GB2387507A

GB2387507A - Mobile radio communications device with two oscillators for providing two clocks

Info

Publication number: GB2387507A
Application number: GB0208486A
Authority: GB
Inventors: Richard Ormson
Original assignee: NEC Technologies UK Ltd
Current assignee: NEC Technologies UK Ltd
Priority date: 2002-04-12
Filing date: 2002-04-12
Publication date: 2003-10-15
Anticipated expiration: 2022-04-12
Also published as: GB0208486D0; GB2387507B

Abstract

A mobile radio communication device having a first crystal oscillator for providing a first master clock frequency for a timebase of a first communication system to which the device is connected, and a second crystal oscillator for providing a second clock frequency for a timebase for a second communication system to which connection may be required, respective first and second digital/analogue converting means for delivering control signals to each of the first and second oscillators for producing the said first and second clock signals, and including means for determining the digital value of the second digital/analogue convertor on the basis of a digital value of the first digital/analogue convertor and first and second offset values associated with the circuitry of the first and second communication systems respectively.

Description

MOBILE RADIO COMMUNICATIONS DEVICE

AND METHOD OF OPERATION

The present invention relates to a mobile communications 5 device, and related method of operation and, in particular, to a mobile phone and related method of operation.

Mobile phones comprise a master clock circuit for generating a relatively high frequency clock signal which forms part of the 10 timebase circuitry within the mobile phone. The timebase generated within the mobile phone is intended to be synchronized with a timebase of a base station with which the mobile phone is communicates in accordance with a particular communication system such as, for example, the Global System 15 for Mobile Communication (GSM). Such synchronization is usually achieved by use of an automatic frequency control (AFC) mechanism which operates by comparing the frequency of certain signals received from the base station with the frequency of the local clock and then adjusting the local 20 clock to remove the observed frequency difference.

A plurality of mobile communication systems available have been developed which require different master clocks and timebases for their operation.

A mobile phone offering access to two or more such systems would therefore be advantageous since the same mobile phone handset could then be used with a selected one of the different communication systems supported. This choice of 30 system for the same mobile phone would therefore lead to a greater geographical coverage for one and the same mobile phone since the different communication systems commonly exhibit geographical boundaries. This geographical limit commonly occurs at international boundaries and also occurs as 35 a consequence of the time taken to achieve full coverage of a new network technology. Such a dual mode mobile phone would therefore be particularly attractive to users who travel overseas and also to the early users of new technology

communication systems.

In order to achieve such interoperability between two respective communications systems, a mobile phone will require 5 at least two master clock circuits serving to track the timebases and air interfaces of the respective communication systems. In order to be practically viable, such multi-mode interoperability should allow for ease of handover from one communication system to the other.

iO In, for example, a dual-mode handset, there will be independent frequency control loops for each of the respective communication systems and potential problems will arise with regard to maintaining of the clock accuracy of the slave 15 system, i.e. the circuitry associated with a communication system to which the mobile phone is not currently communicating, while the mobile phone is communicating with its current master system.

20 In order to achieve a smooth and effective handover from one communication system to the other, the clock of the slave system should be within a defined frequency range.

However, since, at attempted handover, there will have been 25 insufficient signal receptions from the slave communication system associated with the slave circuitry, the signal tracking loop of the slave circuitry will not have reached the required accuracy to actually achieve hangover. Also at the time of handover, the tracking system of the master circuitry 30 associated with the communication system to which the mobile phone is currently connected, is likely to have control of the master clock signals generated in the mobile phone and associated with both communication systems such that any data gathered by the tracking system associated with the slave 35 communication system may potentially be subjected a unknown and varying offset imposed by the master system.

It is therefore appreciated in terms of the present invention

that the data then gathered by the slave tracking system associated with the slave communication system may be invalid.

The present invention seeks to provide for a mobile radio 5 communication device, and related method of operation, which can allow for a smooth and efficient hangover within a mobile phone from operation with a first communication system to operation with a second communication system.

10 According to a first aspect of the present invention there is provided a mobile radio communication device having a first crystal oscillator for providing a first clock frequency for a timebase of a first communication system to which the device is connected, and a second crystal oscillator for providing a 15 second clock frequency for a timebase for a second communication system to which connection may be required respective first and second digital/analogue converting means for delivering control signals to each of the first and second oscillators for producing the said first and second clock 20 signals, and including means for determining the digital value of the second digital/analogue convertor on the basis of a digital value of the first digital/analogue convertor and first and second offset values associated with the circuitry of the first and second systems respectively.

In accordance with the present invention, the automatic frequency control of the second system is thereby effectively seeded by the first system. Such seeding of the automatic frequency control of the second system advantageously serves 30 to achieve the same voltage controlled oscillator offset, expressed in parts per million (ppm) at communication system handover as existed prior to handover.

Preferably therefore, the first and second crystal oscillators 35 can be operatively connected by means of a phase locked loop which serves to lock the two oscillators together.

Such an arrangement is disclosed in the applicant's co-pending

Application No. **(agent's reference P700348GB) having the same filing date as the present application.

With such an architecture, the present invention can be s achieved in an advantageously simple manner by ensuring that the voltage from the digital/analogue convertor of the second system is the same as that from the digital/analogue convertor of the first system. Then, at handover between the communication systems, the control voltage delivered to the 10 locked first and second oscillators will not then change and, likewise, neither will the frequency of operation.

Preferably, the output voltage is maintained constant through determination of the digital value of the second system and 15 the constant and offset values for the digital/analogue convertor of the second system. Such constant and offset values can advantageously be determined by way of the standard linear digital analogue convertor equation 20 Output voltage = (digital value x constant) + offset.

The constant and offset values are in any case commonly listed as part of the device data sheet or can be determined through simple experimentation.

Advantageously, having identified the two variables for each digital analogue convertor, consistency between the two voltage outputs can be achieved through the representation: in which the first system is referred to as the master system and 30 the second system is referred to as the slave system.

digital value (master) x constant (master) + offset (master) = digital value (slave) x constant (slave) + offset (slave) 3s From this relationship, it will be readily appreciated =hat in order to arrive at a setting on the digital/analogue convertor of the slave system, the following relationship can then be employed:

s digital value (slave) = (digital value (master) x constant (master) + offset (master) - offset (slave)) constant (slave) In accordance with another embodiment, in which separate independent oscillators are employed, the present invention can serve to ensure that the same ppm offset applies to both clock signals derived from the respective oscillators.

1() Advantageously, such consistency is achieved by way of the relationship of the ppm offset to the digital value of the system and the related constant and offset values associated with the crystals.

Such a relationship is defined by: ppm offset = (digital value x constant) + offset 20 Preferably, the constant and offset values are obtained through calibration of the crystal. Once calibrated however, and in order to ensure common ppm offset between both clock signals, the digital value associated with the slave system can again be identified from the digital value of the master 25 system, the offset of the master system, the offset of the slave system and the constant value of the slave system.

Thus, when seeking handover from a known setting on the digital/analogue convertor of the master system to the unknown 30 required setting of the digital/analogue convertor of the slave system, such unknown setting can be identified from the relationship: digital value (slave) = (digital value (master) x constant 35 (master) + offset (master) - offset (slave)) constant (slave). In this manner, from known, or readily identifiable constants

and variables associated with the circuitry within a mobile phone from the two respective communication systems, the appropriate control setting for the digital/analogue convertor of the slave system can be achieved in order to ensure that, s at hangover, the clock of the slave system is within the required frequency range.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings in 10 which: Fig. 1 is a schematic block diagram of a mobile radio communication device embodying one aspect of the present invention; and Fig. 2 is a schematic block diagram of a mobile radio communication device embodying another aspect of the present invention. 20 Turning first to Fig. 1 there is illustrated, in block schematic form, circuitry 10 within a mobile phone handset which is arranged to provide dual-mode interoperability insofar as the handset can be switched between use with the Universal Mobile Telecommunication system (UMTS) or the Global 25 System for Mobile Communication (GSM).

In this manner, the mobile phone handset comprises respectively mirrored circuits for driving the respective oscillators providing for local timebases associated with each 30 communication system. Circuitry 12 associated with the UMTS side of the mobile phone comprises an automatic frequency control 16 arranged to feed an output signal to a digital/analogue convertor 18 which in turn provides an output signal to a switch 20. The GSM side of the handset comprises 35 circuitry 14 which likewise includes an automatic frequency control 22, and a digitalianalogue convertor 24 which, as with the digital analogue convertor 18 of the UMTS side of the mobile phone, delivers its output to the switch 20.

By means of the switch 20, either one of the outputs of the digital/analogue convertor 18 or the digital/analogue convertor 24 is delivered to the series connected oscillators 26, 28 which are looked together by way of a phase locked loop 5 (not shown).

Such manner of control and connection between the respective oscillators of such a dual-mode mobile phone is the subject of the applicant's copending Application No. **** (client's to reference: P700348GB) having the same filing date as the present invention. The oscillator 26 is arranged for developing a 19.2MHz clock signal for forming the local time base of the mobile phone when communicating with a UMTS base station, whereas the oscillator 28 is arranged to develop a 15 13MHz clock signal for defining the local timebase of the mobile phone when communicating with a GSM base station.

With such an architecture, it is merely required to ensure that the voltage from one digital/analogue convertor is the 20 same as the other. Thus, at handover, the control voltage does not change, and so neither does the frequency. Linear digital/analogue convertors, as generally used for controlling voltage controlled oscillators comply with the equation: 95 Voltage output = (digital value x constant) + offset Thus, to translate between two digital/analogue convertors "constant" and "offset" for each of the digital/analogue convertors is determined. This information is generally So listed in the converters data sheet, although it can be simply determined experimentally.

Having determined the two variables for each digital/analogue convertor, the output voltages will be the same if, for two 35 communication systems A and B: digital value (A) x constant (A) + offset (A) = digital value (B) x constant (B) + offset (B)

Thus, in order to achieve a setting on digital/analogue convertor (B) from a known setting digital/analogue convertor (A): s digital value (B) = (digital value (A) x constant (A) + offset (A) - offset (B))/constant (B).

Likewise, if a handover from system B to system A is required 10 then the following relationship is employed: digital value (A) = (digital value (B) x constant (B) + offset (B) - offset (A))/constant (A).

15 Such control and computation can be achieved by way of a handover conversion function element 26.

Turning now to Fig. 2, there is shown an alternative embodiment of the present invention in which the respective 20 oscillators associated with the two communication systems are arranged for independent operation.

Circuit elements corresponding to those illustrated in Fig. l include the same reference numerals but, as will be 25 appreciated, each respective digital/analogue convertor 18, 24 feeds into each respective oscillator 26, 28 in an independent manner. In this embodiment, a control conversion function element 30 30 is illustrated which is arranged to conduct the calculations required so as to arrive the required setting for the digital/analogue convertor associated with the slave communication system.

35 For this embodiment, it becomes important to ensure the same ppm offset applies to both clocks. This is achieved in a similar way to the previous embodiment comprising for locked clocks, as the equation for ppm offset is

ppm offset = (digital value x constant) + offset.

However, the value of offset varies between individual crystals and so calibration of each handset is required to establish these constant and offset values. However, this only needs to be performed once, for example as part of a factory calibration procedure) and then the same needs to be performed once (as part of a factory calibration procedure, 10 and then the same equations as above can be used.

Thus to hangover from system A to system B. i.e. to go from a known setting on digital/analogue convertor (A) to a setting on digital/analogue convertor(B): digital value (B) =(digital value (A) x constant (A) + offset (B))/ constant (B)) A handover from system B to system A, the following 20 relationship can therefore be used: digital value (A) = (digital value (B) x constant (B) + offset (B) - offset (A)) /constant (A) 25 Thus, in summary, it will be appreciated from Fig. 1 that the

handset architecture can incorporate two crystal oscillators locked together by a phone locked loop. There are two points of origin for the Automatic Frequency Control (AFC) signals to the system clocks. One control originates in the GSM side 14 30 of the handset, the other in the UMTS side 12. It should be noted it is intended that the software driving these two AFC signals operate independently. The exception to this is at system handover, where the AFC for the new system is to be seeded with the current AFC setting of the old system.

Only the AFC line for the current i.e. master system will be connected to the crystal. This is achieved in hardware by way of the switch 20. The control for the switch 20 can be

lo provided from either a Digital Signal Processor or the CPU (not shown). If a DSP is chosen, it is arranged such that a low signal to the switch causes the other system's AFC to be connected. If this control configuration is not provided, the s slave system will need to be active simply to ensure that the correct signal is connected and this unnecessarily increases power consumption.

Similar considerations arise within the embodiment of Fig. 2.

