Telecommunications – Transmitter and receiver at same station – With frequency stabilization
Reexamination Certificate
1998-09-09
2002-04-09
Kincaid, Lester G. (Department: 2682)
Telecommunications
Transmitter and receiver at same station
With frequency stabilization
C455S077000, C455S183100, C455S260000, C455S552100
Reexamination Certificate
active
06370360
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the technical field of arrangements and methods for radio communication in frequency ranges divided into channels, and more specifically to the part of this field concerning channel selection in the frequency ranges.
BACKGROUND
The radio frequency spectrum is divided into frequency ranges utilized for different applications, for example, sound radio, television, mobile telephony, satellite communication, radar, and air and sea radio. Often these frequency ranges are in turn divided into a number of channels on which independent information may be transmitted. The frequency spacing between the channels in a frequency range is normally referred to as channel spacing, or carrier separation. A number of the frequency ranges used for mobile telephony are divided into channels in this way, for example, the mobile telephony systems Advanced Mobile Phone Service (AMPS), Global System for Mobile Communication (GSM) and Personal Communications System 1900 (PCS 1900). The channel spacing may, however, differ between the systems.
The same frequency range is sometimes used for different applications, and the channel spacing may differ for different applications. Usually, however, the same frequency range cannot be used for different applications at the same time in the same geographical area, since the signals associated with the different applications would disturb each other.
In radio communication in a frequency range divided into a number of channels it must be possible to select, with high precision, the channel that is to be used for reception or transmission at a given time. An early type of receiver (from the 1920s) was the so called straight receiver. In the straight receiver the channel selection is made using bandpass filters having variable centre frequencies. It is, however, hard to design variable bandpass filters having a good selectivity, since the centre frequency is varied over a larger frequency range. Today, therefore, the channel selection at reception is made in another way. One way is to use filters having fixed frequency characteristics and good selectivity and frequency displace the received radio frequency signals instead, using oscillator signals, the frequency of which has been selected with respect to the channel to be selected and the frequency characteristics of the filters. For example, the channel selection in a superheterodyne receiver or a homodyne receiver is based on these principles. Oscillator signals can also be used for channel selection at transmission, for example when mixing a modulated baseband or intermediate frequency signal to the desired channel in the radio frequency range.
When selecting channels for reception and/or transmission in a certain frequency range, there is therefore a need to be able to generate oscillator signals for which the mutual frequency difference between the oscillator signals corresponds to the channel spacing in the frequency range. Frequency synthesizing circuits for this purpose have, of course, been developed. One type of frequency synthesizing circuit is called a phase locked loop (PLL). With a conventional type phase locked loop oscillator signals having a frequency according to {fraction (N/R)}f
ref
, N and R being arbitrary integers, may be generated using a reference frequency. To be able to generate oscillator signals for channel selection in a frequency range with a certain channel spacing using such a phase locked loop the reference frequency should be divisible by the channel spacing, if a low noise level and a good loop bandwidth are to be achieved. If the available frequency, which is to be used as a reference frequency is not divisible by the channel spacing, it may be multiplied, using a frequency multiplier, by a suitable integer K. A disadvantage of this solution is that the frequency multiplier requires space and power. Another disadvantage is that there is a risk that the reference frequency obtained from the frequency multiplier is too high to be feasible for use in circuits currently available. This risk is particularly high if there is a need to generate oscillator signals for channel selection in several frequency ranges with different channel spacing.
Another type of frequency synthesizing circuit is a so called fractional-N PLL. From a reference frequency fref, using a fractional-N PLL circuit, it is possible to generate oscillator signals, having frequencies according to
N
+
F
/
Q
R
f
ref
,
N, F, Q and R being freely selectable integers. Fractional-N PLL circuits are usually used to achieve a faster adjustment of the frequency of the oscillator signals, which is an advantage for applications using frequency hopping. One example of a design of a fractional-N PLL circuit is given in the Patent Specification GB, A, 2091960.
Patent Specification WO, Al, 96/08883 describes how a fractional-N PLL is used in a dual-mode radio telephone. It is to be possible to use the radio telephone both in GSM (with a channel spacing of 200 kHz) and in satellite communication (with a channel spacing of 5 kHz). The intention is to be able to generate oscillator signals for channel selection with large channel spacing (GSM) and short channel spacing (satellite) in an efficient way. The document shows a frequency synthesizing circuit utilizing combinations of fractional-N PLL and so called Vernier loop techniques. (In Vernier loop techniques two phase locked loops are used having slightly different comparator frequencies, which enables the generations of oscillator signals for channel selection for channel spacings corresponding to the difference frequencies between the comparator frequencies) to obtain frequencies for both the communication systems. The design may also be used in a situation in which the available reference frequency is not divisible by all the channel spacings. This design, however, has disadvantages. The design is relatively complicated, requires a lot of space and relatively high currents and power.
SUMMARY OF THE INVENTION
The present invention relates to a radio communication unit comprising radio communication means for communication (reception and/or transmission) in one or more frequency ranges with associated channel spacing. The radio communication means utilize oscillator signals for channel selection in the frequency ranges. The radio communication unit further comprises a system clock generating a clock signal of a predetermined frequency not divisible by all the channel spacings. A first problem attacked by the invention is to obtain, in such a radio communication unit, a frequency synthesizer circuit that may be used for generating the oscillator signals utilized by the radio communication means for channel selection in all the frequency ranges. Another problem attacked by the invention is that the frequency synthesizing circuit is to be small and consume little power and current.
The problems stated above are solved, in general, in that the radio communication unit comprises a frequency synthesizing circuit in the form of a fractional-N PLL circuit, the fractional-N PLL circuit being arranged to utilize the clock signal as a reference frequency signal.
The purpose of the invention is thus to utilize the possibility of frequency division by rational number offered by a fractional-N PLL circuit, to enable the utilization of the available clock signal as a reference frequency signal even though the frequency of the clock signal is not divisible by all the channel spacings. The invention also comprises the use of such a radio communication unit and a radio telephone comprising such a radio communication unit.
The problems stated above are solved more specifically by a fractional-N PLL circuit having one or more controllable oscillators. The controllable oscillators are connected to the radio communication means and the oscillator signals generated by the controllable oscillators are used for channel selection in the radio communication means. The fractional-N PLL circuit controls the controllable oscillators so that osillator sign
Jenkens & Gilchrist
Kincaid Lester G.
Telefonaktiebolaget LM Ericsson
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