Modulators – Frequency modulator – Including stabilization or alternatively distortion – noise...
Reexamination Certificate
1999-12-06
2001-06-12
Grimm, Siegfried H. (Department: 2817)
Modulators
Frequency modulator
Including stabilization or alternatively distortion, noise...
C332S128000, C332S144000, C455S113000, C455S119000
Reexamination Certificate
active
06246297
ABSTRACT:
The present invention relates to a radio device comprising a frequency synthesizer for producing synthesized frequency signals, this synthesizer including a phase and/or a frequency modulation control for receiving a signal that presents a bandwidth called modulation bandwidth and this synthesizer being formed by at least two phase-locked loops.
The invention also relates to a method of phase and/or frequency modulating a frequency synthesizer.
Such devices are well known and find many applications, notably in the field of portable telephony devices that use a multitude of frequency channels determined by the synthesizer. One recollects that a synthesizer is, in essence, formed by a voltage-controlled variable oscillator intended to be slaved, by means of a phase-locked loop, to a frequency coming from a reference oscillator. A frequency divider is provided for finally determining the output frequency of the synthesizer.
One of the problems one is confronted with is the possibility of modulating the frequency and/or the phase of the variable oscillator. In effect, the presence of the phase-locked loop counterbalances the modulation, so that this modulation is hard to apply. Furthermore, one is also confronted with the problem of the phase noise that is generated by the digital frequency dividers the synthesizers habitually comprise working at a high frequency, for example, in the 800 MHz band.
From U.S. Pat. No. 4,409,563 is known to provide two loops for controlling the variable oscillator: one loop comprising a frequency discriminator and another loop comprising a phase discriminator. The loop comprising a frequency discriminator is used during a change of frequency or at the start, to facilitate the blocking of the variable oscillator to the reference oscillator, so that the loop comprising a phase discriminator can easily lock the variable oscillator. This known device is not at all confronted with the problem of the modulation of the variable oscillator.
The invention proposes a device in which are provided means for modulating the frequency and/or the phase of the variable oscillator while maintaining a satisfactory phase locking while ensuring a reduced level of phase noise.
Therefore, such a device is characterized in that at least a first phase-locked loop is provided of the high-pass type, and a second phase-locked loop of the low-pass type whose cut-off is smaller than said modulation band.
Thus, thanks to the invention, the basic frequency of the synthesizer is locked by the low-pass phase-locked loop, while this loop does not affect the modulation signals that are produced at a higher frequency. The phase noise is attenuated by the high-pass phase-locked loop.
The method according to the invention is characterized in that a first phase-locked loop is used of the high-pass type, and a second phase-locked loop of the low-pass type, whose cut-off is smaller than said modulation band.
REFERENCES:
patent: 4313209 (1982-01-01), Drucker
patent: 4409563 (1983-10-01), Vandegraaf
patent: 5485129 (1996-01-01), Franson et al.
patent: 5734302 (1998-03-01), Teng et al.
patent: 5790942 (1998-08-01), Le Corre et al.
Grimm Siegfried H.
Slobod Jack D.
U.S. Philips Corporation
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