Temperature compensated acoustic surface wave oscillator

Claim 2

An oscillator comprising a piezoelectric body having an acoustic surface wave propagation surface formed thereon, a first and a second pair of interdigital transduceRs, each said pair comprising a launching and a receiving transducer arranged on said acoustic surface wave propagation surface respectively to launch and receive acoustic surface waves in corresponding first and second acoustic surface wave propagation directions over said acoustic surface wave propagation surface, amplifying means connected respectively to amplify the output of the receiving transducer of each said transducer pair and to feed said amplified output to the corresponding said launching transducer to maintain a respective component oscillation in said pair, said first and second acoustic surface wave propagation directions being selected so that the corresponding temperature coefficients of the frequency of the respective component oscillation are of a significantly different non-zero value each of which is substantially constant with respect to normal manufacturing variations in the orientations of said transducers with respect to the crystallographic axes of said body, and output means for deriving an output oscillation whose frequency is either the sum or the difference of said component oscillations, the respective frequencies of said component oscillations being selected in relation to their temperature coefficients of oscillation frequency so that the temperature coefficient of said output oscillation is substantially zero.

Claim 3

An oscillator as claimed in claim 1, in which the amplification loop associated with at least one of said pairs of interdigital transducers includes phase adjustment means for adjusting the frequency of the output oscillation.

Claim 4

An oscillator as claimed in claim 1 in which said piezoelectric body is formed of lithium niobate.

Claim 5

An oscillator as claimed in claim 1, in which said piezoelectric body is formed of quartz.

Claim 6

A temperature compensated oscillator comprising, a crystal acoustic surface wave propagation substrate, a first pair of interdigital transducers comprising an input transducer and an output transducer disposed on said substrate to transmit and receive acoustic surface waves of a first frequency along a first propagation direction, a second pair of interdigital transducers comprising a second input transducer and a second output transducer disposed on said substrate to transmit and receive acoustic surface waves of a second frequency along a second different propagation direction, amplifier means connected to form first and second positive feedback loops between the output and input transducers of said first and second pairs of transducers, respectively, to maintain oscillations at said first and second frequencies, respectively, said first and second propagation directions being chosen so that the corresponding temperature coefficients of said first and second oscillation frequencies are substantially constant with respect to the crystal axes of the substrate, and mixing means coupled to the output of the amplifier means for deriving an output oscillation signal of the sum or difference frequency between said first and second oscillation frequencies, said first and second pairs of transducers and said substrate being chosen so that the first and second oscillation frequencies in relation to their respective temperature coefficients of oscillation frequency maintain the temperature coefficient of the output oscillation signal substantially zero.

Claim 7

A temperature compensated oscillator comprising, a crystal acoustic surface wave propagation substrate, a first pair of interdigital transducers comprising an input transducer and an output transducer disposed on said substrate to transmit and receive acoustic surface waves of a first frequency along a first propagation direction, a second pair of interdigital transducers comprising a second input transducer and a second output transducer disposed on said substrate to transmit and receive acoustic surface waves of a second frequency along a second different propagation direction, amplifier means connected to form first and second positive feedback loops between the output and input transducers of said first and second pairs of transducers, respectively, to maintain oscillations at said first and second frequencies, respectively, said first and second propagation directions being chosen so that the corresponding temperature coefficients of said first and second oscillation frequencies are substantially constant with respect to the crystal axes of the substrate, and mixing means coupled to the output of the amplifier means for deriving an output oscillation signal of the sum or difference frequency between said first and second oscillation frequencies, said first and second pairs of transducers and said substrate being chosen so that the first and second oscillation frequencies in relation to their respective temperature coefficients of oscillation frequency maintain the temperature coefficient of the output oscillation signal substantially zero.

Claim 8

A temperature compensated amplifier as claimed in claim 5 wherein the length of the interdigital electrode system of one transducer of said first pair of transducers is equal to the center-to-center spacing between the input and output transducers of said first pair of transducers.

Claim 9

A temperature compensated amplifier as claimed in claim 5 wherein said substrate is composed of lithium niobate and said mixing means derives an output oscillation signal that is the difference frequency of said first and second oscillation frequencies.

Claim 10

A temperature compensated amplifier as claimed in claim 4 wherein said substrate is composed of quartz and said mixIng means derives an output oscillation signal that is the sum frequency of said first and second oscillation frequencies.

Claim 11

A temperature compensated amplifier as claimed in claim 5 wherein said amplifier means includes adjustable phase shift means for adjusting the frequency of the output oscillation signal.