Browse Prior Art Database

Method to prevent Interference during Phase Training in Cartesian Feedback Systems

IP.com Disclosure Number: IPCOM000010260D
Original Publication Date: 2002-Nov-13
Included in the Prior Art Database: 2002-Nov-13
Document File: 3 page(s) / 44K

Publishing Venue

Motorola

Related People

Klaus Dirksmeier: AUTHOR [+3]

Abstract

Transmitters using a Cartesian Feedback System require phase training for stable operation. To prevent disturbance by signals coming from the antenna and to avoid transmitting RF power during phase training, the transmitter output is fed to a 50-ohm load during phase training.

This text was extracted from a Microsoft Word document.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 50% of the total text.

Method to prevent Interference during Phase Training in Cartesian Feedback Systems

By Klaus Dirksmeier, Cizhong Xu, Bernhard Hammes

Abstract

Transmitters using a Cartesian Feedback System require phase training for stable operation. To prevent disturbance by signals coming from the antenna and to avoid transmitting RF power during phase training, the transmitter output is fed to a 50-ohm load during phase training.

Introduction

This paper describes how to prevent disturbance and emissions during phase training of transmitters using Cartesian Feedback Systems.

Problems To Be Solved

TETRA radios often use a Cartesian Feedback System (CFS) to increase the linearity of the RF power amplifier (PA) and in turn the RF power transmitted in the adjacent channels (ACP). In a CFS, see Figure 1, a part of the transmitted output power is fed back and summed to the input signal. For stable operation of this loop, the phase shift in the loop must remain within certain limits. To remain within these limits over a wide frequency range, a wide range of environmental conditions and component aging, the CFS requires a phase training. During this training, the best phase condition for a stable loop is determined and then set during the next transmission. The phase training is performed whenever the transmit frequency has changed, or when for some time no phase training has been done.

To perform the phase training, the radio transmits a normal signal. Then the phase of the feedback signal is changed until the feedback signal equals the forward input signal with a phase shift of 180 degrees. The determined phase shift is then used during the following transmit mode.

Problem:

The training result can be affected by any RF signal, which comes from the antenna connector and flows towards the RF power amplifier. This reverse signal adds to the coupled part of the forward power and, when high enough, can lead to a different phase shift during training. Reverse signals can result from antenna mismat...