Radio transceiver with two frequency bands

Details Radio transceiver with two frequency bands Radio transceiver with two frequency bands

1998-11-12

2002-09-10

Patel, Ajit (Department: 2664)

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

C370S343000

Reexamination Certificate

active

06449264

ABSTRACT:

TECHNOLOGICAL FIELD
The present invention relates generally to the structure of a radio transceiver. Particularly, the invention relates to the structure of a high frequency part and intermediate frequency part of a radio transceiver, and to the selection of frequencies according to which it is possible to realize a device working in two frequency bands in an economical way.
BACKGROUND OF THE INVENTION
In addition to the present cellular radio systems, new systems are being built in which the frequency band usually differs from that used in the old system and which, at least partly, operate in the same region with the old systems. Further, cellular radio systems operating in different frequency bands are already used in various parts of the world. From the user's point of view, it would be advantageous if one single terminal (such as a mobile phone) could operate in several systems of different frequency bands in accordance with the user's selection or a command given by the network. Important combinations of two systems and frequency bands are GSM and DCS1800 (Global System for Mobile telecommunications; Digital Communications System at 1800 megahertz). One form of DCS1800 is also called PCN (Personal Communications Network); in the present patent application, DCS1800 is called DCS for short. The transmission frequency band for a GSM terminal is 890-915 MHz, and the reception frequency band 935-960 MHz. The respective transmission frequency band for DCS is 1710-1785 MHz, and the reception frequency band is 1805-1880 Mz. For GSM, the band width or the extent of the transmission and reception frequency bands is 25 MHz, and 75 MHz for DCS; the duplex interval is respectively 45 MHz for GSM and 95 MHz for DCS. The simplest way to implement a radio transceiver with two frequency bands is to redouble all radio and intermediate frequency parts between the antenna and the baseband interface. However, this solution is relatively expensive and space consuming. A natural direction to find a more economical solution is to try to use as many common intermediate frequency parts as possible in both systems.
The Finnish patent application No. 941862 (Nokia Mobile Phones Ltd.) and the corresponding EP patent application published with the number EP-0 678 974, disclose a radio transceiver according to
FIG. 1
operating in two frequency bands. Here the reception frequency signal FRX
1
or FRX
2
is first mixed to a first intermediate frequency IF
1
in a mixer
4
by using the first mixing frequency LO
1
, and then to a second intermediate frequency IF
2
in a mixer
6
by using a second mixing frequency LO
2
. Additionally, a third mixing frequency LO
3
is used in demodulator
12
to demodulate the signal. The first and second intermediate frequencies remain unchanged irrespective of the frequency band one operates in. A different first mixing frequency is generated in accordance with the frequency band the radio transceiver operates in. For the generation of different first mixing frequencies, the apparatus has two separate UHF (Ultra High Frequency) frequency synthesizers
13
and
30
. The abbreviation VCO in the figure stands for Voltage Controlled Oscillator. A common phase locked loop (PLL)
15
is used for adjusting the VCO frequencies. From the first intermediate frequency mixer
4
onwards, the same parts may be used in the receiver and, for example, it is not necessary to alter the second mixing frequency LO
2
when transferring from one frequency band to another. A common modulator
21
is used for transmitting the signal, for which the necessary modulation frequency is obtained by dividing the second mixing frequency LO
2
by an integer N in divider
33
; further, a mixer
20
is used to which the said first mixing frequency LO
1
is led as the mixing frequency. The radio frequency of a signal FTX
1
or FTX
2
to be transmitted is determined by which of the VCOs
13
,
30
is used to generate the mixing frequency. Because of the two UHF-VCOs
13
and
30
, this kind of apparatus requires relatively much current, its structure is large, it causes problems for the layout design, and it is expensive to manufacture.
The European published application No. EP 0 653 851 discloses a radio transceiver with two frequency bands in accordance with
FIG. 2
, containing only one UHF frequency synthesizer
31
. The first mixing frequency LO
1
generated by it is selected so that it is situated half-way between the two frequency bands in which the apparatus is supposed to operate. The publication presents an example in which the upper frequency band is 1710-1900 MHz, and the lower band is 890-960 MHz so that the first mixing frequency LO
1
varies between 1290 and 1500 MHz, and the first intermediate frequency IF
1
is 400 MHz. Consequently, when mixing onto the first intermediate frequency, lower LO injection is used for the first (higher) frequency band, and upper LO injection is used for the second (lower) frequency band. However, the problems related to this solution include the relatively wide tuning range required for the frequency synthesizer (at least 15% of the medium frequency of the frequency synthesizer) and the frequency hop which comes into question in such Time Division Duplexing (TDD) where different frequencies are used for reception and transmission. A specific feature of
FIG. 2
is the use of the same mixer
30
both in transmission and reception. Switches
32
and
33
are used for separating reception and transmission from each other, and the switch
32
is additionally used for selecting the frequency band. Block
40
comprises intermediate frequency parts including e.g. the second intermediate mixer, and block
41
comprises the usual demodulation, decoding and D/A conversion parts. Block
43
comprises the A/D conversion needed for the transmission, and coding, and block
42
comprises the modulation needed for the transmission.
SUMMARY OF THE INVENTION
The object of the present invention is to introduce a new structure for a radio transceiver with two frequency bands, which is small and economical to manufacture, and which is suitable for use in a case when time division multiplexing is used in at least one of the two frequency bands.
These objects are achieved by selecting the mixing and intermediate frequencies so that the first mixing frequency of the receiver may, in a radio system of the first frequency band, be derived from the corresponding frequency of the second frequency by simple calculation process.
The radio transceiver of the invention is intended to be used for the reception and transmission of radio signals in two frequency bands, and it comprises a first signal input for the reception of radio signals in the first frequency band, and a second signal input for the reception of radio signals in the second frequency band. The invention is characterized in that it comprises
a first mixer connected to the first signal input for mixing the radio signals of the first frequency band onto a predetermined first intermediate frequency;
a second mixer for mixing said first intermediate frequency onto a predetermined second intermediate frequency; and
a third mixer connected to the second signal input for mixing the radio signals of the second frequency band onto a predetermined frequency which is substantially the same as said second intermediate frequency.
In a radio transceiver apparatus of the present invention, there is provided one UHF frequency synthesizer for generating the first mixing frequency, the frequency of the synthesizer being adjustable in a known way within a certain tuning range. The limiting values for the tuning range are selected so that, by adjusting the first mixing frequency, the receiver may be tuned in a known way to all frequencies in use in a first radio system. A block carrying out a certain simple operation, such as the division or multiplying of the frequency, may be connected in series with the UHF frequency synthesizer. The operation is selected so that, for tuning the receiver to frequencies used in a second radio syste

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