Low phase noise, wide tune range saw oscillators and methods of operating the same
First Claim
1. For use in an oscillator, a two port SAW resonator circuit for providing a tunable low phase noise oscillator signal comprising:
- a two port SAW resonator for which an equivalent circuit includes;
a motional inductance, a motional capacitance, and a motional resistance connected in series between the two ports, anda first parasitic capacitance between a first port of the SAW resonator and a common voltage;
a first inductance coupled between the first port of the SAW resonator and the common voltage, wherein the first inductance is sized to approximately offset a reactance of the first parasitic capacitance at a selected frequency;
a first variable tuning capacitance coupled between the first port of the SAW resonator and a first port for the SAW resonator circuit; and
an output port operable to be coupled to a load providing an impedance lower than an impedance of the first parasitic capacitance.
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Accused Products
Abstract
A two port, single pole SAW resonator is employed for a local oscillator to eliminate the secondary frequency responses of the prior art without adding additional inductances and capacitances within an amplifier stage. The stray capacitance which is seen within the equivalent circuit of a single pole, two port SAW resonator at a port for the SAW resonator is tuned out by coupling an appropriately sized inductance in parallel with that stray capacitance. Access to the series resonator within the SAW resonator equivalent circuit is thus provided, permitting direct tuning of the resonant frequency for the SAW resonator. The high Q of the SAW resonator ensures low phase noise/edge jitter, while direct tuning of the series resonator enables a wide tune range. The tunable SAW resonator circuit is thus well-suited for use in a low phase noise tunable oscillator employed, for instance, in clock recovery within SONET applications.
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Citations
20 Claims
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1. For use in an oscillator, a two port SAW resonator circuit for providing a tunable low phase noise oscillator signal comprising:
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a two port SAW resonator for which an equivalent circuit includes; a motional inductance, a motional capacitance, and a motional resistance connected in series between the two ports, and a first parasitic capacitance between a first port of the SAW resonator and a common voltage; a first inductance coupled between the first port of the SAW resonator and the common voltage, wherein the first inductance is sized to approximately offset a reactance of the first parasitic capacitance at a selected frequency; a first variable tuning capacitance coupled between the first port of the SAW resonator and a first port for the SAW resonator circuit; and an output port operable to be coupled to a load providing an impedance lower than an impedance of the first parasitic capacitance. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A two port SAW resonator circuit comprising:
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a two port SAW resonator having a passband; a first inductance coupled between the first port of the SAW resonator and a common voltage, the first inductance sized to resonate at frequencies within the passband with a first parasitic capacitance for the SAW resonator; a first variable tuning capacitance coupled between the first port of the SAW resonator and a first port for the SAW resonator circuit; and an output port operable to be coupled to a load providing an impedance lower than an impedance of the first parasitic capacitance. - View Dependent Claims (10, 11, 12, 13, 14)
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15. A two port SAW resonator circuit comprising:
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a two port SAW resonator having a passband with a center frequency; a first inductance coupled between the first port of the SAW resonator and a common voltage, the first inductance sized to resonate at the center frequency with a first parasitic capacitance for the SAW resonator; a first variable tuning capacitance coupled between the first port of the SAW resonator and a first port for the SAW resonator circuit; and an output port operable to be coupled to a load providing an impedance lower than an impedance of the first parasitic capacitance. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification