Dual mode mobile phone using a multiplex type filter

Details Dual mode mobile phone using a multiplex type filter Dual mode mobile phone using a multiplex type filter

1999-03-09

2001-06-19

Legree, Tracy (Department: 2681)

Telecommunications

Transmitter and receiver at same station

Radiotelephone equipment detail

C455S552100, C375S316000, C375S343000

Reexamination Certificate

active

06249687

ABSTRACT:

BACKGROUND OF THE INVENTION
Mobile phones for at least two frequency bands are already known. The Motorola Micro Tac 8900 mobile phone provides automatic shifting between the GSM 900 MHz band (global system for mobile communications) and the GSM 1800 MHz band.
From the EP 0 355 973 B1, a digital mobile phone is known. The digital mobile phone includes an antenna, a receiver input for receiving signals on a first frequency, and a transmitter output for transmitting signals on a second frequency, different from the first frequency. The digital mobile phones comprise a duplex type filter, having a reverse attenuation from the transmitter output to the receiver input. The duplex type filter is used to couple the antenna to said receiver input and transmitter output. The duplex type filter replaces thereby an antenna switch to couple the antenna to the receiver and the transmitter respectively, and its control logic.
SUMMARY OF THE INVENTION
In a mobile phone a duplex type filter and more generally a multiplex type filter may advantageously be used either in a multiband receiver or a multiband transmitter chain to reduce circuit complexity by saving switches and the accompanying control logic in the multiband receiver or transmitter chain and therefore to save space on the printed circuit board and costs.
Using known filter technologies as e. g. Surface Acoustic Wave (SAW) filters, it could be difficult to realize duplex type filters or multiplex type filters having widely separated passbands. Therefore, it may be a problem to secure high input impedance for the disparate bandpass filters in frequency bands outside of the corresponding passband. It is therefore an advantage, to use a matching circuit transforming a low input impedance of the corresponding bandpass filter to a high input impedance in the passbands of the other bandpass filters utilized in the multiplex type filter.
By using a transmission line for the matching circuit, circuit complexity may be further reduced and costs for unnecessary circuit components can be saved.


REFERENCES:
patent: 5388123 (1995-02-01), Uesugi et al.
patent: 5884149 (1999-05-01), Jaakola
patent: 6069923 (2000-05-01), Ostman et al.
patent: 6134427 (2000-10-01), Hughes
patent: 0 355973 B1 (1995-12-01), None

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