Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1999-11-12
2002-08-13
Nguyen, Lee (Department: 2683)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S076000, C455S085000, C455S086000, C455S553100
Reexamination Certificate
active
06434401
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The object of the present invention is a method for setting the operating frequencies of a multiband mobile telephony telephone and a telephone thus obtained. It can be used chiefly in the field of mobile telephony when it is necessary to go from a given frequency band to another given frequency band, in most cases according to another standard for the encoding of transmitted messages. The aim of the invention is to reduce the cost of manufacture of a multiband telephone of this kind.
In the field of radiocommunications, there is a known standard called the GSM standard in which the messages are broadcast by base stations and/or mobile telephones in the 900 MHz range. Furthermore, there is the known DCS standard in which the frequency range is about 1800 MHz. There also exists the PCS range in which this frequency band is 1900 MHz. There is also the UMTS standard in which the frequency band is 2200 MHz. The existence of all these bands or other future ones of course favours the multiplicity of communication networks and, hence, a greater possibility, in terms of frequencies, of users being connected with one another.
In addition to different frequency bands, there are transmission channel division modes of the time, frequency or coding type such that it is possible to convey various, simultaneous communications from one and the same base station and in one and the same geographical domain. The transmissions thus are of the TDMA, FDMA or CDMA type or, again, of the combined type. These terms signify Time Division Multiple Access, Frequency Division Multiple Access and Coded Division Multiple Access, translated in French as Accès Multiple à Répartition dans le Temps, Accès Multiple à Répartition en Frequence, or Accès Multiple à Répartition de Codage, AMRT, AMRF, and AMRC. The invention can be applied whatever the mode of transmission from this viewpoint.
The instruments referred to are obviously transmitters-receivers and must comprise a transmission and a reception chain. The base stations often comprise, in fixed positions, the same blocks and components as mobile telephones since the latter are mass produced and therefore inexpensive. For this reason, the invention relates to mobile telephony telephones whether these telephones are themselves mobile or not.
In such telephones, on the basis of a common antenna, a device is used to separate a reception channel from a transmission channel. In the transmission channel, given a frequency agility that is generally implemented in methods of mobile telephony, it is the common practice to make a transmitter with three oscillators. A first oscillator, which is an output oscillator, produces a signal at a transmission frequency. This transmission signal is furthermore mixed in a mixer with a signal produced by an oscillator producing a signal at a transition frequency. The mixer produces a difference signal having a frequency that corresponds to the difference between the transmission frequency and the transition frequency. This difference signal is then compared with a signal produced by a third oscillator at intermediate frequency. To put it in precise terms, the intermediate frequency produced by the third oscillator may be in the range of 200 MHz and the difference between the transmission frequency and the transition frequency is in the same range. It is then enough to work on the transition frequency to prompt changes, from one frame to another or periodically, in the transmission frequency and to maintain the required agility.
The problems of this type of operation are numerous. One of them is related to the great difference in frequency that exists between the different standards. Indeed, from the GSM standard to the DCS standard, the frequency is quite simply doubled. In addition, the frequency excursions used to achieve frequency agility, which are themselves standardized, are quite considerable. Thus, for the GSM standard, the dynamic range of frequency (in transmission or in reception) is 35 MHz. For the DCS and PCS standards it is 75 MHz and 60 MHz respectively.
For a single-band apparatus furthermore, one and the same transition frequency oscillator is used in the reception channel. In this case, the signal that it produces is mixed in a reception mixer with the received signal. The reception mixer then produces a signal whose frequency is substantially equal to the frequency of the intermediate frequency oscillator so as to enable immediate demodulation in base band. Thus, the number of mixers and the number of the demodulations are limited.
By way of an indication, a separation between the frequency band allocated to transmission and the frequency band allocated to reception is equal to 10 MHz in the GSM standard, 20 MHz in the DCS standard and in the PCS standard. This ultimately means that the transition frequency oscillators must be capable of a dynamic range respectively of 80 MHz (35 plus 10 plus 35), 170 MHz (75 plus 20 plus 75) and 140 MHz (60 plus 20 plus 60) for these three standards respectively. Given these very significant excursions (which are in the range of 10% of the nominal frequency of the oscillator), it does not appear to be possible, in the present state of the technology of manufacture of these oscillators, to make them cover two bands, even the two closest ones (DCS and PCS). To make them cover a single band is already a problem.
Indeed, for high quality service with a mobile telephone, the spectral purity of these oscillators has to be higher than −87 dBc/Hz to 10 KHz of the carrier, higher than −107 dBc/Hz to 100 KHz of the carrier and higher than −140 dBc/Hz to 3 MHz of the carrier. The frequency setting range of the oscillator at the transition frequency is theoretically between 1 and 2 GHz. In fact, the complexity of these oscillators, for GSM, DCS and PCS applications, leads to their being placed in three categories.
A first category lists the voltage-controlled oscillators known as non-adjusted oscillators. For these oscillators, only the controlled voltage makes it possible to compensate for the dispersion of characteristics of their components, and to work on a certain frequency band around an imposed base frequency. In the mobile telephones today, the supply voltage is about 3 volts. Indeed, they use three battery elements, giving 3.6 volts in rated voltage. A regulator reduces this voltage to three available volts. The useful controlled voltage is then between 0.5 and 2.5 volts. Given the compensation for the dispersion of the characteristics by the voltage, this voltage range cannot be exploited to the full extent and, in practice, the frequency band around an imposed base frequency can only be about 40 MHz. These first category oscillators are also the least expensive ones.
A second category lists the oscillators known as adjusted oscillators. For these oscillators, the dispersion of the characteristics due to their components is compensated for by preliminary settings. The controlled voltage is used however used to compensate for the temperature dispersions. In this case, for one and the same range of control voltage of 2 volts, it is possible to have a working range of 100 MHz around an imposed base frequency.
In a third category, the useful band is further increased around a base frequency imposed in two ways. Either a resonator of the oscillator is switched over or the range of control voltage is increased. The switching over of an element in the oscillator makes it possible to have a second band. Since this switched element is not adjusted, it is difficult to achieve high precision. Furthermore, if an element of this kind is very important, it adds a temperature drift in the oscillation frequency. For this reason, the frequency leap is limited. The two bands must remain within a limited band. For one and the same range of control voltage of 2 volts, there is thus obtained a range of operation of 220 MHz. Comparable results are obtained by using a voltage multiplier. The oscillator does not become more complex,
Nguyen Lee
Nilles & Nilles SC
Sagem SA
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