1. Field of the Invention
The present invention relates to a switchable up-conversion loop device for a transmitting stage of a mobile phone.
2. Prior Art
Although applicable to any digital mobile phone system, the present invention and its underlined problems will be discussed with particular reference to a GSM mobile phone system.
The Global System for Mobile Telecommunication GSM is designed as an international digital cellular service. Originally, the 900-Megahertz band was reserved for GSM services. Since GSM first entered commercial service in 1992, it has been adapted to work at 1800 MHz for the Personal Communication Networks PCN in Europe, and at 1900 MHz for Personal Communications Services PCS in the United States. Accordingly, there are three main GSM-standards, i.e. GSM 900, GSM 1800 (PCN), and GSM 1900 (PCS). Each GSM standard specifies different frequency bands for the uplink frequency band, i.e. the communication from the mobile phone to the base station, and the downlink frequency band, i.e. the frequency band reserved for communication from the base station to the mobile stations. The uplink frequency bands or transmit frequency bands of GSM 900, GSM 1800 and GSM 1900 are respectively 890 to 915 MHz, 1710 to 1785 MHz and 1850 to 1910 MHz.
In view of the increasing mobility of people, especially of business men doing trade in different countries and continents, a mobile phone adapted to the GSM 900 standard cannot be used within a region where the GSM 1900 standard is employed. If, for instance, a business man travels from Europe where GSM 900/1800 is installed, he might not be able to communicate with this mobile phone in the United States where GSM 1900 is used.
Accordingly, it is desired to provide a switchable transmitting stage for a mobile phone, which is able to switch between different GSM standards while at the same time the complexity of the mobile phone and the additional production costs are kept at a minimum.
The invention provides a switchable up-conversion loop device for the transmitting stage of a mobile phone having the features of claim 1.
The switchable up-conversion loop device for a transmitting stage of a mobile phone having multiple transmit frequency bands according to the present invention comprises a phase detector generating a phase detector output signal in response to the phase difference between an input signal and a mixing product signal, multiple switchable voltage controlled oscillators, each connected to the phase detector via a low pass filter for generating an output oscillation signal at a frequency which depends on the phase detector output signal, a coupling means for coupling the output oscillation signal to a mixer for mixing said output oscillation signal with a locally generated oscillating signal to produce said mixing product signal.
The principal idea of the present invention resides in that a plurality of switchable voltage controlled oscillators are provided in the up-conversion loop of a transmitting stage by means of which switching between the different transmit frequency bands is achieved.
Preferred embodiments of the present invention are listed in the dependent claims.
According to a preferred embodiment, the multiple switchable voltage controlled oscillators are switched on/off by means of a switching unit which connects/interrupts the supply voltage to said voltage controlled oscillators.
This has the advantage that reliable switching without additional switching components in the signal path is achieved.
According to a further preferred embodiment, the multiple voltage controlled oscillators are selected from a group consisting of a one-band voltage controlled oscillator covering one transmit frequency band and multiple-band voltage controlled oscillators covering a plurality of transmit frequency bands.
According to a further preferred embodiment, the multiple band voltage controlled oscillator is switchable between different transmit frequency bands in response to a band switch control signal.
This has the particular advantage that the switching is performed within one voltage controlled oscillator having a plurality of transmit frequency bands thus avoiding the necessity for a set of voltage controlled oscillators which leads to a reduction of production costs.
According to a further preferred embodiment, the band switch control signal is generated by a control unit.
According to a further preferred embodiment, the switching unit is connected to said control unit which connects/interrupts the supply voltage to said voltage controlled oscillators.
According to a further preferred embodiment, said multiple-band voltage controlled oscillator consists of an oscillator transistor and multiple resonance circuits which are switchable to said oscillator transistor by means of a switching element which is controlled by said band switch control signal.
According to a further preferred embodiment, the coupling means couples the output oscillation signal either inductively or capacitively to said mixer, and normally via a directional coupler which is transmission lines.
According to a further preferred embodiment, the mixer multiplies said locally generated oscillating signal with the signal received from said coupling means.
According to a further preferred embodiment, a loop filter is provided between said phase detector and said multiple switchable voltage controlled oscillators.
According to a further preferred embodiment, the input signal of the phase detector is generated by a modulator.
According to a further preferred embodiment, the modulator is a minimum shift keying modulator.
According to a further preferred embodiment, the frequency of the input signal and of the mixing product signal are both dividable by means of frequency dividing units which are controlled by said control unit.
According to a further preferred embodiment, said multiple band voltage controlled oscillator is a two-band voltage controlled oscillator covering two transmit frequency bands.
According to a further preferred embodiment, said multiple band voltage controlled oscillator is a three-band voltage controlled oscillator covering three transmit frequency bands.
According to a further preferred embodiment, the three one-band voltage controlled oscillators are provided and connected to the phase detector, wherein each one-band voltage controlled oscillator covers one transmit frequency band.
According to a further embodiment, there is provided one one-band voltage controlled oscillator covering one transmit frequency band and one two-band voltage controlled oscillator covering two transmit frequency bands, wherein both voltage controlled oscillators are connected to said phase detector via the low pass filter.
According to a further embodiment, there is provided one three-band voltage controlled oscillator covering three different transmit frequency bands, wherein the three-band voltage controlled oscillator is connected to said phase detector.
According to a further preferred embodiment, the transmit frequency bands are transmit frequency bands of a GSM system.
According to a further preferred embodiment, there are provided three different transmit frequency bands being the transmit frequency bands of GSM 900, GSM 1800 and GSM 1900.
According to a preferred embodiment, the output oscillation signal from the coupling means is amplified by a power amplifier.
According to a further preferred embodiment, the amplified output oscillation signal is input to an antenna switching unit which switches said amplified output oscillation signal to a transmitting antenna according to a control signal from said control unit.
According to a further preferred embodiment, the mixing product signal produced by the mixer is filtered by a low pass filter to suppress unwanted mixing products.
According to a further preferred embodiment, the locally generated oscillation signal is generated by a PLL-circuit in response to a control signal from said control unit.
According to a further preferred embodiment, the supply voltage of the pre-stage amplifier is switched on/off by a switch in response to a control signal from said control unit.