Tuners – Tuner unit directly responsive to voltage and/or current... – Reactance tuning
Reexamination Certificate
2000-03-09
2002-10-15
Graybill, David E. (Department: 2827)
Tuners
Tuner unit directly responsive to voltage and/or current...
Reactance tuning
C333S174000, C334S015000, C334S064000, C334S078000, C455S179100, C455S180400
Reexamination Certificate
active
06466114
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a resonator having variable resonance frequency and high Q-value, primarily intended for use on microwave frequencies and realized in MMIC-technology.
PRIOR ART
Resonators are a type of circuit which are common, for example, in oscillators, an oscillator often being formed by connecting a resonator to an amplifier. A resonator, as the name implies, usually comprises a resonator circuit, the resonance frequency of which decides the resonance frequency of the resonator and thus also of an oscillator formed by connecting the resonator to an amplifier.
A common requirement of an oscillator, and hence of the resonator belonging to the oscillator, is that it should be tunable, in other words that its resonance frequency should be able to be varied, across a broad frequency range. A further requirement is that the oscillator, across the whole of its frequency range, should have a high and relatively constant so-called Q-value, which, inter alia, gives the oscillator a low and even phase noise level. A precondition for achieving this is that the impedance of the resonator at its resonant frequency is relatively constant across its entire range of resonant frequencies. The resonant frequency is defined as the frequency for which the group delay has its maximum value.
Document GB 2 274 034 discloses a tunable voltage controlled oscillator with a circuit for connecting a tuning voltage to a resonator circuit, and does not disclose any means for keeping the impedance of the resonator at the resonant frequency constant across its range of resonant frequencies.
SUMMARY OF THE INVENTION
The problem which is solved by the present invention is therefore that of producing a resonator, the resonance frequency of which can be varied across a wide frequency range with essentially maintained impedance at its resonant frequency across its range of resonant frequencies.
This problem is solved according to the invention by means of a resonator with variable resonance frequency, intended for connection to an amplifier in order to form an oscillator with variable oscillation frequency, said resonator comprising a resonator circuit for deciding the resonance frequency of the resonator and thereby the oscillation frequency of the oscillator. The resonator circuit comprises at least a first inductance, at least a first variable capacitance, and means for varying the first capacitance. The resonator also comprises connection means for connecting the resonator to the amplifier, and is provided with means for varying the capacitance of the connection means in proportion to the variation of the first capacitance of the resonator circuit.
As stated above, it is desirable that a resonator according to the invention should have essentially constant impedance at resonance across the whole of its frequency range. Since the capacitance of the connection means according to the invention can be varied in proportion to the variance of the first capacitance of the resonator circuit, the impedance of the resonator can be kept essentially constant across the whole of the frequency range of the resonator. This is preferably achieved by the means for varying the capacitance of the connection means being arranged such that across all resonance frequencies, an essentially constant relationship is maintained between the capacitance of the connection means and the first capacitance of the resonator.
A further requirement of a resonator is that it should be screened from direct-current voltage components from an amplifier or other external devices to which the resonator is connected. This requirement is suitably achieved by having the connection means also comprise a non-variable capacitance.
The first capacitance of the resonator circuit preferably comprises two antiserially connected varactor diodes, which in their reverse directions are connected to a so-called sweep voltage, which is varied in order to get the combined capacitance of the varactor diodes to vary, thereby enabling the resonance frequency of the resonator circuit to be varied. Since the two varactor diodes are connected antiserially in relation to one another, the possibility is given of varying the resonance frequency across a very wide range, since the antiserial connection allows a very high alternating-current voltage across the varactor diodes without these starting to limit the signal amplitude by conducting current in their forward directions.
Suitably, the variable capacitance in the means for connecting the resonator to an amplifier also comprises a varactor diode, which in its reverse direction is connected to a sweep voltage which is varied in order to get the capacitance of the connection means to vary. That this varactor diode should be connected to the sweep voltage in its reverse direction is due to the fact that the intention is to use the varactor diode as a variable capacitance.
Since the capacitance of the varactor diode in the connection means, according to the invention, is varied in proportion to the variance of the first capacitance of the resonator circuit, the impedance of the resonator will be able to be kept essentially constant regardless of the changes to its resonance frequency. Since the varactor diode in the connection means also, as a result of its capacitance, will affect the resonance frequency of the resonator, it is advantageous if the sweep voltage to which the varactor diode in the connection means is connected is the same sweep voltage as that of the two antiserially connected varactor diodes in the first capacitance of the resonator.
The magnitude of the connection capacitance in a resonator according to the invention can be chosen relatively freely in relation to the first capacitance of the resonator circuit, since it is variable and since its size can be chosen independently from the size of the first capacitance of the resonator circuit pair.
In a resonator circuit in a resonator according to the invention, the first inductance can either be parallel-connected to the first capacitance or connected in series thereto. These variants of the invention will be described in greater detail below in the following sections of the present description.
The resonator according to the invention is preferably, but not necessarily, realized in MMIC-technology.
REFERENCES:
patent: 5291159 (1994-03-01), Vale
patent: 5379008 (1995-01-01), Bockelman et al.
patent: 5392011 (1995-02-01), Li
patent: 6084486 (2000-07-01), Suzuki et al.
patent: 2 241 846 (1991-09-01), None
patent: 2 274 034 (1994-07-01), None
patent: 2 276 786 (1994-10-01), None
Graybill David E.
Nixon & Vanderhye P.C.
Telefonaktiebolaget LM Ericsson (publ)
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