Patent GB-975951-A (GB)
Title: Diode oscillators
IPC: H03B7/14
Filed: 1961-01-04
Abstract: 975,951. Semi-conductor oscillators. WESTERN ELECTRIC CO. Inc. Jan. 4, 1961 [Jan. 8, 1960], No. 363/61. Heading H3T. [Also in Division H1] In an oscillator circuit comprising two negative-resistance diodes which are biased on to negative-resistance portions of their characteristics by means of a biasing source connected in shunt therewith, the diodes being simularly poled with respect to the terminals of the source, and a frequency-determining reactive circuit connected between the diodes, resistive mode-suppression means is so connected into the circuit as to suppress oscillations of the diodes in undesired modes, e.g. in unison, and to permit oscillations in the desired mode, e.g. in push-pull only. In the circuit of Fig. I, voltage-controlled negative resistance diodes 1-1, 1-2 are biased on to negativeresistance portions of their characteristics by means of source V. The diodes are interconnected by two inductors of value L 1 , each shown as the series conbination of two separate inductors; these form a frequency-determining circuit together with the diode capacitances. A load of magnitude 2r is coupled to the circuit as shown. The circuit desirably oscillates in the push-pull mode with currents Ip flowing in series through the two diodes; the alternative unison mode in which currents Iu from the two diodes flow through the branch containing the source is suppressed by the inclusion of a resistor r 2  in that branch. The small inductance associated with the mode-suppression resistor is indicated by the inductor L 2 . A mathematical analysis is given showing the relationships which should exist between the circuit components for push-pull oscillations to be sustained and unison-mode oscillations to be suppressed. Fig. 4A shows a coaxial line oscillator corresponding to the circuit of Fig. 1. Diodes 1-1, 1-2 are arranged as shown at each end of inner conductor 11 and short-circuiting end-pieces to the line. The mode-suppression resistor 13 extends from the inner conductor through an aperture in the outer conductor from which it is separated by a dielectric sheath so as to provide a by-pass capacitor across the power supply 15; energy is extracted from the cavity through an aperture 16. Fig. 5 shows a circuit constituted by two diodes mounted on pedestals 22-1, 22-2 and connected between two conducting plates constituting the conductors of a strip transmission line. The mode-suppression means is constituted by two resistive slabs 24-1, 24-2 connected between the upper and lower conductors of the line. Fig. 6A shows a modified form of the circuit of Fig. 5 in which diodes 1-1, 1-2 having junctions small enough to be considered as spots are replaced by diodes in which the junctions 31-1, 31-2 extend over a line. The diodes are fabricated by alloying a semi-conductor slab 33 in contact with the upper conductor of the line to two ridges (thus forming the linear junctions) which rise from the lower conductor of the line and enclose a frequency-determining cavity 35. Resistive slabs 34-1, 34-2 are provided between the conductors for suppressing the unison-mode oscillations. In addition, standing waves, either in unison or in push-pull, may appear along the lengths of the junctions 31-1, 31-2. These are suppressed by the provision of a very close spacing d between the conductors over the central portion of the structure and by the provision of channels 36-1, 36-2 to either side of the diodes. Fig. 8 shows the oscillator of Fig, 6A coupled to a waveguide 41. A post 46 is introduced to control the coupling and to allow matching of the oscillator to its load. Specification 974,493 is referred to.