GB2128429A - An oscillator - Google Patents

Abstract

In conventional bulk acoustic wave oscillators waves are sent along a path through a suitable medium and are received to give a feedback signal. Oscillations occur whenever the path is an integral number of wavelengths long. However, they can occur at different side band frequencies, where each frequency gives a whole number of wavelengths along the path length. By employing this invention the side band frequencies can be inhibited. Bulk acoustic waves are launched from a transducer 2 and are reflected by a reflector 5, which acts in an analogous way to blazed optical diffraction gratings and reflects waves in a direction depending on their frequency. Waves at the desired frequency are sent to a second reflector 7, which is similar to the first, and are reflected to a second transducer 3, the output of which is the input to an amplifier 9. Part of the output of the amplifier 9 provides the input signal to the transducer 2. Any side band frequencies are reflected at 5 and 7 in directions such that they are not received at 3 and are therefore inhibited. <IMAGE>

Description

SPECIFICATION An oscillator This invention relates to an oscillator and particularly though not exclusively to bulk acoustic wave oscillators.

In conventional bulk acoustic wave oscillators waves are sent along a path through a suitable medium, such as quartz crystal, and are then received to give a feedback signal. Oscillations occur at frequencies such that the length of the path along which the waves travel is an integral number of wavelengths.

According to this invention there is provided an oscillator comprising: a transmitter for transmitting waves; deflection means arranged to deflect the waves in a direction depending on their frequency; a receiver for receiving waves after they have been deflected only in a certain direction or range of directions; and a feedback path from the receiver to the transmitter.

By employing this invention it is possible for an oscillator to be made to oscillate at only one selected frequency.

One way in which the invention may be performed will now be described by way of example with reference to the accompanying drawing which shows schematically an oscillator in accordance with the invention.

The illustrated oscillator comprises a quartz crystal 1 having first and second lithium niobate platelet transducers 2 and 3 respectively bonded to its surface. The first transducer 2 transmits bulk acoustic waves into the quartz crystal 1 where they follow a path 4, in the AT direction, shown as a broken line.

The bulk acoustic waves are incident on a first reflector 5 formed by a surface of the quartz crystal 1. This surface 5 has a stepped configuration, as illustrated, produced by ion beam milling. It acts in an analogous way to a blazed optical diffraction grating, reflecting acoustic waves of a particular frequency in a particular direction. The desired frequency at which the oscillator operates is such that the total path length followed by the waves in the quartz crystal 1 is an integral number of wavelengths long.

The first reflector 5 is arranged so that waves which have the desired frequency are sent in the BT direction along a path 6 to a second reflector 7, which is similar to the first. It causes further separation of the frequencies and reflects waves of the desired frequency along a path 8.

These waves are incident on the second transducer 3, normally thereto, which converts them into electrical signals. These are applied to the input of an amplifier 9 and constitute a feedback signal.

Part of the output signal of the amplifier 9 is taken along a line 10 and constitutes an input signal to the first transducer 2. The remainder of the output is taken from the circuit at 11.

By using the reflectors 5 and 7 only waves having the particular frequency at which the oscillator is required to operate are able to be received by the transducer 3. Other waves having different frequencies would either miss the transducer 3 altogether or would be incident on it at an angle such that they would not be detected by the transducer.

In alternative embodiments of the invention, instead of using reflectors the deflection means could be constituted by a transmission grating or other device for refracting the waves.

Claims

1. An oscillator comprising: a transmitter for transmitting waves; deflection means arranged to deflect the waves in a direction depending on their frequency; a receiver for receiving waves after they have been deflected only in a certain direction or range of directions; and a feedback path from the receiver to the transmitter.

2. A bulk acoustic wave oscillator constructed in accordance with claim 1.

3. A bulk acoustic wave oscillator as claimed in claim 2 and wherein the transmitter is an electroacoustic platelet transducer.

4. A bulk acoustic wave oscillator as claimed in claim 2 or 3 and wherein the receiver is an electroacoustic platelet transducer.