2s

Claims

1. A mobile radio communication device having a first crystal oscillator for providing a first master clock 5 frequency for a timebase of a first communication system to which the device is connected, and a second crystal oscillator for providing a second clock frequency for a timebase for a second communication system to which connection may be required, respective first and second digital/analogue 10 converting means for delivering control signals to each of the first and second oscillators for producing the said first and second clock signals, and including means for determining the digital value of the second digital/analogue convertor on the basis of a digital value of the first digital/analogue 15 convertor and first and second offset values associated with the circuitry of the first and second communication systems respectively.

2. A device as claimed in Claim 1, wherein the said means 20 for determining the digital value of the second digital/analogue convertor is arranged to operate on the basis of a common oscillator offset before and after system handover. 25

3. A device as claimed in Claim 2, and arranged to maintain a common oscillator offset on the basis of the relationship of the offset to the digital value of the systems and related constant and offset values of the crystal oscillators.

30

4. A device as claimed in Claim 1, wherein the said first and second oscillators are operatively locked together by means of a phase locked loop.

5. A device as claimed in Claim 4, wherein the said means 5 for determining the digital value of the second digital/analogue convertor is arranged to operate on the basis of a common output voltage from the respective digital/analogue convertors of the two systems.

6. A device as claimed in Claim 5, and arranged to maintain a common output voltage from the digital/analogue convertor during system handover.

5

7. A method of operating a mobile radio communication device having a first crystal oscillator for providing a first clock frequency for a timebase of a first communication system to which the device is connected, and a second crystal oscillator for providing a second clock frequency to a timebase for a 10 second communication system to which connection may be required, and including respective first and second digital/analogue converting means, for delivering control signals to each of the first and second oscillators for producing the said first and second clock signals, and IS including the step of determining the digital value of the second digital/analogue convertor on the basis of a digital value of the first digital/analogue convertor and first and second offset values associated with the circuitry of the first and second communication systems respectively.

8. A method as claimed in Claim 7, wherein the said step of determining the digital value is conducted on the basis of maintaining a common oscillator offset before and after hangover between the two systems.

9. A method as claimed in Claim 8, wherein the said step of determining the digital value is conducted on the basis of the relationship of the offset to the digital value of the systems and the related constant and offset values of the crystal 30 oscillators.

10. A method as claimed in Claim 7, wherein the step of determining the said digital value is conducted on the basis of a common output voltage from the respective 35 digital/analogue convertors of the two systems during system hangover and with regard to the digital value of the second system and the constant and offset values of the digital/analogue convertor of the second system.

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11. A mobile radio communication device having a first crystal oscillator for providing a first clock frequency for a timebase of a first communication system to which the device 5 is connected, and a second crystal oscillator for providing a second clock frequency for a timebase for a second communication system to which connection maybe required, and substantially as described herein with reference to, and as illustrated in Fig. 1 and Fig. 2 of the accompanying drawings.

12. A method of controlling a mobile radio communication device having a first crystal oscillator for providing a first clock frequency for a timebase of a first communication system to which the device is connected and a second crystal 15 oscillator for providing a second clock frequency for a timebase for a second communication system to which connection maybe required, and substantially as hereinbefore described with reference, and as illustrated, in Fig. 1 and Fig. 2 of the accompanying drawings.

:i \(om39Eo^E I Application No: GB 0208486.1 I YE Examiner: Emma Rendle Claims searched: 1-12 Date of search: 7 October 2002 Patents Act 1977 Search Report under Section 17 Databases searched: UK Patent Office collections, including GB, EP, WO & US patent specifications, in:

UK C1 (Ed.T): H4L (LEP, LRPTC, LDSS) Int Cl (Ed.7): H04B 1/40,7/26; H04L 7/033; H04Q 7/32 Other: Online: WPI, EPODOC, PAJ Documents considered to be relevant: Category Identity of document and relevant passage Relevant to claims X US 6 125 268 ( ERICSSON) see whole document. I and 7 at least X US 5 793 227 (IBM) see whole document, especially claim 1 and I and 7 at figures. least X Document indicating lack of novelty or inventive step A Document indicating technological background and/or state of the art.

Y Document indicating lack of inventive step if combined P Documentpublishedonorafterthedeclaredprioritydatebutbeforethe with one or more other documents of same category. filing date of this invention.

E Patent document published on or after, but with priority date earlier & Member of the same patent family than, the filing date of this application.

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