Surface acoustic wave driving circuit and oscillator therefor
A driving circuit of a surface wave resonator (X 1 ) is described; the resonator comprises a static capacitor (Co) and the driving circuit is adapted to supply a voltage (Vx) to the resonator. The driving circuit comprises reactive means (L 3 ) adapted to resonate in combination with said static capacitor (Co) of the resonator at a predetermined frequency (Fo) in the initial driving period of the resonator at said voltage; the driving circuit comprises passive means (R 3 ) adapted to determine oscillations at said predetermined frequency (Fo).
1. A surface wave resonator driving circuit, said resonator comprising a static capacitor and said driving circuit being adapted to supply a voltage to said resonator, wherein it comprises reactive means adapted to resonate in combination with said static capacitor of the resonator at a predetermined frequency of the initial driving period of the resonator at said voltage, said driving circuit comprising passive means adapted to determine oscillations at said predetermined frequency, and wherein said reactive means has a value so as to be essentially negligible with respect to the total reactance of the surface wave resonator after a predetermined initial period of time from the application of said voltage to said surface wave resonator.
2. The circuit according to claim 1 , wherein said passive means is adapted to force the surface wave resonator to essentially oscillate at said predetermined frequency after said predetermined initial period of time.
3. The circuit according to claim 1 , wherein said reactive means is an inductor.
4. The circuit according to claim 1 , wherein said passive means is a resistor.
5. The circuit according to claims 3 , wherein said inductor and said resistor are arranged in parallel and arranged in series to said surface wave resonator.
6. The circuit according to claim 5 , wherein it comprises a bipolar transistor having the collector terminal coupled to a supply power by means of another inductor, the base terminal coupled at a polarization voltage by means of another resistor, the emitter terminal coupled to ground by means of the parallel of a further resistor and another capacitor, said circuit comprising a further capacitor arranged between the collector terminal and the emitter terminal.
7. The circuit according to claim 6 , wherein it comprises a further inductor connected between said other capacitor and ground.
8. The circuit according to claim 2 , wherein said initial period of time is essentially 50 nanoseconds.
9. The oscillator comprising a surface wave resonator and a driving circuit as defined in claim 1 .