5. An oscillator as claimed in any preceding claim and wherein the deflection means includes a reflector.

6. A bulk acoustic wave oscillator as claimed in claim 5 when dependent on claim 2 and wherein the transmitter is arranged to transmit the waves into a body capable of conducting bulk acoustic waves and wherein the reflector is defined by a surface of that body.

7. An oscillator according to claim 5 or 6 and wherein the deflection means includes two reflectors.

8. A bulk acoustic wave oscillator substantially as illustrated in and described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION An oscillator This invention relates to an oscillator and particularly though not exclusively to bulk acoustic wave oscillators. In conventional bulk acoustic wave oscillators waves are sent along a path through a suitable medium, such as quartz crystal, and are then received to give a feedback signal. Oscillations occur at frequencies such that the length of the path along which the waves travel is an integral number of wavelengths. According to this invention there is provided an oscillator comprising: a transmitter for transmitting waves; deflection means arranged to deflect the waves in a direction depending on their frequency; a receiver for receiving waves after they have been deflected only in a certain direction or range of directions; and a feedback path from the receiver to the transmitter. By employing this invention it is possible for an oscillator to be made to oscillate at only one selected frequency. One way in which the invention may be performed will now be described by way of example with reference to the accompanying drawing which shows schematically an oscillator in accordance with the invention. The illustrated oscillator comprises a quartz crystal 1 having first and second lithium niobate platelet transducers 2 and 3 respectively bonded to its surface. The first transducer 2 transmits bulk acoustic waves into the quartz crystal 1 where they follow a path 4, in the AT direction, shown as a broken line. The bulk acoustic waves are incident on a first reflector 5 formed by a surface of the quartz crystal 1. This surface 5 has a stepped configuration, as illustrated, produced by ion beam milling. It acts in an analogous way to a blazed optical diffraction grating, reflecting acoustic waves of a particular frequency in a particular direction. The desired frequency at which the oscillator operates is such that the total path length followed by the waves in the quartz crystal 1 is an integral number of wavelengths long. The first reflector 5 is arranged so that waves which have the desired frequency are sent in the BT direction along a path 6 to a second reflector 7, which is similar to the first. It causes further separation of the frequencies and reflects waves of the desired frequency along a path 8. These waves are incident on the second transducer 3, normally thereto, which converts them into electrical signals. These are applied to the input of an amplifier 9 and constitute a feedback signal. Part of the output signal of the amplifier 9 is taken along a line 10 and constitutes an input signal to the first transducer 2. The remainder of the output is taken from the circuit at 11. By using the reflectors 5 and 7 only waves having the particular frequency at which the oscillator is required to operate are able to be received by the transducer 3. Other waves having different frequencies would either miss the transducer 3 altogether or would be incident on it at an angle such that they would not be detected by the transducer. In alternative embodiments of the invention, instead of using reflectors the deflection means could be constituted by a transmission grating or other device for refracting the waves. Claims

1. An oscillator comprising: a transmitter for transmitting waves; deflection means arranged to deflect the waves in a direction depending on their frequency; a receiver for receiving waves after they have been deflected only in a certain direction or range of directions; and a feedback path from the receiver to the transmitter.

2. A bulk acoustic wave oscillator constructed in accordance with claim 1.

3. A bulk acoustic wave oscillator as claimed in claim 2 and wherein the transmitter is an electroacoustic platelet transducer.

4. A bulk acoustic wave oscillator as claimed in claim 2 or 3 and wherein the receiver is an electroacoustic platelet transducer.

5. An oscillator as claimed in any preceding claim and wherein the deflection means includes a reflector.

6. A bulk acoustic wave oscillator as claimed in claim 5 when dependent on claim 2 and wherein the transmitter is arranged to transmit the waves into a body capable of conducting bulk acoustic waves and wherein the reflector is defined by a surface of that body.

7. An oscillator according to claim 5 or 6 and wherein the deflection means includes two reflectors.

8. A bulk acoustic wave oscillator substantially as illustrated in and described with reference to the accompanying drawing.