Telecommunications – Receiver or analog modulated signal frequency converter – Signal selection based on frequency
Reexamination Certificate
1999-05-27
2001-04-10
Nguyen, Lee (Department: 2683)
Telecommunications
Receiver or analog modulated signal frequency converter
Signal selection based on frequency
C455S076000, C455S112000, C455S118000, C455S086000, C455S207000, C455S314000, C455S552100, C455S553100
Reexamination Certificate
active
06215988
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to radiotelephones and, in particular, to radiotelephones or mobile stations such as those capable of operation with a cellular network.
BACKGROUND OF THE INVENTION
The demand for so called dual mode terminals or stations is expected to increase with time. In the United States of America there is presently at least one system which supports dual mode operation, i.e., digital TDMA and analog FM, also referred to as DAMPS. As the systems such as GSM, PCS, DECT, DCS1800 and TDMA1900 become more widely used there is expected to be a need to have mobile stations which support two modes of operation, such as GSM and DCS1800 or DAMPS and TDMA1900 or DCS1900. A proposed third generation mobile telecommunication systems, such as UMTS (in ETSI) or FPLMTS (in CCIR), is under development. These advanced systems may also require some type of dual mode operation.
In an article entitled “GSM and DECT-A Dual Mode Solution”, Mobile Communications International 21, April 1995, pgs. 57-60, B. Rashidzadel et al. describe an RF subsystem in
FIG. 3
for a dual mode handset that operates in the GSM frequency band (890-960 MHz) and the DECT frequency band (1880-1900 MHz). In the transmitter portion a single I/Q modulator provides direct modulation at either the DECT or GSM frequency bands, and is connected through a SPDT switch to one of a DECT or a GSM transmitter chain. In the receiver portion separate DECT and GSM low noise amplifiers (LNAS) are used due to the large difference in frequencies. Following the GSM LNA and an image reject filter, the next stage is a dual stage downconversion device implemented as an integrated circuit chipset, e.g. Siemens PMB2402. In the DECT receiver, a number of currently available chipsets which employ an LNA and first downconversion stage are said to be suitable for use. A SPDT switch is employed to select one of the GSM or DECT receive chains for inputting to the last downconverter stage of the dual stage downconversion device. In this approach the second stage of the downconversion chip is common to both the GSM and DECT receive chains, which is said to result in a common second IF signal which can be digitally sampled, digitally filtered (depending on the mode of operation), and suitably demodulated.
In this approach a total of at least three local oscillator signals are required, one for the DECT downconverter, and two for the dual stage GSM, GSM/DECT downconverter. Also in this approach both the GSM and the DECT chains employ a double conversion superheterodyne receiver.
In commonly assigned Finnish Patent Application FI 961465 a dual band transmitter/receiver is disclosed that is based on direct conversion to baseband, wherein a single frequency synthesizer is used for both bands. When operating in the higher frequency band the output of the synthesizer is employed as the mixing frequency, while in the lower frequency band a mixing frequency is obtained by dividing the output frequency of the synthesizer by at least two.
OBJECTS OF THE INVENTION
It is a first object of this invention to provide a method for constructing and operating a dual band wireless user terminal, such as a personal communicator or a cellular telephone, so as to reduce the component count to achieve savings in cost, complexity, size, and power consumption.
It is a further object of this invention to provide a method for constructing and operating a dual band terminal so as to minimize a number of required frequency filters.
It is another object of this invention to provide a dual band terminal that requires but one band-switched UHF VCO, and that furthermore does not require multiplier or divider blocks to form mixing frequencies.
SUMMARY OF THE INVENTION
The foregoing and other problems are overcome and the objects of the invention are realized by a dual band user terminal that is constructed and operated in accordance with the teachings of this invention. The terminal includes a controller for outputting a BAND signal for specifying operation in one of a first frequency band or a second, higher frequency band; a single frequency synthesizer that is responsive to the BAND signal for outputting an RF signal in one of two frequency bands; and an RF transceiver comprising a dual band receiver that receives RF signals in the first frequency band and in the second, higher frequency band, and a dual band transmitter that transmits RF signals in the first frequency band and in the second, higher frequency band.
The dual band receiver includes a first receiver chain that operates in the first frequency band as a single conversion receiver (one IF) having a downconversion mixer that is preceded by a first filter and that is followed by second filter. The dual band receiver further includes a second receiver chain that operates in the second frequency band as a dual conversion superheterodyne receiver having a first downconversion mixer preceded by a first filter and followed by a second filter coupled to a second downconversion mixer followed by a third filter. The single downconversion mixer of the single conversion receiver is also the second downconversion mixer of the dual conversion superheterodyne receiver, and the second filter of the single conversion receiver is also the third filter of the dual conversion superheterodyne receiver. The second filter of the single conversion receiver has a center frequency in a range of approximately 45 MHz to approximately 60 MHz.
The dual band transmitter includes a modulator, specifically an IQ modulator, that modulates an input RF signal in accordance with information to be transmitted and that outputs a modulated RF signal. When operating in the first frequency band the input RF signal has a frequency that is equal to the transmitted RF signal, and when operating in the second frequency band the input RF signal has a frequency that is equal to one half of the transmitted RF signal. The dual band transmitter also includes an upconversion mixer that upconverts the modulated RF signal, using the input RF signal, to have a frequency equal to the transmitted RF signal when operating in the second frequency band.
In one embodiment of this invention the first filter of the single conversion receiver is also the second filter of the dual conversion superheterodyne receiver.
In both embodiments of this invention the first and second downconversion mixers of the dual conversion superheterodyne receiver are both supplied with the same mixing frequency from the single frequency synthesizer.
In a first embodiment of this invention the first frequency band includes 890-915 MHz and 935-960 MHz, and in a second embodiment the first frequency band includes 829-849 MHz and 869-894 MHz.
Also in the first embodiment of this invention the second frequency band includes 1710-1785 MHz and 1805-1880 MHz, and in the second embodiment the second frequency band includes 1850-1910 MHz and 1930-1990 MHz.
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“High Frequency Part Of A Real Time Test Mobile Station For UMTS System Evaluations”, Kari Lehtinen et al., 24thEuropean Microwave Conference, vol. 2, pp. 1575-1580.
“GSM And Dect-A Dual Mode Solution”, Rashidzadeh et al., Mobile Communications International 21, Apr. 1995, pp. 57-60.
Nguyen Lee
Nokia Mobile Phones Ltd.
Ohlandt Greeley Ruggiero & Perle LLP
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