter circuit, the con-

trol circuit, and the display circuit and transfers data to or

from an external device.

5-2. Memory Circuit

IC705 has a flash ROM with a capacity of 4M bits that

contains the control program for the CPU, the signal process-

ing program for DSP and data such as channels and operating

features.

This program can be easily written from an external de-

vices. Data such as the operating status are programmed

into the EEPROM (IC704).

IC700/702

EEPROM

Reset IC

Shift register IC

IC718

D/A IC

IC703

232C driver

IC705IC704

IC103

Flash ROM

Interface IC

IC701

CPU

IC706~709

DSP IC710

CODEC IC IC713

INV

IC711

X700

12.288MHz

Q700

BEAT

SHIFT

Fig. 5 Control circuit

CIRCUIT DESCRIPTION