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IMPROVED OUTPUT RESPONSE TliVlE IN CONTROL LOOPS USING AN INTEGRATOR

IP.com Disclosure Number: IPCOM000008985D
Original Publication Date: 1999-Jan-01
Included in the Prior Art Database: 2002-Jul-29
Document File: 5 page(s) / 207K

Publishing Venue

Motorola

Related People

Gadi Shirazi: AUTHOR [+3]

Abstract

This paper deals with the implementation of the LDMOS PA (Power Amplifier) module and the power control loop associated with it in VHF/UHF HAMMER portable radios, and modifications that have been made to meet the ETSI requirements. One of the requirements was to change the radio's circuits so that they will accommodate and meet the ETSI requirements.

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CR MO7VROLA

Technical Developments

IMPROVED OUTPUT RESPONSE TliVlE IN CONTROL LOOPS USING AN INTEGRATOR

by Gadi Shirazi, Ely Basry and Erez Bar-on

INTRODUCTION

  This paper deals with the implementation of the LDMOS PA (Power Amplifier) module and the power control loop associated with it in VHF/UHF HAMMER portable radios, and modifications that have been made to meet the ETSI requirements. One of the requirements was to change the radio's circuits so that they will accommodate and meet the ETSI requirements.

The requirements that the radio had to meet were:

1. The power should reach its final desired level in a maximum time of 2Oms.

2. The power should increase uniformly from -3OdBc to -6dBc within a minimum time of 0.2ms.

3. The power should increase to 0 within a maximum time of 25ms.

4. The power should decrease uniformly from - 6dBc to -3OdBc within a minimum time of 0.2ms.

5. During transients, an adjacent channel should not be interfered with.

PROBLEMS TO BE SOLVED

In the following, TX refers to transmission mode and RX refers to reception mode.

  1) A BIPOLAR PA module could not meet the ETSI requirements due, to the finite RF isolation between in and out (i.e. there is some RF leakage between in and out). Therefore, at the transition moment between TX and RX, the VCO (voltage controlled oscillator) is affected so that its frequency may be modified due to ,the first stage's impedance change (at rise and fall time). Also because of the finite isolation between the input and the output of the PA, the RF signal may leak from the VCO to the output and its frequency change may cause interfer- ence into the adjacent channel. (One of the ETSI requirements is to ensure that during transition between TX and RX and vice versa, the adjacent channel experience interference).

  2) The loop should control the output power at two levels: 1W and 4W. According to ETSI, the power must reach its final level within 20ms. Unfortunately, at lW, the time elapsed between TX turn-on until the moment in which the power begins to rise is too long to meet the ETSI requirement. Because the loop control should cater for two power levels using the same hardware, it was necessary to expedite the rise time by software.

PROPOSED SOLUTION TO THE PROBLEMS

  Because BIPOLAR technology is not suitable, we have used an LDMOS PA module. This technol- ogy has the advantage that its RF isolation between in and out is much better than that of BIPOLAR (at Vcontrol=OV), so any interference at the VCO'S fre- quency caused by impedance change at the PA input stage will not appear at the output.

0 Motorota. Inc. ,999 122 January I999

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MOTOROLA Technical Developments

  The LDMOS technology also has the advantage that it is more stable and more efficient than BIPO- LAR.

  Referring to Figure 1 (and the PA control loop block diagram), the PA control loop is based on DC current control. Because the output power i...