Oscillators – Combined with particular output coupling network
Reexamination Certificate
1999-12-09
2001-10-09
Grimm, Siegfried H. (Department: 2817)
Oscillators
Combined with particular output coupling network
C331S096000, C331S175000, C333S112000
Reexamination Certificate
active
06300840
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microwave or millimeter-wave integrated circuit using a semiconductor substrate, commonly known as a microwave monolithic integrated circuit, and more specifically to an oscillation circuit for generating microwave or millimeter-wave signals with circuit operation stabilized according to load conditions.
2. Description of Related Art
Oscillators used in sensors and communications devices operating in the microwave and millimeter-wave bands, referred to below simply as high frequency bands, require a low phase noise characteristic. Phase noise in an oscillator is a variation in the oscillation frequency with a period longer than that of the oscillation frequency; low phase noise is indicative of stable oscillator operation. Factors contributing to phase noise include bias, thermal noise, and modulation caused by nonlinear operation of active elements.
Changes in load impedance can also cause the oscillation frequency of an oscillator to vary, a phenomenon known as pulling. To avoid problems caused by pulling, variations in load are removed by, for example, connecting the oscillator to an amplifier connected to multiple stages or to an isolator.
However, because of the difficulties in manufacturing a resonance circuit with a Q sufficiently high to assure stable oscillator operation in such high frequency band regions as the millimeter-wave band, oscillators operating in such high frequency bands are subject to even greater loads.
It is to be noted that use of Lange couplers is taught in Japanese Patent Laid-Open Publication Nos. 10-242719 and 6-177648, and Japanese Patent Laid-Open Publication 9-46225 teaches a common phase-locked oscillator (PLO).
SUMMARY OF THE INVENTION
With consideration for the above noted problem, an object of the present invention is to provide a microwave/millimeter-wave integrated circuit capable of maintaining stable oscillation by reducing time-based variation in load impedance.
To achieve this object, a microwave/millimeter-wave integrated circuit according to the present invention comprises an oscillator for generating and outputting a high frequency signal in the microwave/millimeter-wave band, and a Lange coupler, to an input terminal of which is input the high frequency signal output from the oscillator, and to an isolation terminal of which is connected a terminating resistance equal to a load impedance connected to an output terminal.
Preferably, this high frequency integrated circuit further comprises an amplifier for amplifying and outputting a high frequency signal output from the Lange coupler. In this case the output signal from the oscillator can be amplified while also improving the output characteristic.
Alternatively, a high frequency integrated circuit according to the present invention comprises an oscillator for generating and outputting a high frequency signal in the microwave/millimeter-wave band; and a directional coupler having a main signal line to one end of which the high frequency signal from the oscillator is input, and to the other end of which is connected a terminating resistor of a predetermined resistance. In this case, a high frequency signal output from the oscillator is input to one end of the main signal line of the directional coupler, and a terminating resistor of a specific resistance is connected to the other end of this main signal line. It is therefore possible to stabilize the load impedance of the oscillator, reduce variation in the oscillation frequency as a result of variation in load impedance, and thereby reduce phase noise.
This high frequency wave integrated circuit further preferably comprises an amplifier for amplifying and outputting a high frequency signal output from a sub-transmission line of the directional coupler. By thus using an amplifier, the output signal from the oscillator can be amplified while also improving the output characteristic.
A microwave/millimeter-wave integrated circuit for generating and outputting a high frequency signal in the microwave/millimeter-wave band according to a further aspect of the present invention has an oscillator for generating and outputting a high frequency signal in the microwave/millimeter-wave band; a directional coupler having a main signal line to one end of which is input the high frequency signal from the oscillator; an amplifier for amplifying and outputting a high frequency signal input from the oscillator through the main signal line of the directional coupler, and having a bias input terminal to which bias is input from an external source; and a phase detecting integrated circuit for phase detecting a signal reflected from the amplifier input through the sub line of the directional coupler, generating an inverse phase signal of which the phase is opposite the detected phase, and outputting the inverse phase signal to a bias input terminal of the amplifier.
With this aspect of the invention, a phase detector detects the phase component of the signal reflected from the amplifier and obtained through a directional coupler, and a signal inverting this detected phase is applied to the bias input terminal of the amplifier. Variation over time in the input impedance of the amplifier is therefore cancelled, change in the load impedance as a result of varying input impedance can be suppressed, and phase noise can thus be reduced.
A microwave/millimeter-wave integrated circuit according to yet a further aspect of the invention has an oscillator for generating and outputting a high frequency signal in the microwave/millimeter-wave band; and a phase shifter for shifting phase of a high frequency signal output from the oscillator to a predetermined phase setting.
By thus using a phase shifter to shift the phase of the oscillator output signal so that change in the oscillation frequency is gradual, a microwave/millimeter-wave integrated circuit according to this aspect of the invention can prevent variation over time in the load impedance connected to the phase shifter output, reduce change in the oscillation frequency as a result of varying input impedance, and thus reduce phase noise.
The predetermined phase to which the phase of the oscillator output signal is shifted is preferably a phase at which frequency change in high frequency signal output from the oscillator is smallest for a phase change induced by a load of a particular voltage standing wave ratio connected to the output terminal of the phase shifter. It is therefore possible to prevent time-based variation in the load impedance to the oscillator, reduce change in the oscillation frequency as a result of varying input impedance, and thus reduce phase noise.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 3973204 (1976-08-01), Keiter
patent: 4392115 (1983-07-01), Volluet et al.
patent: 4937541 (1990-06-01), Podell et al.
patent: 5159298 (1992-10-01), Dydyk
patent: 5294895 (1994-03-01), Feeney et al.
patent: 5504465 (1996-04-01), Yung et al.
patent: 6-177648 (1994-06-01), None
patent: 9-46225 (1997-02-01), None
patent: 10-242719 (1998-09-01), None
Kashiwa Takuo
Sasaki Yoshinobu
Tanahashi Naoki
Grimm Siegfried H.
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
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