GB1490959A - Electrical oscillators - Google Patents

Abstract

1490959 Oscillators; surface wave devices MULLARD Ltd 16 Feb 1976 05967/76 Headings H3T and H3U A surface acoustic wave oscillator designed to have improved frequency stability, comprises a plate 1, e.g. of piezoelectric quartz of lithium niobate, Fig 3, having means 10-16 on two opposed major surfaces adapted to interact with surface acoustic waves and defining on each surface at least one distance D, the said means being connected in a circuit, Fig. 5, such that the distances defined on both surfaces are effective in determining the frequency of the oscillator, whereby bending of the plate 1 produces opposed changes in the distances defined on the two surfaces, and consequent changes in the frequency of the oscillator are small. In the embodiment of Fig. 3 a resonant cavity is formed on each surface by pairs of grating reflectors 10, 11 and 14, 15 made up of elements 13 which may be grooves or conducting strips. If the effective cavity lengths are D on both surfaces of the plate when undistorted, bending which increases one length to D + #D will decrease the other length to approximately D-#D. Interdigital transducers 12, 16 couple the cavities in parallel into a feedback path of an amplifier which may comprise the circuit of Fig. 5, or alternatively may be a tunnel diode negative resistance amplifier, Fig 4 (not shown). In another embodiment, Fig. 1 (not shown), the plate has a launching interdigital transducer (2) and a receiving transducer (3) forming a first delay line on one surface, and a similar delay line (4, 5) on the other surface, the two delay paths being of equal length D. The delay paths are connected in parallel in a regenerative feedback loop (6), Fig. 2 (not shown), of an amplifier (7). In other arrangements (not illustrated) the transducers and/or the delay paths may be connected in series. By making the lengths of the two delay paths slightly different the oscillator may be rendered tunable.