Patent GB-884325-A (GB)
Title: Improvements in non-linear resonant devices
IPC: H03K19/162
Filed: 1959-06-30
Abstract: 884,325. Parametrically-excited resonators. INTERNATIONAL BUSINESS MACHINES CORPORATION. June 30, 1959 [June 30, 1958], No. 22426/59. Class 40 (9). [Also in Group XIX] The inductance of a coaxial cable and the non-linear capacitance of biased semiconductor diodes which bridge the cable ends provide a resonant circuit having a voltage node for a frequency #1 midway between the diodes and voltage nodes for a higher frequency #2 at intermediate positions, an excitation voltage being applied to the cable at the #1 node position, while the intermediate #2 node positions provide input or output points for the #1 frequency. Usually the relationship #2 = 2#1 applies, and the cable has a minimum length of #/4, where # is the wavelength of frequency #1. As shown in Fig. 1, a coaxial cable 20 has semiconductor diodes 30, 32 positioned between conductive end plates 26, 28 and the inner conductor 24, and coaxial cables 40 and 50-58 are fitted into holes in the cable sheath 22, the cables 40, 50 and 52-58 being located at the #1 and #2 node positions respectively. Cable 40 provides a circuit over a dielectric rod 45 coated of resistive material for a voltage 38 which biases the diodes in their non-conductive sense, the rod being in direct contact with the inner conductors 24, 44 of cables 20 and 40. The remaining cables, on the other hand, have capacitive connections 64, 82-88 between their respective inner conductors and conductor 24. An excitation voltage source 96 of frequency #2 is connected to cable 50, this voltage and the bias voltage 38 being controlled by circuits 98, 100 for the purpose of initiating or terminating oscillation. It is stated that the bias voltage and circuit 100 may be dispensed with by using a self-biasing circuit comprising a higher resistance coating on rod 45 and a shortcircuit link between the inner and outer conductors of cable 40, in which case the device has the property of two stable oscillation amplitudes in addition to that of stable output phases. The device in Fig. 1 is shown schematically in Fig. 2, the cable 20 being represented by a line 104, the bias by a resistor 115, the #2 frequency input cable by 106 and the #1 frequency input and output cables by 108-114. Diodes 30, 32 terminate the cable ends. An application as an oscillator, Fig. 4 (not shown), is described in which the excitation frequency #2 at 106 is above a threshold value of amplitude, and a voltage of frequency #1 is impressed for a short duration on input 108, #2 being an integral multiple of #1. The device then establishes #1 outputs at 110 and 114, the two outputs being of respectively opposite phases. Alternatively, the excitation frequency #2 may be reduced below the threshold value of amplitude, in which case a continuous signal of frequency #1 at input 108 produces amplified outputs of respectively opposite phases at 110 and 114 by regenerative action. Instability develops at or near the threshold value. An alternative oscillator is described, Fig. 3 (not shown), in which one diode is replaced by a linear capacitance. A modification of Fig. 4 is also described in which a circulator, for example of the ferrite type, prevents the flow of output power to the input, Fig. 5 (not shown). An arrangement of two lines is shown in Fig. 6, one line being resonant to frequeney #1, the other being resonant to a frequency #3. Both lines are excited from a common #2 source 131 and the relationship #3=#2 - #1 applies. As shown, line 104 provides an output frequency #1 at 112 and output components of frequency #3 in couplings 132, 134, the latter frequency causing line 124 to resonate and provide output frequency #3 at 136 and 137. In this arrangement which may operate as an oscillator or amplifier, output power from line 124 passes back through line 104 to the #1 frequency input circuit 108. This defect is avoided in the amplifier circuit in Fig. 7 in which an input signal of frequency #1 is applied to terminal 1 of a circulator 116, and an output of the same frequency is obtained from terminal 3, the circulator having its terminal 4 connected to a reflectionless termination 122. An arrangement of lines to form a shift register or ring counter is also described in which each binary digit is represented by one or the other of two stable phases of frequency #1 input signals. As shown in Fig. 8, the input signals are applied in turn to coupling 218 of line 200, and are passed in succession through lines 202-204-206 to line 208 where they either appear as outputs at 220 or 261, or are recirculated through a switch 250. The output and input couplings of each pair of lines are linked by a unidirectional coupling 222-230 such as a diode, Fig. 9 (not shown). Stepping of the digits stored in the form of oscillations of one phase or the other from line to line is controlled by the excitation frequency #2 which causes an oscillation to terminate if the excitation voltage falls below a threshold value. Three separate sources E1, E2, E3 of excitation frequency are used, each source in turn reducing its output to a value below the threshold for a short time period so as to provide the output voltage pattern shown in Fig. 10. Two sources may alternatively be used, Fig. 11 (not shown), or the periods during which each source produces voltage above and below the threshold value may be equal, Fig. 12 (not shown).