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Crystal Oscillator Level Detection for Improved Security on PLL Based Transmitter

IP.com Disclosure Number: IPCOM000166827D
Publication Date: 2008-Jan-24
Document File: 3 page(s) / 63K

Publishing Venue

The IP.com Prior Art Database

Abstract

This article describes a solution to overcome a PLL (Phase Locked Loop) failure caused by crystal oscillator malfunction. In transmitter, this could lead to out of band transmission or transmission stop. The solution presented provides the information of that failure and some means to correct it.

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                                                                                                                Last update: January 24, 2008

Crystal

Oscillator Level Detection

for Improved Security

on PLL Based Transmitter

1          ABSTRACT

This article describes a solution to overcome a PLL (Phase Locked Loop) failure caused by crystal oscillator malfunction. In transmitter, this could lead to out of band transmission or transmission stop. The solution presented provides the information of that failure and some means to correct it.

2          INTRODUCTION

Integrated PLL based transmitters are used for short range transmission. The PLL generates an RF signal with a frequency defined by a reference crystal oscillator. The crystal oscillator, using an external crystal can fail in some conditions (temperature, aging, EMC). Failing may lead to the absence of oscillation.

Consequently, PLL may stop transmission or unlock to an out of band frequency. The RF Regulations forbid out of band transmission. In multi-channel applications, out of channel transmission may interfere with other transmission. It is then necessary to stop transmission when PLL behavior is not controlled. Thus, Power Amplifier is most of the time activated only when PLL is locked.

Present solution is a proposal to overcome that problem by providing the information of the crystal failure to stop RF transmission and take any available action to re-start crystal oscillation or change condition of oscillation.

This requirement is mandatory for some applications. RF transmitter used for TPMS (Tire Pressure Monitoring System) and RKE (Remote Keyless Entry) applications should have increased reliability and performances compared to available designs.

Crystal

failure is one concern in TPMS applications.

3          PREVIOUS ART

A lock detector is used to detect PLL unlock. Should PLL unlock for any reason, the lock detector will disable the power amplifier and stop transmission.

Depending on phase comparator choice and lock detector implementation, there may be a wrong lock detector behavior in case of crystal oscillator failure. Thus, it may be possible that PLL unlock and transmission may not be stopp...