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Low Band, 800 MHz, PassPort & 900 MHz Theory of Operation: Introduction 7-1

Chapter 7 Low Band, 800 MHz, PassPort & 900 MHz

Theory of Operation

7.1 Introduction

This chapter provides a detailed theory of operation for the radio components. Schematic diagrams

for the circuits described in the following paragraphs are located in Figures 9-238 through 9-284.

7.2 Low Band Transmitter

The low band transmitter consists of the following basic circuits as shown in Figure 7-1.

• Power amplifier (PA).

• Antenna switch/harmonic filter.

• Antenna matching network.

• Power control integrated circuit (PCIC).

Figure 7-1. Low Band Transmitter Block Diagram

7.2.1 Power Amplifier (PA)

The PA consists of two LDMOS devices:

• PA driver, U101.

• PA final stage, Q100.

The LDMOS driver (U101) provides 2-stage amplification using a supply voltage of 7.3V. The

amplifier is capable of supplying an output power of 0.3 W (pins 6 and 7) with an input signal of 2mW

at (pin16). The current drain is typically 120 mA while operating in the frequency range of

29.7–50 MHz. The power output of this stage is varied by the power control loop which controls the

voltage on pin 1.

PCIC

Driver

Antenna Switch

Harmonic Filter

PA Final

Stage

Vcontrol

SPI Bus

Gate Bias

Antenna Switch Bias

Antenna

Matching

Network

rom VCO

Power Amplifier (PA)

Motorola HT Series User Manual

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