Motorola MagOne Manuel - Page 21

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Transmitter System and PLL Synthesizer

3.0

Transmitter System and PLL Synthesizer

LPF

The transmitter consists of: Microphone, Pre-emphasis, Modulator, Drivers, Power Amplifier, Low-

Pass Filter, Antenna Switch and an Auto-Power Control.

3.1

TX Power Stage

The TX VCO output signal is channeled by the TX power stage via an attenuator. The attenuator is

pie style resister attenuator, and is used for isolation between the VCO and power amplifiers.

The TX Power stage is consist of: pre-drive (Q401), drive amplifier (Q402) and final amplifier

(Q403). The -4dBm TX RF signal from the attenuator is increased to around +25dBm by the pre-

drive and the drive amplifier.

The TX signal from drive amplifier is next amplified by final amplifier (Q403). It passes through a

strip line for impedance matching, and a low pass filter to suppress unwanted harmonics via the

antenna switch.

3.2

Antenna Switch

The antenna switch is for enabling the TX section and the RX section to share the antenna.

In transmit mode, PIN diodes (CR401, CR301, CR302) are forward biased and these enable the RF

signal to pass to the antenna.

3.3

Low Pass Filter

The TX Low Pass Filter consist of a fifth Chebyshev filter and reduces the unwanted spurious for TX

output power from final Amplifier : C426~430, L409, L410.

FINAL

AMP

CR401

Q403

ANT-SW

R417

BATT.

CURRENT

DETECT

DRIVE

P.DRIVE

AMP

Q402

Q401

U401

APC

PLL DATA

VCTCXO

3DB

ATTEN

VCO

LOOP

FIL.

PLL

U701

2-3

REG. 5.8V

U106

AUDIO

(From filter)