Oscillators – Automatic frequency stabilization using a phase or frequency... – Plural oscillators controlled
Patent
1998-12-24
2000-08-15
Mis, David
Oscillators
Automatic frequency stabilization using a phase or frequency...
Plural oscillators controlled
331 14, 331 16, 331 17, 331 18, 331 23, 331 25, 327147, H03L 707, H03L 718, H03L 722, H03J 718
Patent
active
061042501
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for controlling a radar oscillator for generating a linear frequency sweep by employing a phase-locked loop. The method and the apparatus are intended for use in the traffic field, preferably in a radar of the FM/CW type, and can, for example, be part of a car radar system.
In the application fields mentioned above, it is desirable to achieve extremely linear frequency sweeps within a broad bandwidth area. Inadequacies of the controlled oscillator must not damage the linear sweep.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method and an apparatus which fulfil the desirable characteristics mentioned above. The object of the invention is achieved by a method and an arrangement which employ at least two phase-locked loops. One of the phase-locked loops, the linearization loop, is utilized to generate a linear frequency sweep and the other phase-locked loop, the oscillator loop, utilizing the linear sweep generated in the linearization loop as a reference signal.
According to the invention, two phase-locked loops are employed. One of the phase-locked loops, the linearisation loop, has a narrow bandwidth and provides considerable suppression of undesirable signals. The oscillator signal generated in the linearization loop is subsequently utilized in the second phase-locked loop, the oscillator loop, which has a much broader bandwidth. By virtue of the broad bandwidth of the oscillator loop, phase noise, among other things, is suppressed in the controlled oscillator.
According to the invention, the linearization loop advantageously has a bandwidth in the kHz range, typically between about 10 and about 100 kHz.
Furthermore, according to the invention the oscillator loop advantageously has a bandwidth in the MHz range, typically between about 5 and about 20 MHz, specifically about 10 MHz.
The oscillator frequency is preferably in the GHz range, typically between 70 and 80 GHz.
According to an advantageous method, the linear frequency sweep generated in the linearization loop is generated at a lower frequency than the oscillator frequency for the controlled oscillator. Thereby, the linearization loop is allowed to work more slowly, which places less demand on the components which are included in the linearization loop. The lower frequency for the linearization loop is advantageously between about 100 and 1000 MHz, preferably between about 500 and about 700 MHz.
According to an advantageous embodiment, the linearization loop comprises a phase detector, whose output by the intermediary of a loop filter is coupled to a control input on the oscillator of the linearization loop and whose one input is coupled to a clock reference and the other input is connected to the output on the oscillator of the linearization loop via a variable frequency divider. In this connection, the variable frequency divider advantageously consists of an l
counter. The introduction of digital means allows an extremely linear ramp to be generated on the output of the oscillator of the linearization loop.
According to a preferred embodiment, the counting interval n of the l
counter is adapted to be changed in a set pattern.
According to yet another embodiment of the arrangement according to the invention, the oscillator loop comprises a phase detector, whose output is coupled to the controlled oscillator via a loop filter and whose one input is connected to the output on the oscillator of the linearization loop via a first frequency divider and whose other input is connected to the output on a mixer via a second frequency divider, which mixer on the input side is connected to the output on the controlled oscillator and the output on another oscillator. Because of the large bandwidth of the oscillator loop, high suppression of phase noise in the oscillator is achieved. In addition, the oscillator frequency becomes independent of variations in the load impedance, so-called pulling.
BRIEF DESCRIPTION OF THE DRAWINGS
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REFERENCES:
patent: 4320355 (1982-03-01), Kawagoe et al.
patent: 4488123 (1984-12-01), Kurihara
patent: 5130670 (1992-07-01), Jaffe
patent: 5233351 (1993-08-01), Gregory et al.
Eckersten Christer
Olofsson Joakim
Celsiustech Electronics AB
Mis David
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