Acoustic wave oscillator

Claim 2

An acoustic wave device including an acoustic wave delay line providing a feedback loop to an amplifier to form an oscillator, and a discriminator for providing a control signal to apply to phase shift circuitry in the feedback loop for varying the frequency of the oscillator, the delay line comprising a substrate able to support acoustic waves along a flat surface thereof, input and output transducers for launching and receiving acoustic waves in the substrate, the discriminator comprising at least one transducer arranged on the substrate to receive acoustic waves from the input transducer and provide a control signal which is substantially linear with frequency near the oscillator centre frequency.

Claim 3

An acoustic wave device according to claim 1 and further comprising a differential amplifier having one input connected to the discriminator and a second input to which modulated signals may be supplied, and having an output connected to the phase shift circuitry.

Claim 4

An acoustic wave device according to claim 1 wherein the discriminator comprises two transducers one having a centre frequency above the centre frequency of the oscillator and the other having a centre frequency below the centre frequency of the oscillator.

Claim 5

An acoustic wave device according to claim 1 wherein the discriminator comprises a single transducer whose centre frequency is different from that of the oscillator centre frequency and whose response is linear around the oscillator centre frequency.

Claim 6

An acoustic wave device according to claim 1 wherein the delay line has two output transducers spaced apart along a path of acoustic waves from the input transducer and wherein the two output transducers are connected to variable resistors whereby the phase of feedback to the amplifier may be varied to vary the oscillator frequency.

Claim 7

An acoustic wave device according to claim 3 and further comprising a discriminator differential amplifier having two inputs and an output, and wherein the inputs are connected one to each of the discriminator transducers and the output forms the control signal.

Claim 8

An acoustic wave device according to claim 6 and further comprising a differential amplifier having two inputs and an output, wherein one input is connected to the output of the discriminator differential amplifier and one input may have applied thereto a modulated signal, and wherein the output is connected to the phase shift circuitry.

Claim 9

A surface acoustic wave oscillator comprising: a piezoelectric substrate having a flat surface on which input and output interdigital comblike transducers are arranged to provide a feedback loop to an amplifier for causing oscillations thereof; phase shift circuitry in the feedback loop for varying the frequency of oscillation in response to a control signal; two interdigital comblike discriminator transducers arranged on the substrate for receiving surface acoustic waves from the input transducer, one of the discriminator transducers having a centre frequency below the oscillator centre frequency and the other of the discriminator transducers having centre frequency above the oscillator centre frequency; a discriminator differential amplifier having two inputs and output, the inputs being connected on to each of the discriminator transducers and the output providing a control signal; a further differential amplifier having two inputs and an output, one of the inputs being connected to the output of the discriminator amplifier output, and the other input arranged for supply with a modulated signal, and the output connected to the phase shift circuitry in the oscillator feedback loop.

Claim 10

A surface acoustic wave oscillator comprising: a piezoelectric substrate having a flat surface on which input and output interdigital comblike transducers are arranged to provide a feedback loop to an amplifier for causing oscillations thereof; phase shift circuitry in the feedback loop for varying the frequency of oscillation in response to a control signal; two interdigital comblike discriminator transducers arranged on the substrate for receiving surface acoustic waves from the input transducer, one of the discriminator transducers having a centre frequency below the oscillator centre frequency and the other of the discriminator transducers having centre frequency above the oscillator centre frequency; a discriminator differential amplifier having two inputs and output, the inputs being connected on to each of the discriminator transducers and the output providing a control signal; a further differential amplifier having two inputs and an output, one of the inputs being connected to the output of the discriminator amplifier output, and the other input arranged for supply with a modulated signal, and the output connected to the phase shift circuitry in the oscillator feedback loop.