Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
1999-05-11
2001-06-26
Mis, David (Department: 2817)
Oscillators
Solid state active element oscillator
Transistors
C331S096000, C331S172000, C331S17700V
Reexamination Certificate
active
06252469
ABSTRACT:
TECHNICAL FIELD
The present invention relates to light and small-sized microwave/millimeter-wave injection locked oscillators for wireless communications, which have a good frequency stability and a high signal purity.
BACKGROUND ART
As the information content has increased in recent years, people have come to pay attention to personal communications in which a large volume of analog and digital information is transmitted at a high speed by radio by using high-frequency carriers such as microwaves or millimeter waves. In such communications, there is a demand for development of compact and light microwave and millimeter-wave signal generators having good frequency stability and little phase noise.
A conventional injection locked microwave signal generator is shown in FIG.
14
. The injection locked microwave signal generator is made up of a microwave and millimeter-wave amplifier
650
which operates at a fundamental oscillation frequency f′, a positive feedback loop
651
consisting of a delay line
652
and a combiner/divider
653
, and a microwave and millimeter-wave amplifier
655
. In an operation at a free oscillation time, first, a random noise inside the positive feedback loop
651
is amplified by the amplifier
650
, so that the noise level of the fundamental oscillation frequency f′ becomes high, and the random noise circulates through the positive feedback loop
651
. During repetition of the above process, owing to a signal of the fundamental oscillation frequency f′ and non-linearity of the amplifier
650
, harmonic components n×f′ (n: integer) of the fundamental oscillation frequency f′ grow at a frequency at which the phase rotational angle of the positive feedback loop
651
becomes 360°. Thus, in a steady state, a signal of the fundamental oscillation frequency f′ and its harmonics n×f′ (n: integer) are generated.
Then, by forcibly injecting a signal component having a stable frequency fo (fo=f/m (m: integer)) and a reduced phase noise from the input terminal
660
through the microwave and millimeter wave amplifier
650
, the signal having the free fundamental oscillation frequency f′ is locked to a signal having a frequency f which is m times the frequency fo of the injection signal. In this manner, it is possible to reduce the phase noise of the free fundamental oscillation frequency f′ and stabilize the frequency.
The operation is described below. The forced signal fo injected from the outside causes the signal having the frequency f, which is fo×m, to be generated owing to the non-linearity of the microwave and millimeter wave amplifier
655
. When the free fundamental oscillation frequency f′ is located in the neighborhood of the harmonic fo×m of the injection signal (f′≅f), the signal of the free fundamental oscillation frequency f′ is pulled in the harmonic fo×m (m: integer) of the injection signal into a signal locked to the harmonic signal fo×m . Then, the signal is outputted from the output portion
670
. Thus, it is possible to reduce the phase noise of the fundamental oscillation frequency f′ and stabilize the frequency.
In the method shown in
FIG. 14
, the phase is controlled by a line length of the positive feedback loop
651
including the delay line
652
and the combiner/divider
653
, and the fundamental oscillation frequency f′ is determined. When the frequency f′ becomes high, the line length of the positive feedback loop
651
becomes short and it becomes difficult to control the fundamental oscillation frequency f′. In such a circuit construction, owing to the characteristic of transmission between D and C of the combiner/divider
653
, the injection signal inputted thereto through the amplifier
655
is outputted to the output terminal
670
. Thus, the signal taken out from the output terminal
670
includes not only a desired wave but also many undesired waves. Further, basically, the fundamental oscillation frequency f′ cannot be varied, although changing the bias point of the amplifier
650
allows the frequency to be slightly changed.
The fundamental oscillation frequency f′ can be varied by setting the Q value of the positive feedback loop
651
to a small value thereby to widen the locking range at the injection locking time. But when the Q value of the circuit is small, the fundamental oscillation frequency f′ becomes unstable owing to influence by an environmental temperature and other factors. In this case, locking achieved by the signal injection becomes off when the locking range is exceeded. A stable injection locking can be achieved only in the vicinity of the center of the locking range. For such a reason, the circuit construction as mentioned above has problems that it is difficult to obtain a high-frequency wave such as millimeter waves, reduce signals including undesired waves, and vary frequencies.
DISCLOSURE OF THE INVENTION
Therefore, it is a primary object of the present invention to provide an microwave/millimeter-wave injection locked oscillator capable of reducing signals including undesired waves, widening the variable range of frequencies, and easily providing a high-frequency wave such as a millimeter wave.
It is a further object of the present invention to enable such a microwave/millimeter-wave injection locked oscillator to reliably generate a stable signal with a low noise, by making the phase constant in the locking range.
In order to achieve the above primary object, according to the present invention, without constituting a positive feedback loop, a reflection type voltage control oscillator capable of controlling a fundamental oscillation frequency f′ is prepared, which oscillator has a series arrangement in which a signal is directly injected into an active element section through a resonator.
That is, the present invention provides an microwave/millimeter-wave injection locked oscillator comprising an oscillation circuit having an active element section, a resonant circuit connected with the active element section at one side thereof and resonating at a predetermined frequency f, and a harmonic output circuit connected with the active element section at the other side thereof to fetch a signal having an nth (n: an integer) harmonic component of a signal having the frequency f from the resonant circuit; an injection circuit generating a reference signal for frequency-locking a signal in the resonant circuit; and an input means for inputting the reference signal to the resonant circuit.
In an embodiment, the resonant circuit includes a transmission line and a capacitance element. The input means is provided at one end of the transmission line or the capacitance element. The reference signal has a frequency component of f/m (m: an integer).
The injection circuit may include a crystal oscillator of a low frequency.
The injection circuit may have a signal generator and a wide-band non-linear amplifier having an amplification degree between a frequency of f/m and a frequency of nf.
The injection circuit may further comprise an h-multiplier (h: an integer) connected between the signal generator and the wide-band non-linear amplifier.
On the other hand, the capacitance element of the resonant circuit may be made up of two varactor diodes connected in series with each other in reverse orientations. Then, a signal outputted from the injection circuit is injected into a node between the two varactor diodes.
Alternatively, the capacitance element of the resonant circuit may be constituted of a microwave transistor between two terminals thereof, and a signal outputted from the injection circuit may be injected into the other terminal.
Further, the capacitance element of the resonant circuit may be constituted of two microwave transistors in which collector terminals and base terminals thereof are commonly connected, one emitter terminal is connected with a transmission line, and the other emitter terminal is grounded. Then, a signal outputted fr
Mis David
Sharp Kabushiki Kaisha
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